Surgical Infections Flashcards

Question

A 78-year-old man with a history of urinary retention and a chronic indwelling urinary catheter is admitted to the hospital from his nursing home with a new-onset altered mental status, and a catheter-associated urinary tract infection (CAUTI) is suspected. Which of the following is true regarding CAUTIs? A. A 7-day antibiotic treatment is adequate for patients whose symptoms respond promptly to treatment. B. A CAUTI can be sufficiently diagnosed by the presence of greater than 105 cfu/mL of at least one bacterial species in a urine specimen. C. Urine specimens being sent for culture can be obtained from the catheter bag. D. Pyuria is a specific indicator for urinary tract infections (UTIs). E. Proteus mirabilis is the most common organism cultured in CAUTIs.

Answer 1

A COMMENTS: CAUTIs are the most common health care–associ- ated infection worldwide, and the most important factor leading to nosocomial UTIs is urinary catheterization. The best prevention for CAUTIs is avoiding catheterization. There are a limited number of circumstances in which catheterization is appropriate, such as when monitoring urine output in critically ill patients, in patients with acute urinary retention or obstruction, in certain surgical procedures, or to facilitate healing of wounds or pressure ulcers in some patients with urinary incontinence. A CAUTI is diagnosed by the presence of greater than 103 cfu/mL of at least one bacterial species in a catheter urine specimen or a midstream-voided urine specimen in addition to clinical signs and symptoms suggestive of infection. Signs and symptoms of a UTI include new-onset fever, rigors, altered mental status, lethargy, malaise, flank pain, costovertebral angle tenderness, hematuria, suprapubic or pelvic discomfort, dysuria, urinary frequency, and urinary urgency. For these symptoms to be attributed to a catheter, the patient must have a current indwelling urinary catheter or have had one within the 48 h preceding his or her symptoms. Without these symptoms, an infection cannot be diagnosed. Catheter-associated asymptomatic bacteriuria is more likely, and this is diagnosed by the presence of greater than 105 cfu/mL of at least one bacterial species in a urine specimen. Catheters predispose to bacteriuria and UTIs in a variety of ways, but formation of a biofilm along the catheter itself is the most important predisposing factor. Pyuria is not specific for UTIs; it can be seen in a variety of other renal pathologies and should not be used as a diagnostic criterion for UTI. Urine culture specimens are best collected by removing the catheter, if possible, to obtain a voided midstream specimen, from the tubing or catheter itself in a catheter that has been in place for less than 2 weeks, or by removing any catheter that has been in place for greater than 2 weeks and obtaining a specimen from the new catheter. The duration of antibiotic therapy should be 7 days for patients whose symptoms respond promptly to antibiotics and 10 to 14 days for those whose symptoms respond slowly. Escherichia coli is the most common causative organism in CAUTIs, although Proteus is commonly cultured in patients with chronic indwelling catheters.

Answer 2

ANSWER: B COMMENTS: Answer A is acute hepatitis B infection; chronic infection requires HBsAg positivity for at least 6 months. A patient with chronic active infection (answer B) exhibits normal to mildly elevated liver enzymes and HBsAg positivity but negative HBsAb since the infection has not been cleared; HBcAb will be positive with chronic infection, and HBeAg may be positive as well if there is a continued high level of viral replication; this is usually accompanied by a high level of HBV DNA. This is different from an inactive carrier state (answer C); these patients have persistent HBV infection of the liver without significant hepatic necrosis or inflammation, so their liver enzymes are not significantly elevated; there is a low level of viral replication, which correlates with negative HBeAg. Patients who have cleared HBV infection have evidence of HBsAb and HBcAb positivity (answer D). Answer E reflects successful vaccination, with only HBsAb positivity on serologic testing.

Answer 3

A-b, B-e, C-d, D-a, E-c COMMENTS: Vancomycin is known to cause red man syndrome, a syndrome composed of flushing of the face, neck, and chest. It is better described as a hypersensitivity reaction, rather than a true allergy, because the effect is partly mediated by the speed with which it is transfused. Aminoglycosides can cause ototoxicity (cochlear and vestibular), which is dose dependent. The effects may begin to be seen even after cessation of the drug; aminoglycoside ototoxicity may be irreversible. INH can cause severe, sometimes fulminant, hepatitis that is largely indistinguishable from acute viral hepatitis. The mechanism of toxicity is not clear, but is thought to be related to direct toxicity of the drug or its metabolites, and is more likely to occur when other hepatitis risk factors are present, such as concurrent alcohol consumption, use of other drugs that utilize the cytochrome P450 system for metabolism, previous INH intolerance, or prior or concurrent liver disease. Fluoroquinolone- induced tendinopathy is rare, but it has been documented with almost all drugs in this class. Tetracyclines cause cutaneous photo- toxicity, so patients taking tetracyclines are cautioned to avoid sun exposure.

Answer 4

ANSWER: D COMMENTS: The SCIP summarizes specific tactics aimed at prevention of surgical site infections (SSIs). Of the answer choices listed above, only D is inaccurate; optimal blood glucose within the first 48 h of surgery is less than 200 mg/dL. Hyperglycemia impairs the host immune function and is known to increase the risk of infection in both diabetic and nondiabetic patients. Moderate hyperglycemia (i.e., blood glucose > 200 mg/dL) in the first 24 h following surgery increases the risk of SSIs by a factor of four. Tight blood glucose control has been a matter of debate in recent years, with some arguing that very strict blood glucose control (i.e., less than 110 mg/dL) results in significantly decreased rates of infection. However, postoperative hypoglycemia is associated with increased mortality, so glycemic goals have been relaxed. The remaining answer choices are correct. Prophylactic antibiotics should be given within 1h of incision, though 2h is appropriate for fluoroquinolones and vancomycin, due to the prolonged infusion times for these drugs. They should be discontinued within 24 h of the end of surgery in all cases aside from the cardiac surgery, where 48 h of prophylactic antibiotic therapy is appropriate. Razors should never be used to remove hair prior to procedures due to the increased risk for small breaks in the skin, which might introduce infection; clippers should be used preoperatively. Normothermia, defined as any temperature between 96.8°F and 100.4°F, should be maintained intraoperatively and for at least the first hour following surgery.

Answer 5

A-c, B-d, C-e, D-a, E-b COMMENTS: Prophylactic antibiotics administered preoperatively should be targeted to the organisms most likely to be encountered in the operative field. Broad-spectrum antibiotics do not have greater efficacy at preventing SSIs than more narrow-spectrum, targeted choices. The choice of prophylactic antibiotic therapy for intraabdominal surgeries varies widely depending on the exact location within the gastrointestinal tract that is being manipulated. Low-risk biliary tract procedures (e.g., elective laparoscopic cholecystectomy) do not require surgical site infection prophylaxis; however, patients undergoing open or complicated procedures involving the biliary tract should receive antibiotics covering enteric GNRs, Enterococcus, and Clostridia. Comparatively, colorectal surgery requires broad coverage of enteric GNRs, anaerobes, and Enterococcus, which may be accomplished with ertapenem, a carbapenem antibiotic. Cystoscopy with manipulation, such as the placement of ureteral stents, necessitates coverage of enteric GNRs and Enterococcus; compared with colorectal surgery, anaerobic coverage is not necessary. Vascular SSIs are most commonly caused by skin flora, such as Staphylococcus and Streptococcus species, so a first-generation cephalosporin, such as cefazolin, is adequate. In clean-contaminated head and neck cases (i.e., any surgical procedure involving the oropharyngeal mucosa), prophylactic antibiotics should cover both aerobic and anaerobic oral flora (such as Streptococcus, Bacteroides, and Peptostreptococcus).

Answer 6

ANSWER: B Recurrent C. difficile colitis is a growing health problem in the United States. Treatment of an initial episode can be accomplished with oral or IV metronidazole (500 mg every 8 h for 10 to 14 days) or oral vancomycin (125 mg every 6 h for 10 to 14 days). IV vancomycin is never acceptable as a treatment for C. difficile colitis. More severe initial infections should be treated with vancomycin rather than metronidazole. For a patient’s first relapse, if there is no evidence of systemic toxicity, treatment with the initial antibiotic regimen may be appropriate. Second relapses and beyond, however, require oral vancomycin in a tapered and pulsed fashion (see the following chart). Alternatively, fidaxomicin, a macrolytic antibiotic that is bactericidal against C. difficile, can be used. With both drugs, probiotics may be added, though their efficacy is still unclear. Fecal microbiota transplant has also been shown to be a cost-effective solution for recurrent C. difficile colitis. For patients developing evidence of systemic toxicity from C. difficile colitis, more aggressive therapy is required. Depending on the patient’s clinical stability, multiple avenues of treatment are available. Scheduled oral vancomycin or fidaxomicin can be given, with or without IV metronidazole; IV metronidazole may have enhanced efficacy in patients with evidence of bowel dysmotility. The duration of antibiotics in severe C. difficile colitis is generally at least 17 to 24 days (1 week beyond standard treatment). Intra- colonic vancomycin administration (i.e., vancomycin enema) is also an acceptable treatment method; metronidazole enema is not an accepted treatment, which makes answer E incorrect. Vancomycin enemas are particularly useful in patients who have conditions preventing oral vancomycin from reaching the colon (i.e., end ileostomies, severe ileus, colonic dysmotility, etc.). Patients who are severely ill with toxic megacolon, perforation, uncontrolled sepsis, or multiorgan failure should be considered operative candi- dates. The two most accepted surgical procedures are subtotal colectomy and diverting loop ileostomy with colonic lavage followed by antegrade vancomycin enemas. The pathogenesis of C. difficile infection rests largely on the disruption of normal colonic flora by other antibiotics. Those with inherent activity against C. difficile (i.e., those who have a robust antibody response to toxin A) are less likely to become clinically infected. One study reported that patients who did not develop antibodies to toxin A during their initial infection were 48 times as likely to develop a recurrent infection. Advanced age (>65 years) is predictive of both initial and recurrent infection. Additional patient-specific risk factors for infection include gastric acid suppression (either via PPIs or H2 blockers), recent gastrointestinal surgery, chemotherapy, stem cell transplant, and obesity. The three classes of antibiotics cited most frequently as causative agents are clindamycin, cephalosporins, and fluoroquinolones, and these agents are generally administered weeks to several months prior to the development of C. difficile infection. Concomitant use of multiple antibiotics and prolonged courses of antibiotics have also been found to be risk factors for infection; however, not all patients who are exposed to C. difficile and receive antibiotics develop an infection. Infection control policies are paramount to controlling the nosocomial spread of C. difficile infection; patients with active infections should be placed on contact precautions, and all healthcare workers (HCWs) who encounter the patient should wash their hands with soap and water since C. difficile spores are resistant to alcohol-based hand sanitizers. ``` Tapered and Pulsed Vancomycin Dosing for Recurrent C. difficile Infection: Tapered dosing: 125 mg four times daily for 10 to 14 days, followed by 125 mg twice daily for 7 days, and then 125 mg daily for 7 days Pulse dosing (after completion of the taper): 125 mg every 2 to 3 days for 2 to 8 weeks ```

Answer 7

ANSWER: C COMMENTS: Fever is a common postsurgical finding, but not all fevers require evaluation. In the first 72 h after surgery, fever is more likely related to postoperative inflammatory responses in the host, rather than infection, when the patient is otherwise asymptomatic or without an indwelling urinary catheter. While fever is expected in postoperative patients with evidence of diffuse infection preoperatively (such as large abscesses, purulent or feculent peritonitis, or necrotizing soft tissue infection), fevers that are persistent for greater than 96 h after appropriate surgical management, or recurrent fevers after 96 h, are concerning for recurrent or incompletely cleared infection. Fevers presenting greater than 96 h post-operatively are more likely to be due to infection. Surgical wounds should only be cultured if there are signs or symptoms suggestive of wound infection (i.e., purulence, tenderness, and erythema). SSIs are most commonly due to the native flora of the organ that was operated upon, but within the first 24 to 48 h of surgery, wound infections are more likely to be due to group A Streptococcus (GAS) or Clostridia, which are significantly more virulent organisms. Deep venous thrombosis, pulmonary embolism, and superficial thrombophlebitis are other possible etiologies that should be considered in the evaluation of a febrile postoperative patient.

Answer 8

ANSWER: D COMMENTS: Sinusitis is an infrequent but potentially life-threatening cause of fever in critically ill patients. When the ostia of the sinuses become obstructed (e.g., from nasotracheal intubation, nasogastric tube placement, or maxillofacial trauma), bacterial overgrowth can occur, and when drainage is impaired, infection results; approximately one-third of patients who are nasotracheally intubated develop sinusitis within 1 week. The diagnosis is suggested by clinical findings, including cough, purulent nasal dis- charge, tooth pain, fever, wheezing, or throat or tooth pain. Normal nasopharyngeal organisms are the most common causes, and infec- tions are often polymicrobial. GNRs are present in approximately two-third of cases of acute sinusitis in critically ill patients; gram- positive rods are isolated in approximately one-third of cases, and fungi are found in 5%–10%. A CT scan of the sinuses is the most sensitive imaging modality for diagnosing sinusitis, although plain films can be obtained as well. Plain films are less sensitive than CT scan, but the accuracy of plain films in diagnosis can be augmented if combined with the findings of nasal endoscopy, when performed by a skilled endoscopist. Needle aspiration of the sinuses to obtain fluid for cultures provides a definitive diagnosis, but a biopsy may be required to rule out invasive fungal sinusitis in immunocompromised patients.

Answer 9

ANSWER: C COMMENTS: Tetanus toxin, produced by C. tetani, an anaerobic gram-positive bacillus, causes disinhibition of lower motor neurons; it is taken up via lower motor neurons and transported proximally to the spinal cord and brainstem and then into inhibitory neurons, causing a functional denervation of motor neurons. This can result in lockjaw; muscle rigidity; and spasm of respiratory, laryngeal, and abdominal muscles, causing respiratory failure. Autonomic dysfunction can also be seen with tetanus, manifesting as labile blood pressure and heart rate. Tetanus- prone wounds include contaminated wounds (i.e., soil, saliva, and stool), crush wounds, or burn wounds. Treatment of tetanus- prone wounds includes local wound care (i.e., debridement and irrigation) and antibiotic therapy targeted against C. tetani. Depending on the completeness of a patient’s tetanus vaccination, additional therapy is required, based on the following tables: ``` TETANUS PRONE WOUNDS Previous Tetanus Toxoid Administration: 1) Less than three doses - Tetanus Toxoid - Tetanus Immunoglobulin ``` 2) Three or more doses - Tetanus Toxoid IF the last dose was prior to >5 years CLEAN WOUNDS Previous Tetanus Toxoid Administration: 1) Less than three doses - Tetanus Toxoid 2) Three or more doses - Tetanus Toxoid IF the last dose was prior to >10 years Tetanus immunoglobulin serves to bind tetanus toxin in the bloodstream to minimize absorption into motor neurons. Muscle spasm and rigidity should be treated if present.

Answer 10

ANSWER: C COMMENTS: PLAs are relatively uncommon and have vague presenting symptoms. The classic triad of fever, right upper quad- rant pain, and malaise is present in only about one-third of patients. PLAs have multiple causes including biliary tract disease causing obstruction, seeding from another intraabdominal infection via the portal vein, hepatic artery seeding or bacteremia, direct extension from an adjacent infection (such as cholecystitis and perinephric abscess), or trauma; a small percentage of cases are cryptogenic. Biliary tract disease is now the most common etiology of PLAs and includes cases of choledocholithiasis, biliary stricture, congenital anomalies of the biliary tree such as choledochal cysts, and obstructing tumors like cholangiocarcinoma or pancreatic adenocarcinoma. Most infections are polymicrobial, and E. coli is the most frequently isolated organism in the United States, followed by Kleb- siella pneumoniae. PLAs occur most frequently in the right lobe of the liver, given its greater portal venous flow. Treatment involves broad-spectrum antibiotics (though particularly targeted against enteric GNRs and anaerobes) with percutaneous drainage for patients who do not improve with 2 to 3 days of appropriate anti-microbial therapy, abscesses greater than 5 cm in diameter, or abscesses at risk of rupture. Surgical intervention is generally reserved for ruptured abscesses, failed response to percutaneous drainage, uncorrected primary pathology (e.g., biliary stricture), or multiloculated abscesses not amenable to percutaneous drainage.

Answer 11

ANSWER: A COMMENTS: Burn wound infections remain a major cause of morbidity and mortality in burn patients, especially in those with greater than 20% TBSA burns. Burn wounds have a greater propensity for infection than the healthy tissue since the wound lacks a barrier to environmental organisms, and devascularized burn tissue provides a protein-rich medium in which bacteria can thrive; in addition, burns cause significant systemic responses that inhibit a patient’s normal host defense and healing mechanisms. Most burns are colonized with bacteria early after injury but do not cause systemic symptoms. Topical antimicrobials help to reduce the rate of conversion into invasive wound infections; however, invasive infections do result in systemic symptoms and must be treated. Diagnosis of a burn wound infection requires positive histopathology: the burn must be biopsied, with the growth of >105 organisms per gram of burn wound tissue. Burn wound infections often mani- fest with physical changes in the appearance of the burn, such as conversion to a greater degree of burn and surrounding cellulitis. Because most burn patients exhibit the signs of a systemic inflammatory response syndrome (SIRS), the American Burn Association has developed criteria for specifically diagnosing burn wound sepsis: At least one of the following: • Culture-positive infection (i.e., blood, urine, wound) • Pathologic tissue source identified (>105 bacteria per gram of tissue on quantitative biopsy) • Clinical improvement with antimicrobial therapy At least three of the following: • Temperature greater than 102.2°F or less than 97.7°F • Progressive tachycardia • Progressive tachypnea • Thrombocytopenia that occurs greater than 3 days after initial resuscitation • Refractory hypotension • Leukocytosis > 12,000 or <4000 WBCs/cells MCL • Hyperglycemia • Inability to tolerate enteral feedings for >24 h

Answer 12

ANSWER: E COMMENTS: GAS, or group A S. pyogenes, is an aerobic gram-positive coccus that is responsible for a wide range of clini- cal illnesses, accounting for greater than 600 million infections globally each year. The infections caused by GAS vary in clinical severity, from mild cellulitis to life-threatening toxic shock syndrome, as demonstrated by the answer choices above. GAS is also responsible for a variety of postinfectious immune-mediated diseases, such as acute rheumatic fever or poststreptococcal glomerulonephritis. All the answer choices above can be classically attributed to GAS infection except for meningitis, which is more commonly caused by group B Streptococcus, particularly in newborns. GAS, which colonizes epithelial surfaces, is almost universally sensitive to penicillin. Its main virulence factor is the M protein, which is a surface antigen and virulence factor encoded by the emm gene, of which there are over 200 types. Different emm types are associated with different types of infection; some are known to cause cutaneous infection, while others cause invasive infection. The prevalence of different emm types is also socioeconomically distinct, with certain emm types being seen in more industrialized areas compared with other types being prevalent in more rural communities. Geography plays a role as well, with variability in the prevalence of emm types based on region.

Answer 13

ANSWER: C COMMENTS: Asplenic patients (those who have either undergone splenectomy or are functionally asplenic, such as in sickle cell disease) are at an increased risk for a fulminant and potentially rapidly fatal overwhelming bloodstream infection caused by encapsulated organisms. This is due to impaired bacterial clearance, especially of encapsulated organisms (i.e., S. pneumoniae, Neis- seria meningitidis, and H. influenzae), and impaired humoral (not cellular) immunity. The risk of developing postsplenectomy sepsis varies based on the indications for splenectomy, the age at which the patient underwent splenectomy (or became functionally asplenic), and the time interval since splenectomy (or functional asplenia). In terms of indication for splenectomy, patients who have undergone splenectomy for trauma are at the lowest risk; those who have undergone splenectomy for hereditary spherocytosis or immune thrombocytopenic purpura are at intermediate risk; and the greatest risk patients are those who are functionally asplenic due to α-thalassemia, sickle cell disease, or portal hypertension. Children (especially those under the age of 5 years) are at a greater risk for developing sepsis than are adults, but this may also be confounded by the indications for splenectomy or functional asplenia in this age group. Overall, the risk for postsplenectomy sepsis is greatest in the first year following splenectomy, but patients who have undergone splenectomy are at an increased risk for sepsis for approximately 10 years following surgery. Since the year 2000, when universal vaccination with the heptavalent pneumococcal conjugate vaccine (PCV7) in children began, the rates of invasive pneumococcal infection have dropped significantly, and the rates have continued to fall with the development of the 13-valent vaccine (PCV13) in 2010. Patients who undergo splenectomy or are functionally asplenic should receive vaccinations for the encapsulated organisms prior to splenectomy if it is elective or prior to discharge if performed urgently. Treatment of postsplenectomy sepsis should be rapid. A fever in any postsplenectomy patient should prompt initiation of antimicrobial therapy as it may be the only sign of an impending fulminant infection. Postsplenectomy patients, even those who have undergone vaccination for S. pneumoniae, N. meningitidis, and H. influenzae, should be counseled to seek medical attention with any febrile episode. The most common causative organism is S. pneumoniae, so ceftriaxone, which is also active against H. influenzae and N. meningitidis, is appropriate. Vancomycin should be administered as well due to concerns for penicillin-resistant pneumococcus and β-lactamase–producing H. influenzae. Antibiotics should be administered immediately and should not be delayed to obtain cultures.

Answer 14

ANSWER: A COMMENTS: Surgery for the treatment of peptic ulcers is indicated only in the following circumstances: intractable hemorrhage, perforation, and obstruction. The patient does not have any of these conditions. Furthermore, H. pylori infection, the most important pathophysiologic factor in the development of duodenal ulcer, was never adequately treated. Treatment options for H. pylori infection are numerous, but they must always include an H2 blocker or a PPI plus at least two antibiotics. The antibiotics most commonly used are amoxicillin, clarithromycin, and metronidazole. Bismuth-containing regimens have also been used. Depending on the combination used, the length of treatment varies from 2 to 4 weeks. Methods of detecting H. pylori can be divided into two categories: invasive and noninvasive. Biopsy and the CLO test require endoscopy, but all the other tests do not. Like the CLO test, the urea breath test takes advantage of the ability of H. pylori to split urea. However, the urea breath test only requires the patient to “blow,” whereas the CLO test is conducted on a piece of tissue. The serologic test for H. pylori antibody is useful but of limited value in determining the success of the therapy. There is no stool “antibody” test for H. pylori, but a stool antigen test is available and is as sensitive as the urea breath test. Since there is no need for repeated endoscopy in this patient, the clinician must consider the relative merits of the noninvasive methods. Because antibody test results may remain positive after treatment, the best choice is the urea breath test, which helps deter- mine the presence of live H. pylori.

Answer 15

ANSWER: E COMMENTS: Anaerobic bacteria are normal inhabitants of the skin, mucous membranes, and gastrointestinal tract. In fact, anaerobic bacteria outnumber aerobic organisms by more than 10:1 in the oral cavity and by more than 1000:1 in the colon. Therefore it is not surprising that anaerobes are cultured from up to 90% of intraabdominal abscesses. The most common pathogens in this group are Bacteroides spp. Bacteroides fragilis is an important copathogen in the pathogenesis of intraabdominal abscesses. As with most serious infections, proper treatment involves appropriate drainage of abscesses and debridement of devitalized tissue when present, as well as appropriate antibiotic therapy. Antibiotics with excellent broad-spectrum anaerobic activity include the carbapenems (imipenem, meropenem, and ertapenem), â-lactam/â-lactamase combinations (ampicillin/sulbactam, ticarcillin/ clavulanate, and piperacillin/tazobactam), and metronidazole. Although the second-generation cephalosporins (i.e., cefoxitin and cefotetan) and clindamycin also provide anaerobic coverage, over the past decade an increase in resistance of Bacteroides organisms to these agents has been observed. For example, as many as 30% of B. fragilis isolates are resistant to clindamycin.

Answer 16

ANSWER: A COMMENTS: Candidemia is associated with significant morbidity (e.g., endocarditis, septic arthritis, and ophthalmitis) and mortality (approximately 40%). Management of candidemia, particularly in patients with intravascular devices, remains controversial. Although the bloodstream in some patients—usually those who are immunocompetent—spontaneously clears after removal of the intravascular device, other patients—particularly those who are immunosuppressed—have disseminated disease and require systemic antifungal therapy. There are no accurate diagnostic tests or methods for selecting high-risk patients to determine those who require systemic antifungal therapy. Therefore all patients with at least one positive blood culture result for Candida should be treated with an antifungal agent. All nonsurgically implanted lines should be removed, and if continued central venous access is required, a new line should be placed at a new site (not exchanged over a guidewire). Some would attempt to sterilize the bloodstream without the removal of tunneled catheters or subcutaneous ports. However, in patients with persistent candidemia or septic shock, these devices should also be removed. Amphotericin B and fluconazole appear to have similar efficacy in the treatment of candidemia. Voriconazole and caspofungin are new antifungal agents that are also effective against Candida. These agents may be particularly useful for non-albicans species such as Candida krusei or Candida glabrata, which are less susceptible to fluconazole. All patients with candidemia should be evaluated for manifestations of disseminated disease, such as ocular involvement or OM. Candida identified from a surgical drain most likely represents colonization and does not require systemic antifungal therapy. Mucocutaneous candidiasis can be treated with local nystatin or clotrimazole.

Answer 17

ANSWER: D COMMENTS: The patient has acute epiglottitis, most likely attributable to H. influenzae type B, which is recovered from the blood in up to 100% of cases. Classically, the patient is a 2- to 4-year-old boy with a short history of fever, irritability, dysphonia, and dysphagia, which can occur at any time of the year. The widespread use of H. influenzae type B vaccine in developed countries has led to a marked decline in invasive disease with this organism. However, the disease is still common in developing countries. Haemophilus species are gram-negative coccobacilli. Treatment includes early intubation, with plans for a cricothyroidotomy or a tracheotomy if intubation fails, and an antibiotic such as ceftriaxone or ampicillin/sulbactam.

Answer 18

ANSWER: E COMMENTS: Several risk groups have been identified in whom HIV testing is indicated, including persons with sexually transmitted diseases and persons in high-risk categories, such as injected drug users, homosexual and bisexual men, hemophiliacs, patients with active tuberculosis (TB), and pregnant women. Donors of blood or organs should be tested. Certain clinical or laboratory findings should also prompt HIV testing. Such findings include idiopathic thrombocytopenia, oral hairy leukoplakia, reactivation varicella-zoster virus infection involving more than one dermatome, unexplained oral candidiasis, persistent vulvovaginal candidiasis, and herpes simplex virus infection resistant to treatment.

Answer 19

ANSWER: A COMMENTS: Hydatid cyst disease is caused by Echinococcus, with E. multilocularis and E. granulosus being the most common species causing infection in humans. The definitive hosts of these parasites are dogs, and the intermediate hosts are most commonly sheep or goats; humans are incidental hosts. Albendazole is the preferred antiparasitic therapy for Echino- coccus. Mebendazole is also an option, although it has less in vitro activity than albendazole. Benzimidazole agents interfere with parasite glucose absorption. The goals of drainage procedures, either surgical or percutane- ous, for hepatic echinococcal cysts are inactivation of the parasites and evacuation and obliteration of the cyst cavity; surgical proce- dures also include the removal of the germinal layer of the cyst cavity. Radical surgical procedures, such as pericystectomy, partial hepatectomy, or lobectomy, are preferred over less invasive surgical techniques. PAIR (puncture, aspiration of the cyst, injection of a scolicidal solution such as hypertonic saline, and reaspiration of cyst contents) is generally the preferred percutaneous drainage procedure. Any drainage procedure should be preceded by the use of a benzimidazole (i.e., albendazole or mebendazole) to sterilize the cyst contents and reduce the risk of anaphylaxis and echinococcal dissemination. Cystobiliary communication is likely relatively common in hepatic echinococcal disease, but the majority of cases are not clinically apparent. Magnetic resonance cholangiopancreatography has a sensitivity of 92% in diagnosing intrabiliary rupture, whereas CT scan has only 75% sensitivity. Endoscopic retrograde cholangiopancreatography (ERCP) is also very sensitive (86%–100%) and can be used for therapeutic intervention. ERCP with sphincterotomy effectively treats cholangitis related to cystobiliary com- munication, and some studies have shown that it can decrease the rate of postoperative biliary fistula formation.

Answer 20

ANSWER: C COMMENTS: Severe sepsis is characterized by multiorgan dysfunction with or without shock and is due to a generalized inflammatory and procoagulant response to infection. Efforts to improve the outcome with anticytokine therapy along with antibiotics and supportive care have until recently not been associated with improved survival. Recently, a randomized, double-blind, placebo-controlled multicenter trial evaluating recombinant activated protein C has demonstrated a survival benefit in patients with severe sepsis. However, activated protein C treatment was associated with an increased risk for bleeding and is contraindicated in patients with recent hemorrhagic stroke. Fluid resuscitation and antibiotics are mainstays in the treatment of sepsis. Intensive insulin therapy that maintains serum glucose levels at 80 to 110 mg/dL reduces morbidity and mortality in critically ill patients. The mechanism is unknown, but it is possible that correcting hyper- glycemia may improve neutrophil function. The use of corticosteroids for sepsis remains controversial. High doses of corticosteroids may in fact worsen outcomes by increasing the frequency of secondary infections. However, low doses of corticosteroids may be beneficial in septic patients who may have “relative” adrenal insufficiency despite elevated levels of circulating cortisol. Although the issue is controversial, the use of low-dose hydrocortisone is not contraindicated in this patient.

Answer 21

ANSWER: C COMMENTS: Antibiotic prophylaxis for endocarditis is recommended for patients with certain cardiac conditions who are undergoing any dental procedure that involves the gingival tissues or periapical region of a tooth and for any procedure involving perforation of the oral mucosa. In addition, patients undergoing procedures on the respiratory tract or those with skin or soft tissue infections should also receive prophylaxis. The cardiac conditions associated with the highest risk for adverse outcomes from infective endocarditis for which prophylaxis is indicated prior to the previously listed procedures include prosthetic heart valves, history of infective endocarditis, congenital heart disease (CHD) limited to unrepaired cyanotic CHD, repaired CHD with prosthetic material or devices during the first 6 months after the procedure, repaired CHD with residual defects at the site or adjacent to the site of a prosthesis, and cardiac transplantation recipients with cardiac valvulopathy. Prophylaxis against viridans group streptococci with a penicillin, cephalosporin, or clindamycin is recommended. Routine prophylaxis in patients undergoing gastrointestinal or genitourinary procedures is no longer recommended.

Answer 22

ANSWER: A COMMENTS: Up to 90% of HIV-infected patients with advanced disease (<100 CD4+ cells/mm3), multiple ring-enhancing lesions, and a positive Toxoplasma IgG antibody have cerebral toxoplasmosis. Empiric treatment with pyrimethamine, sulfadiazine, and folinic acid is recommended. Most patients with central nervous system (CNS) toxoplasmosis respond rapidly to this therapy, with nearly 90% of patients demonstrating neurologic improvement at 2 weeks. Radiographic improvement occurs at a slower pace, with approximately 50% improvement on repeated MRI of the brain occurring within 3 weeks of initiating treatment. For patients who do not improve by 2 weeks, a brain biopsy is indicated. Although lymphoma is the most likely alternative diagnosis in patients with acquired immunodeficiency syndrome (AIDS) and CNS lesions, up to 25% of brain biopsy specimens reveal toxoplasmosis. Thallium-201 (SPECT) or PET scans may provide useful information in that a “cold” lesion revealed by SPECT or hypometabolic lesions seen on PET scanning are consistent with infection. However, false-positive and false-negative results can occur with these functional imaging studies. The addition of corticosteroids may be useful in the treatment of increased intracranial pressure. However, this antiinflammatory effect may make interpretation of clinical and radiographic responses difficult.

Answer 23

ANSWER: A-a; B-c, d; C-a; D-b; E-b COMMENTS: All the antimicrobial agents listed above are bactericidal agents (i.e., their associated mechanisms of action result in bacterial death). Bacteriostatic agents (e.g., tetracyclines, chloramphenicol, erythromycin, clindamycin, and linezolid) act by prevent- ing bacterial growth but do not result in bacterial death. They work primarily through inhibition of ribosomal protein synthesis. Both carbapenems and cephalosporins are â-lactam antibiotics and hence have a similar mode of activity. Enzymes located within the bacterial cytoplasmic membrane are responsible for peptide cross-linkage. These enzymes are called penicillin-binding proteins (PBPs) and are the site at which â-lactam drugs bind. Such binding interferes with bacterial cell wall synthesis and eventually results in cell lysis. Gram- negative bacteria contain a variable number of various PBPs. Each â-lactam antibiotic has different affinities for the different PBPs. Vancomycin is a glycopeptide that also inhibits bacterial cell wall synthesis and assembly. Vancomycin complexes to cell wall precursors and prevents elongation and cross-linkage, thereby making the cell susceptible to lysis. This antibacterial activity is limited to gram- positive organisms. Aminoglycosides bind irreversibly to the 30S bacterial ribosome and interfere with protein synthesis. For this activity to take place, they must penetrate the cell wall, which occurs optimally under aerobic conditions. Unlike other antibiotics that inhibit protein synthesis, aminoglycosides are bactericidal. This feature is due to their disruptive effect on calcium and magnesium homeostasis within the cell wall. Quinolones inhibit topoisomerase II (DNA gyrase) and topoisomerase IV, which impairs DNA synthesis in bacteria. Appreciation of the mechanism of action of antimicrobials may have a bearing on the selection of alternative therapies when bacterial resistance to the drug of choice develops.

Answer 24

ANSWER: D COMMENTS: Diabetic patients have a higher risk for foot infections because of factors such as vascular insufficiency, decreased sensation, hyperglycemia, and impairment of the immune system, particularly neutrophil dysfunction. Deep tissue biopsy of the infected foot is the preferred method of culture. Acute diabetic foot infections are often caused by monomicrobial aerobic gram-positive cocci (S. aureus and â-hemolytic streptococci, especially group B), whereas patients with chronic wounds and those who have recently received antibiotic therapy generally have polymicrobial gram-positive and gram-negative aerobes and anaerobes within their wound, including enterococci, Enterobacter, obligate anaerobes, and P. aeruginosa. Initial therapy is usually empiric and based on the severity of infection and available microbiology data (culture results or Gram stain). A majority of mild infections can be treated with orally dosed antimicrobials directed against aerobic gram- positive cocci. In patients with more severe infections or extensive chronic infections, parenteral broad-spectrum antibiotics with activity against gram-positive cocci (including MRSA) and gram- negative and obligate anaerobic organisms are warranted. The diagnosis of infection in patients with chronic wounds includes the presence of purulent secretions (pus) and two or more of the following: redness, warmth, swelling or induration, and pain or tenderness. MRSA infections are associated with worse outcomes, and impaired host defenses allow low-virulence colonizers such as coagulase-negative staphylococci and Corynebacterium spp. to become pathogens. In addition to antibiotics, early incision and drainage of abscesses with debridement of devitalized tissue, immobilization, and supportive care are important in the total management of a diabetic foot. In the presence of significant vascular insufficiency, revascularization of the distal end of the lower extremity may improve healing and prevent amputation. Radioactive studies using technetium-99 (bone scan) or gallium citrate or indium-labeled leukocyte scans have poor specificity and should not be performed routinely. MRI has become the imaging study of choice for diagnosing OM. Continued use of antimicrobials is not warranted for the entire time that the wound is open or for the management of clinically uninfected ulceration either to enhance wound healing or as prophylaxis against infection. Local wound care with sharp debridement of necrotic or unhealthy tissue promotes wound healing and removes a potential reservoir of pathogens. Avoiding direct pressure on the wound and providing off-loading devices facilitate wound healing. Administration of granulocyte colony-stimulating factors does not accelerate the resolution of infection but may significantly reduce the need for operative procedures.

Answer 25

ANSWER: A-e; B-a, d, e; C-a; D-b; E-c COMMENTS: Amphotericin B remains an important agent for the treatment of systemic mycotic infections, including candidiasis, mucormycosis, cryptococcosis, histoplasmosis, coccidioidomycosis, sporotrichosis, and aspergillosis. Amphotericin B is a fungi- cidal agent. Binding of amphotericin B to ergosterol in the fungal cell membrane alters permeability, with leakage of intracellular ions and macromolecules, leading to cell death. Adverse events such as infusion reactions and nephrotoxicity are common with the conventional (deoxycholate) form of the drug. New lipid formulations of amphotericin B have been developed and are associated with a reduction in toxicity without sacrificing efficacy. Newer triazoles (voriconazole and posaconazole) and echinocandins (caspofungin, micafungin, and anidulafungin) are emerging as alternative broad-spectrum antifungal agents. Histoplasmosis is predominantly a pulmonary infection caused by Histoplasma capsulatum, a dimorphic fungus endemic to the Mississippi and Ohio River valleys and along the Appalachian Mountains. Histoplasmosis has been associated with massive enlargement of the mediasti- nal lymph nodes secondary to granulomatous inflammation. During the healing process, fibrotic tissue can cause postobstructive pneumonia or constriction of the esophagus or superior vena cava and result in dysphagia or superior vena cava syndrome (or both). Actinomycosis is caused by a group of gram-positive higher-order bacteria that are part of the normal flora found in the oral cavity, gastrointestinal tract, and female genital tract. Typically, infections with Actinomyces spp. often occur after disruption of mucosal surfaces and lead to oral and cervical disease, pneumonia with empyema, and intraabdominal or pelvic abscesses. Placement of intrauterine devices has been associated with pelvic abscess secondary to this organism. Sinus tract formation is common as these organisms extend, unrestricted, through tissue planes. High-dose penicillin and surgical drainage are generally required for cure. Nocardia spp., other higher-order bacteria, are found in soil, organic matter, and water. Human infection occurs after inhalation or skin inoculation. Chronic pneumonia can occur, usually in immunocompromised patients. Skin lesions and brain abscesses are common with a disseminated infection. Prolonged treatment with sulfonamides in combination with other antibiotics is required for cure. C. neoformans causes meningitis and pulmonary disease. Infection is common in the setting of immunodeficiency, such as organ transplantation and AIDS, but it may also occur in immunocompetent hosts. C. albicans is a common inhabitant of the mucous membranes and gastrointestinal tract. Intertrigo is one form of cutaneous candidiasis that occurs in skinfolds where a warm moist environment exists. Vesiculopustules develop, enlarge, rupture, and cause maceration and fissuring. Obese and diabetic patients are at risk for the development of candidal intertrigo. Local care, including nystatin powder, is usually effective.

Answer 26

ANSWER: E COMMENTS: SBP is a monomicrobial infection, with enteric GNRs accounting for 60%–70% of the episodes of SBP. E. coli is the most frequently recovered pathogen, followed by K. pneumoniae. Streptococcal species, including pneumococci and enterococci, are also important pathogens. Ascitic fluid culture results are negative in many cases, but inoculation of blood culture bottles at the bedside yields bacterial growth in approximately 80% of cases. SBP most likely develops from the combination of prolonged bacteremia secondary to abnormal host defense, intrahepatic shunting, and impaired bactericidal activity of ascetic fluid. Transmural migration of gut flora and trans-fallopian spread of vaginal bacteria to the peritoneal space may also occur. Initial antimicrobial treatment should include coverage against aerobic gram-negative organisms. A third-generation cephalosporin, such as cefotaxime or ceftriaxone, is a reasonable choice. The duration of antibiotic treatment is unclear; 2 weeks has been suggested, but shorter courses (5 days) may have similar efficacy. Although the in-hospital mortality rate approaches 40%, infection-related mortality has declined sig- nificantly (10%). Unfortunately, the probability of recurrence is 70% at 1 year, with 1- and 2-year survival rates being 30% and 20%, respectively.

Answer 27

ANSWER: C COMMENTS: Randomized trials have demonstrated that secondary prophylaxis with oral norfloxacin, 400 mg/day, or trimethoprim/ sulfa- methoxazole, one double-strength tablet five times per week decreases the risk for recurrent SBP from 68% to 20%. However, overall mortality in these patients remains unchanged compared with those not receiving secondary prophylaxis. Another observation is that long- term quinolone use has been associated with the development of infection with quinolone-resistant bacteria. In approximately 30%–40% of patients with cirrhosis hospitalized for acute gastrointestinal bleeding, infection develops during the hospitalization. Norfloxacin (400 mg a day for 7 days) decreases the incidence of infective episodes involving gram-negative bacteria. The risk for SBP increases tenfold in patients with an ascitic fluid protein concentration of less than 1 g/100 mL fluid. Norfloxacin, 400mg/day, during hospitalization decreases the incidence of SBP in these patients as well. Patients hospitalized while awaiting liver transplantation are probably at risk for SBP and may therefore benefit from antibiotic prophylaxis. Active infection is a contraindication to liver transplantation.

Answer 28

ANSWER: B COMMENTS: Secondary peritonitis usually occurs because of perforation of an intraabdominal viscus such as perforated peptic ulcer, appendix, or diverticulum or penetrating gastrointestinal trauma. The infection is polymicrobial, with facultative aerobes and anaerobes acting synergistically. One study revealed an average of 2.5 anaerobes and 2 facultative aerobes identified per case of secondary peritonitis. E. coli is the most common isolate in culture. Bacteroides spp. are the most frequent anaerobes cultured from abdominal infections. About 1012 bacteria reside in the colon per gram of feces, with 90% of these bacteria being anaerobic organisms. Any process that impairs immunologic function or is associated with general debilitation increases mortality. Age, cancer, hepatic cirrhosis, and the presence of a systemic illness have been shown to increase mortality. One of the defense mechanisms of the peritoneal cavity is the production of fibrin to sequester bacteria for limiting systemic spread. Such sequestration leads to the formation of intraabdominal abscesses, which generally require drainage for cure. Treatment of secondary peritonitis requires surgical intervention for removal of the source of infection and systemic antibiotics for eradication of residual bacteria. Antibiotics selected should include agents with broad-spectrum coverage for fac- ultative aerobes, gram-negative bacilli, and anaerobes. Carbapenems are a good empiric choice for treatment. Aminoglycosides and fourth- generation cephalosporins lack anaerobic activity.

Answer 29

ANSWER: D COMMENTS: CMV is the most important pathogen affecting recipients of solid organ transplants. Symptomatic CMV disease may develop in as many as 50% of allograft recipients, usually 2 to 6 months after transplantation. CMV-seronegative recipients who are primarily infected are at the greatest risk for the development of severe CMV disease. Primary infection can occur through the donor organ, unscreened blood products, or intimate contact with a viral shedder. Reactivation of latent infection is less likely to cause severe disease. Patients receiving muromonab-CD3 (OKT3)/antilymphocyte globulin (ALG) therapy for acute rejection also appear to be at risk for the development of CMV disease. In addition to clinical disease directly attributable to CMV infection, CMV has indirect immunomodulatory activity. Symptomatic CMV infections are associated with an increased incidence of bacterial infections and opportunistic infections such as aspergillosis and Pneumocystis carinii pneumonia. In heart transplant patients, acute rejection and accelerated atherosclerosis are associated with CMV infection. Ganciclovir is the most commonly used agent for the prevention of CMV infection and disease; however, there is growing concern regarding the emergence of ganciclovir resistance.

Answer 30

ANSWER: C COMMENTS: The patient probably sustained a basilar skull fracture and a dural rent, with subsequent development of a dural fistula from the subarachnoid space and nasal cavity or paranasal sinuses. Cerebrospinal fluid rhinorrhea may occur and can easily be diagnosed by detecting the presence of â2-transferrin in nasal secretions. In patients with known basilar skull fracture, cerebrospinal fluid rhinorrhea develops in approximately 10% of the cases. Of these patients, bacterial meningitis develops in up to 30%. S. pneumoniae is the most common pathogen (65% of cases). Other organisms, such as H. influenzae, N. meningitidis, and S. aureus, account for the remaining cases. Empiric treatment should include an extended-spectrum cephalosporin (ceftriaxone, cefotaxime, or cefepime) and vancomycin since the incidence of â-lactam–resistant pneumococci is increasing. Prophylactic antibiotics have no proven benefit and may predispose to meningitis from antibiotic- resistant gram-negative bacteria. A recent prospective study demonstrated a survival advantage in patients with pneumococcal meningitis who received corticosteroids before or at the time of antibiotic administration. Spontaneous closure of the dural fistula is less likely in patients with a delayed manifestation of cerebrospinal fluid leakage with meningitis, and surgical repair is indicated. Diagnostic studies to identify the site of the fistula and treatment of any CNS infection should be completed before surgical intervention.

Answer 31

ANSWER: D COMMENTS: Persons with acute HCV infection are typically asymptomatic (60%–70%) or have a mild clinical illness. Fulminant hepatitis is rare. Chronic HCV infection develops in approximately 75%–80% of persons with acute HCV infection. Cirrhosis develops in 10%–20% of chronically infected individuals, usually after more than 20 years of infection. Liver failure from chronic HCV infection has become the leading indication for liver transplantation. Increased alcohol use, male gender, HIV coinfection, and HCV genotype 1 are associated with more severe liver disease. Hepatocellular carcinoma can be a late complication in 1%–2% of patients with cirrhosis. Antiviral therapy is recommended for individuals at an increased risk for progressive liver disease, as demonstrated by persistently elevated serum transaminase levels, detectable HCV RNA levels, and moderate inflammation in liver biopsy specimens. The prevalence of HCV infection is highest in injected drug users and patients undergoing hemodialysis. Overall, nearly 2% of the U.S. population has persistent HCV infection. Although trans- mission of HCV to HCWs occurs after approximately 3% of needlestick exposures involving HCV-infected patients, the prevalence of HCV infection in HCWs, including surgeons, is like the general population.

Answer 32

ANSWER: B COMMENTS: Recent Centers for Disease Control and Prevention (CDC) guidelines recommend that all patients with active pulmonary TB receive four-drug therapy consisting of INH, RIF, pyrazinamide, and ethambutol for the initial 2 months of treatment. For patients with drug-susceptible TB and negative sputum test results after 2 months of therapy, treatment can be completed with 4 months of INH and RIF. Extrapulmonary disease requires 6 to 9 months of treatment, except for meningitis, which is treated for 1 year. HIV-infected individuals are treated similar to non–HIV-infected patients with TB. However, significant drug–drug interactions may occur with antiretroviral agents and TB drugs and may alter therapeutic decisions. Treatment failures are generally due to nonadherence by patients to multidrug regimens. Currently, local health departments have directly observed therapy programs to improve compliance with and completion of anti-TB medication regimens. Another cause of treatment failure is infection with multidrug-resistant strains of M. tuberculosis. Conditions associated with a higher rate of resistance include TB in those known to have a higher prevalence of drug resistance, such as Asians or Hispanics and previously treated individuals; the persistence of culture-positive sputum after 2 months of therapy; and known exposure to drug-resistant TB. Certain individuals are at considerable risk for the development of active TB once infected (latent TB). TB skin testing (Mantoux/ PPD) is useful for identifying latent TB in high-risk individuals. Three cut points have been recommended for defining a positive tuberculin reaction: greater than 5 mm, greater than 10 mm, and greater than 15 mm of induration. Persons considered at highest risk (>5 mm of induration) include individuals with HIV infection, recent contacts with TB patients, and organ transplant patients. Individuals also at risk (>10-mm induration) include injectable drug users, residents of nursing homes and prisons, hospital employees, and recent immigrants from countries with a high prevalence of TB. These individuals, who are at a considerable risk for the development of active TB once infected, should receive 9 months of INH therapy.

Answer 33

ANSWER: E COMMENTS: Vascular graft infections can manifest in a variety of ways, and surgeons must maintain a high index of suspicion for graft infection. There are multiple mechanisms by which vascular grafts can become infected: perioperative contamination (including from lymphatic disruption), seeding from bacteremia, contiguous spread from an adjacent infectious process, and erosion of the graft into the gastrointestinal or genitourinary tracts. Grafts are more prone to infection than natural tissue since bacteria adhere to graft material and form a biofilm that resists the body’s natural immunologic defenses. The most likely organisms in vascular graft infections are gram-positive cocci such as S. aureus (the most common pathogen) and S. epidermidis, but the incidence of GNR infections is significantly increased in abdominal aortic, aortofemoral, and infrainguinal vascular graft infections. Gram-negative infections are more virulent than gram-positive infections, because gram-negative organisms produce proteases, elastases, and other destructive enzymes, which can cause anastomotic disruption and vessel rupture. In the vast majority of cases of vascular graft infection, the prosthetic material must be excised for complete eradication of the infection.

Answer 34

ANSWER: E COMMENTS: OM impairs healing of the wound and acts as a nidus for recurrent infection. It should be suspected in any deep or extensive ulcer, in one that overlies a bony prominence, and in an ulcer that does not heal after 6 weeks of appropriate therapy. In addition, concern for OM is raised in a patient with a swollen foot and a history of foot ulceration, the presence of a “sausage toe” (red, swollen digit), unexplained high WBC count, or inflammatory markers. Bone destruction underneath an ulcer seen on radiographs or probing of an ulcer down to bone is OM until proved otherwise. MRI is the most useful available imaging modality to diagnose OM, as well as to characterize any underlying soft tissue infection. The “gold standard” for diagnosis of OM remains isolation of bacteria from a bone sample with concomitant histologic findings of inflammatory cells and osteonecrosis. When treating a diabetic foot infection, if there are no hard signs to indicate the presence of OM and plain radiographs do not demonstrate any evidence of bone pathology, the patient should be treated for about 2 weeks for the soft tissue infection. If there is a persistent concern for OM, plain films should be repeated in 2 to 4 weeks to look for evidence of cortical erosion, periosteal reaction, or mixed radiolucency and sclerosis. Radioisotope scans are more sensitive than plain radiographs for diagnosis but are expensive and can be time consuming. If findings on plain films are only consistent with but not characteristic of OM, the clinician should consider the following: (1) additional imaging studies—MRI is preferred but nuclear medicine scans with leukocyte or immunoglobulin techniques would be the second choice; (2) empiric treatment for an additional 2 to 4 weeks with repeated radiographs to look for progression of bone changes; and (3) bone biopsy (operative or percutaneous fluoroscopic or CT guidance), especially if the etiologic pathogen or susceptibilities need to be established. Some physicians would perform biopsies for midfoot or hindfoot lesions because these are more difficult to treat and lead to higher-level amputations. Traditionally, resection of a bone with chronic OM was necessary for cure; however, some nonrandomized case series report clinical success in 65%–80% of patients treated nonoperatively with prolonged (3 to 6 months) antibiotic therapy. When treatment of OM fails, the clinician should consider whether the original diagnosis was correct; whether there is any remaining necrotic or infected bone or surgical hardware that needs to be removed; and whether the antimicrobials selected were appropriate, achieved an effective concentration within the bone, and were used for a sufficient duration. Selected patients may benefit from implanted antibiotics, hyperbaric oxygen therapy, revascularization, long-term or intermittent antibiotic administration, or amputation.

Answer 35

ANSWER: E COMMENTS: HAP, HCAP, and VAP are the second most common nosocomial infections after UTI. They result in significant morbidity and mortality. They are due to a wide spectrum of bacterial pathogens and are often polymicrobial, especially in patients with acute respiratory distress syndrome. They are rarely due to viral or fungal agents in immunocompetent patients. Isolation of Candida from endotracheal aspirates of immunocompetent patients usually represents colonization. Common pathogens include aerobic gram-negative bacilli, including P. aeruginosa, E. coli, K. pneumoniae, and Acineto- bacter spp. There has been an emergence of pneumonia associated with gram-positive cocci (S. aureus, particularly MRSA), and it is more commonly seen in diabetics, patients with head trauma, and those hospitalized in the ICU. Infection with anaero- bic organisms may follow aspiration in nonintubated patients but is rare in VAP. Early-onset HAP or VAP occurring within the first 4 days of hospitalization carries a better prognosis than do late-onset infections (5 days or more), which are more likely to be due to multidrug- resistant bacterial pathogens and result in increased morbidity and mortality. Additional risk factors for multidrug-resistant bacterial pathogens such as Pseudomonas, Acinetobacter spp., MRSA, and K. pneumoniae include antimicrobial therapy or hospitalization in the preceding 90 days, a high frequency of antibiotic resistance in the community or in the specific hospital unit, and immunosuppressive disease or therapy. Risk factors for multidrug-resistant pathogens in patients with HCAP include residence in a nursing home or long- term care facility, home infusion therapy, chronic dialysis within 30 days, home wound care, and a family member with a multidrug-resistant pathogen. P. aeruginosa is the most common gram-negative bacterial pathogen that causes multidrug-resistant HAP/VAP, with some iso- lates being susceptible only to polymyxin B. Most MRSA infections are treated successfully with linezolid, although MRSA isolates resistant to linezolid are emerging. Early administration of a broad-spectrum antibiotic in adequate doses and deescalation of the initial antibiotic therapy based on cultures and clinical response are essential. Failure to adequately treat the infection because of delayed initiation of appropriate therapy has been associated with increased mortality. Guidelines have been established by the American Thoracic Society and the Infectious Disease Society of America for empiric therapy in immunocompetent adults with bacterial causes of HAP, VAP, or HCAP; treatment should include either ceftriaxone, a fluoroquinolone, ampicillin/sulbactam, or ertapenem if there is no suspicion of a multidrug-resistant pathogen.

Answer 36

ANSWER: E COMMENTS: Multiple antimicrobial agents are contraindicated in pregnancy. Of the answer choices listed above, erythromycin is the only agent considered safe. Most penicillins and cephalosporins are safe as well. Ganciclovir, ketoconazole, and albendazole are teratogenic in the first trimester. Streptomycin has been shown to cause ototoxicity in fetuses.

Answer 37

C. Louis Pasteur

Answer 38

D. Pioneered Charles McBurney

Answer 39

C. Infection

Answer 40

C. Severe sepsis

Answer 41

D. Eschericia coli

Answer 42

A. Clostridium perfringes

Answer 43

A. Drainage

Answer 44

D. All of the above.

Answer 45

C. Incision and drainage

Answer 46

C. Secondary

Answer 47

A. 14-21 days of antibiotics

Answer 48

C. Cellulitis