Surgical Infections Flashcards
Transferrin plays a role in host defense by
A. Sequestering iron, which is necessary for microbial growth
B. Increasing the ability of fibrinogen to trap microbes
C. Direct injury to the bacterial cell membrane
D. Direct injury to the bacterial mitochondria
Answer: A
Once microbes enter a sterile body compartment (eg, pleural or peritoneal cavity) or tissue, additional host defenses
act to limit and/or eliminate these pathogens.
Initially, several primitive and relatively nonspecific host defenses act to
contain the nidus of infection, which may include microbes as
well as debris, devitalized tissue, and foreign bodies, depending on the nature of the injury.
These defenses include the physical barrier of the tissue itself, as well as the capacity of proteins, such as lactoferrin and transferrin, to sequester the critical microbial growth factor iron, thereby limiting microbial growth.
In addition, fibrinogen within the inflammatory
fluid has the ability to trap large numbers of microbes during the process in which it polymerizes into fibrin.
Within the peritoneal cavity, unique host defenses exist, including a diaphragmatic pumping mechanism whereby particles including microbes within peritoneal fluid arc expunged from the
abdominal cavity via specialized structures on the undersurface of the diaphragm.
Concurrently, containment by the
omentum, the so-called “gatekeeper” of the abdomen and intestinal ileus, serves to wall off infection.
However, the latter
processes and fibrin trapping have a high likelihood of contributing to the formation of an intra-abdominal abscess.
Which is NOT a component of systemic inflammatory response syndrome (SIRS)?
A. Temperature
B. White blood cell (WBC) count
C. Blood pressure
D. Heart rate
Answer: C
Infection is defined by the presence of microorganisms in host tissue or the bloodstream.
At the site of infection the classic findings of rubor, calor, and dolor in areas such as the skin or subcutaneous tissue are common.
Most infections in normal individuals with intact host defenses are associated with these local manifestations, plus systemic manifestations such as elevated temperature, elevated white blood cell (WBC) count, tachycardia, or tachypnea.
The systemic manifestations noted above comprise the systemic inflammatory response syndrome (SIRS).
The best method for hair removal from an operative field is
A. Shaving the night before
B. Depilating the night before surgery
C. Shaving in the operating room
D. Using hair clippers in the operating room
Answer: D
Hair removal should take place using a clipper rather than a razor; the latter promotes overgrowth of skin microbes in small nicks and cuts.
Dedicated use of these modalities clearly
has been shown to diminish the quantity of skin microflora.
(See Schwartz 10th cd.,p. 141.)
A patient with necrotizing pancreatitis undergoes computed tomography (CT)-guided aspiration, which results in growth of Escherichia coli on culture. The most appropriate treatment is
A. Culture-appropriate antibiotic therapy
B. Endoscopic retrograde cholangiopancreatography with sphincterotomy
C. CT-guided placement of drain(s)
D. Exploratory laparotomy
Answer: D
The primary precept of surgical infectious disease therapy
consists of drainage of all purulent material, debridement of
all infected, devitalized tissue, and debris, and/or removal of foreign bodies at the site of infection, plus remediation of the
underlying cause of infection.
A discrete, walled-off purulent fluid collection (ie, an abscess) requires drainage via percutaneous drain insertion or an operative approach in which incision and drainage take place.
An ongoing source of contamination (eg, bowel perforation) or the presence of an
aggressive, rapidly spreading infection (eg, necrotizing soft
tissue infection) invariably requires expedient, aggressive operative intervention, both to remove contaminated material and infected tissue (eg, radical debridement or amputation) and to remove the initial cause of infection (eg, bowel resection).
Which factor does NOT influence the development of surgical site infections (SSIs)?
A. Duration of procedure
B. Degree of microbial contamination of the wound
C. Malnutrition
D. General anesthesia
Answer: D
Surgical site infections (SSIs) are infections of the tissues, organs, or spaces exposed by surgeons during performance of an invasive procedure.
SSIs are classified into incisional and
organ/space infections, and the former are further subclassified into superficial (limited to skin and subcutaneous tissue)
and deep incisional categories.
The development of SSIs is related to three factors: (1) the degree of microbial contamination of the wound during surgery,
(2) the duration of the
procedure, and
(3) host factors such as diabetes, malnutrition,
obesity, immune suppression, and a number of other underlying disease states.
During a laparoscopic appendectomy, a large bowel injury was caused during trochar placement with spillage of bowel contents into the abdomen. What class of surgical wound is this?
A. Class I (clean)
B. Class II (clean/contaminated)
C. Class III (contaminated)
D. Class IV (dirty)
Answer: C
Surgical wounds are classified based on the presumed magnitude of the bacterial load at the time of surgery.
Clean wounds (Class I) include those in which no infection is present; only skin microflora potentially contaminate the wound, and no hollow viscus that contains microbes is entered.
Class ID wounds are similar except that a prosthetic device (eg, mesh or valve) is inserted.
Clean/contaminatcd wounds (Class II) include those in which a hollow viscus, such as the respiratory, alimentary, or genitourinary tracts, with indigenous bacterial flora is opened under controlled circumstances without significant spillage of contents.
Contaminated wounds
(Class III) include open accidental wounds encountered early after injury, those with extensive introduction of bacteria into a normally sterile area of the body due to major breaks
in sterile technique (eg, open cardiac massage), gross spillage of viscus contents such as from the intestine, or incision
through inflamed, albeit nonpurulent, tissue.
Dirty wounds (Class IV) include traumatic wounds in which a significant delay in treatment has occurred and in which necrotic tissue is present, those created in the presence of overt infection as
evidenced by the presence of purulent material, and those
created to access a perforated viscus accompanied by a high
degree of contamination.
The most appropriate treatment of a 4-cm hepatic abscess is
A. Antibiotic therapy alone
B. Aspiration for culture and antibiotic therapy
C. Percutaneous drainage and antibiotic therapy
D. Operative exploration, open drainage of the abscess,
and antibiotic therapy
Answer: C
Hepatic abscesses are rare, currently accounting for approximately 15 per 100,000 hospital admissions in the United States.
Pyogenic abscesses account for approximately 80% of eases, the remaining 20% being equally divided among parasitic and fungal forms.
Formerly, pyogenic liver abscesses were caused
by pyelophlebitis due to neglected appendicitis or diverticulitis.
Today, manipulation of the biliary tract to treat a variety of diseases has become a more common cause, although in nearly
50% of patients no cause is identified.
The most common aerobic bacteria identified in recent series include E. coli, Klebsiella pneumoniae, and other enteric bacilli, enterococci, and
Pseudomonas spp., while the most common anaerobic bacteria are Bacteroides spp., anaerobic streptococci, and Fusobacterium spp.
Candida albicans and other similar yeasts cause the majority of fungal hepatic abscesses.
Snail (<1 cm), multiple
abscesses should be sampled and treated with a 4- to 6-week course of antibiotics.
Larger abscesses invariably are amenable to percutaneous drainage, with parameters for antibiotic therapy and drain removal similar to those mentioned above.
Splenic abscesses are extremely rare and are treated in a similar fashion.
Recurrent hepatic or splenic abscesses may require operative intervention—unroofing and marsupialization or
splenectomy, respectively.
Postoperative urinary tract infections (UTIs)
A. Are usually treated with a 7- to 10-day course of antibiotics.
B. Initial therapy should be directed by results of urine culture.
C. Are established by >104 CFU/mL of bacteria in urine culture in asymptomatic patients.
D. Can be reduced by irrigating indwelling Foley catheters daily.
Answer: B
The presence of a postoperative UTI should be considered based on urinalysis demonstrating WBCs or bacteria, a positive test for leukocyte esterase, or a combination of these elements. The diagnosis is established after >104 CFU/mL of microbes are identified by culture techniques in symptomatic patients, or > 10s CFU/mL in asymptomatic individuals.
Treatment for 3 to 5 days with a single antibiotic directed against
the most common organisms (eg, E. Coli, K. pneumoniae) that
achieves high levels in the urine is appropriate.
Initial therapy is directed by Gram’s stain results and is refined as culture results become available.
Postoperative surgical patients should have indwelling urinary catheters removed as quickly as possible, typically within 1 to 2 days, as long as they are
mobile, to avoid the development of a UTI.
The first step in the evaluation and treatment of a patient
with an infected bug bite on the leg with cellulitis, bullae, thin grayish fluid draining from the wound, and pain out
of proportion to the physical findings is
A. Obtain C-reactive protein
B. CT scan of the leg
C. Magnetic resonance imaging (MRI) of the leg
D. Operative exploration
Answer: D
The diagnosis of necrotizing infection is established solely
upon a constellation of clinical findings, not all of which are present in every patient.
Not surprisingly, patients often develop sepsis syndrome or septic shock without an obvious cause.
The extremities, perineum, trunk, and torso are most commonly affected, in that order.
Careful examination should be undertaken for an entry site such as a small break or sinus in the skin from which grayish, turbid semipurulent
material (‘dishwater pus”) can be expressed, as well as for the presence of skin changes (bronze hue or brawny induration),
blebs, or crepitus.
The patient often develops pain at the site
of infection that appears to be out of proportion to any of the physical manifestations.
Any of these findings mandates immediate surgical intervention, which should consist of
exposure and direct visualization of potentially infected tissue (including deep soft tissue, fascia, and underlying muscle) and radical resection of affected areas.
Radiologic studies should
be undertaken only in patients in whom the diagnosis is not seriously considered, as they delay surgical intervention and
frequently provide confusing information.
Unfortunately, surgical extirpation of infected tissue frequently entails amputation and/or disfiguring procedures; however, incomplete
procedures arc associated with higher rates of morbidity and mortality.
What is FALSE regarding intravascular catheter
infections?
A. Selected low-virulence infections can be treated with
a prolonged course of antibiotics.
B. In high-risk patients, prophylactic antibiotics infused through the catheter can reduce rate of catheter infections.
C. Bacteremia with gram-negative bacteria or fungi should prompt catheter removal.
D. Many patients with intravascular catheter infections are asymptomatic.
Answer: B
Many patients who develop intravascular catheter infections
are asymptomatic, often exhibiting solely an elevation in the
WBC count.
Blood cultures obtained from a peripheral site
and drawn through the catheter that reveal the presence of the same organism increase the index of suspicion for the presence of a catheter infection.
Obvious purulence at the exit site of the skin tunnel, severe sepsis syndrome due to any type of
organism when other potential causes have been excluded, or
bacteremia due to gram-negative aerobes or fungi should lead to catheter removal.
Selected catheter infections due to low-virulence microbes such as Staphylococcus epidermidis can be effectively treated in approximately 50 to 60% of patients with a 14- to 21-day course of an antibiotic, which should be considered when no other vascular access site exists.
Use of systemic antibacterial or antifungal agents to prevent catheter infection is of no utility and is contraindicated.
Patients with a penicillin allergy are LEAST likely to have a cross-reaction with
A. Synthetic penicillins
B. Carbapenems
C. Cephalosporins
D. Monobactams
Answer: D
Allergy to antimicrobial agents must be considered prior to
prescribing them.
First, it is important to ascertain whether a patient has had any type of allergic reaction in association with administration of a particular antibiotic.
However, one
should take care to ensure that the purported reaction consists of true allergic symptoms and signs, such as urticaria,
bronchospasm, or other similar manifestations, rather than indigestion or nausea.
Penicillin allergy is quite common, the reported incidence ranging from 0.7 to 10%. Although avoiding the use of any beta-lactam drug is appropriate in patients
who manifest significant allergic reactions to penicillins, the incidence of cross-reactivity appears low for all related agents, with 1% cross-reactivity for carbapcncms, 5 to 7%
cross-reactivity for cephalosporins, and extrdtnely small or
nonexistent cross-reactivity for monobactams.
What is the estimated risk of transmission of human immunodeficiency virus (HIV) from a needlestick from a source with HIV-infected blood?
A. <0.5%
B. 1%
C. 5%
D. 10%
Answer: A
While alarming to contemplate, the risk of human immunodeficiency virus (HIV) transmission from patient to surgeon
is low.
As of May 2011, there had been six cases of surgeons with HIV seroconversion from a possible occupational exposure, with no new cases reported since 1999.
Of the numbers
of health care workers with likely occupationally acquired HIV infection (n = 200), surgeons were one of the lower risk
groups (compared to nurses at 60 cases and nonsurgeon physicians at 19 cases).
The estimated risk of transmission from
a needlestick from a source with HIV-infected blood is estimated at 0.3%.
Closure of an appendectomy wound in a patient with perforated appendicitis who is receiving appropriate antibiotics will result in a wound infection in what percentage of patients?
A. 3-4%
B. 8-12%
C. 15-18%
D. 22-25%
Answer: A
Surgical management of the wound is also a critical determinant of the propensity to develop an SSI.
In healthy individuals, class I and II wounds may be closed primarily, while skin closure of class III and IV wounds is associated with high rates of incisional SSIs (~25-50%).
The superficial aspects of these latter types of wounds should be packed open and allowed to heal by secondary intention, although selective use of delayed primary closure has been associated with a reduction in incisional SSI rates.
It remains to be determined whether National Nosocomial Infections Surveillance (NNIS) system type stratification schemes can be employed prospectively in order to target specific subgroups of patients who will benefit from the use of prophylactic antibiotic and/or specific wound management techniques.
One clear example based on cogent data from clinical trials is that class III wounds in healthy patients undergoing appendectomy for perforated or gangrenous appendicitis can be primarily closed as long as antibiotic therapy directed against aerobes and anaerobes is administered.
This practice leads to SSI rates of approximately 3 to 4%.
A chronic carrier state occurs with hepatitis C infection
A. 90-99%
B. 75-80%
C. 50-60%
D. 10-30%
Answer: B
Hepatitis C virus (HCV), previously known as non-A, non-B hepatitis, is an RNA flavivirus first identified specifically in the late 1980s.
This virus is confined to humans and chimpanzees.
A chronic carrier state develops in 75 to 80% of patients with the infection, with chronic liver disease occurring in three-fourths of patients who develop chronic infection. The number of new infections per year has declined since the 1980s due to routine testing of blood donors for this virus.
Fortunately, HCV is not transmitted efficiently through occupational exposures to blood, with the seroconversion rate after accidental needlestick approximately 1.8%.
Possible exposure to anthrax should be initially treated with
A. Colistin
B. Ciprofloxacin or doxycycline
C. Amoxicillin
D. Observation
Answer: B
Inhalational anthrax develops after a 1- to 6-day incubation period, with nonspecific symptoms including malaise, myalgia, and fever.
Over a short period of time, these symptoms worsen, with development of respiratory distress, chest pain, and diaphoresis.
Characteristic chest roentgenographic findings include a widened mediastinum and pleural effusions.
A key aspect in establishing the diagnosis is eliciting an exposure history.
Rapid antigen tests are currently under development for identification of this gram-positive rod.
Postexposure prophylaxis consists of administration of either ciprofloxacin or doxycycline.
If an isolate is demonstrated to be penicillin-sensitive, the patient should be switched to amoxicillin.
Inhalational exposure followed by the development of symptoms is associated with a high mortality rate.
Treatment options include combination therapy with ciprofloxacin, clindamycin, and rifampin; clindamycin added to blocks production of toxin, while rifampin penetrates into the central nervous system and intracellular locations.
The most effective postexposure prophylaxis for a surgeon stuck with a needle while operating on an HIV-positive patient is
A. None (no effective treatment is known).
B. Two- or three-drug therapy started within hours of exposure.
C. Single drug therapy started within 24 hours of exposure.
D. Triple drug therapy started within 24 hours of exposure.
Answer: B
Postexposure prophylaxis for HIV has significantly decreased the risk of seroconversion for health care workers with occupational exposure to HIV.
Steps to initiate postexposure prophylaxis should be initiated within hours rather than days for the most effective preventive therapy.
Postexposure prophylaxis with a two- or three-drug regimen should be initiated for health care workers with significant exposure to patients with an HIV-positive status.
If a patient’s HIV status is unknown, it may be advisable to begin postexposure prophylaxis while testing is carried out, particularly if the patient is at high risk for infection due to HIV (eg, intravenous narcotic use).
Generally, postexposure prophylaxis is not warranted for exposure to sources with unknown status, such as deceased persons or needles from a sharps container.
What is NOT an early goal in treatment of severe sepsis?
A. Mean arterial pressure >65 mm Hg
B. Central venous pressure 8 to 12 mm
C. Urine output >0.5 cc/kg/h
D. Serum lactate <2 mmol/L
Answer: D
Patients presenting with severe sepsis should receive resuscitation fluids to achieve a central venous pressure target of 8 to 12 mm Hg, with a goal of mean arterial pressure of >65 mm Hg
and urine output of >0.5 cc/kg/h.
Delaying this resuscitative step for as little as 3 hours until arrival in the ICU has been shown to result in poor outcome.
Typically this goal necessitates early placement of central venous catheter.
A patient in the ICU has been on ventilator support for 3 weeks. He has new onset elevated WBC count, fever, and consolidation seen on chest X-ray.
What is an appropriate next step?
A. Exchange endotracheal tube and change respiratory circuit.
B. Obtain bronchoalveolar lavage.
C. Start treatment with empiric penicillin G.
D. Obtain chest CT.
Answer: B
Prolonged mechanical ventilation is associated with nosocomial pneumonia.
These patients present with more severe disease, are more likely to be infected with drug-resistant pathogens, and suffer increased mortality compared with patients who develop community-acquired pneumonia.
The diagnosis of pneumonia is established by presence of a purulent sputum, elevated leukocyte count, fever, and new chest X-ray abnormalities such as consolidation.
The presence of two of the clinical findings, plus chest X-ray findings, significantly increases the likelihood of pneumonia.
Consideration should be given to performing bronchoalveolar lavage to obtain samples for Gram stain and culture.
Some authors advocate quantitative cultures as a means to identify a threshold for diagnosis.
Surgical patients should be weaned from mechanical ventilation as soon as feasible, based on oxygenation and inspiratory effort, as prolonged mechanical ventilation increases the risk of nosocomial pneumonia.
Patients with severe, necrotizing pancreatitis should be treated with
A. No antibiotics unless CT-guided aspiration of the area yields positive cultures
B. Empiric cefoxitin or cefotetan
C. Empiric cefuroxime plus gentamicin
D. Empiric carbapenems or fluoroquinolones
Answer: D
Current care of patients with severe acute pancreatitis includes staging with dynamic, contrast-enhanced helical CT scan with 3-mm tomographs to determine the extent of
pancreatic necrosis, coupled with the use of one of several prognostic scoring systems.
Patients who exhibit significant pancreatic necrosis should be carefully monitored in the ICU and undergo follow-up CT examination. The weight of current evidence also favors administration of empiric antibiotic therapy to reduce the incidence and severity of secondary
pancreatic infection, which typically occurs several weeks after the initial episode of pancreatitis.
Several randomized, prospective trials have demonstrated a decrease in the rate of
infection and mortality using agents such as carbapenems or
fluoroquinolones that achieve high pancreatic tissue levels.
A patient with a localized wound infection after surgery should be treated with
A. Antibiotics and warm soaks to the wound
B. Antibiotics alone
C. Antibiotics and opening the wound
D. Incision and drainage alone
Answer: D
Effective therapy for incisional SSIs consists solely of incision and drainage without the addition of antibiotics.
Antibiotic therapy is reserved for patients in whom evidence of severe
cellulitis is present, or who manifest concurrent sepsis syndrome.
The open wound often is allowed to heal by secondary intention, with dressings being changed twice a day.
The use of topical antibiotics and antiseptics, to further wound healing, remains unproven, although anecdotal studies indicate their potential utility in complex wounds that do not heal with
routine measures.
Which areas likely do NOT contain resident
microorganisms?
A. Terminal ileum
B. Oropharynx
C. Main pancreatic duct
D. Nares
Answer: C
The urogenital, biliary, pancreatic ductal, and distal respiratory tracts do not possess resident microflora in healthy
individuals, although microbes may be present if these barriers are affected by disease (eg, malignancy, inflammation,
calculi, or foreign body), or if microorganisms are introduced from an external source (eg, urinary catheter or pulmonary aspiration).
In contrast, significant numbers of microbes are
encountered in many portions of the gastrointestinal tract,
with vast numbers being found within the oropharynx and
distal colorectum, although the specific organisms differ.
On the eighth day after an exploratory laparotomy and bowel resection complicated by intraabdominal hypertension, a 65-year-old female who remains intubated in the intensive care unit (ICU) develops a fever of 102°F. An infectious workup reveals a new right lower lobe consolidation. When initiating antibiotic therapy for presumed ventilator-associ- ated pneumonia (VAP), which of the following does not treat Pseudomonas aeruginosa?
A. Cefepime
B. Unasyn (ampicillin/sulbactam)
C. Ticarcillin
D. Aztreonam
E. Ciprofloxacin
ANSWER: B
P. aeruginosa is a gram-negative bacillus commonly implicated in VAP.
Antipseudomonal antibiotics should be initiated empirically in any patient with VAP prior to isolation of the organism on culture due to the high mortality associated with pseudomonal infection.
Antipseudomonal penicillins include ticarcillin and piper- acillin. Third- and fourth-generation cephalosporins, such as ceftazidime and cefepime, are effective against P. aeruginosa and have a relatively narrow range of activity, making them preferred agents in susceptible isolates.
Monobactams (like aztreonam) and carbapenems (meropenem, imipenem) are effective, but have a very broad spectrum of activity, and should be deescalated once susceptibilities are available.
Fluoroquinolones are also effective. The polymyxin colistin is also effective, but has an extensive toxicity profile, and should be used cautiously with multiresistant organisms.
A 67-year-old male remains in the hospital 1 week after undergoing a pancreaticoduodenectomy.
He has two intraabdominal closed-suction drains in place, as well as a left internal jugular triple lumen catheter; his Foley catheter was removed on the third postoperative day.
On the seventh postoperative day, he becomes febrile to 101.5°F, and a fever workup reveals a growth of Enterococcus in two of two peripheral blood cultures.
Which of the following is true regarding the diagnosis of a central line–associated bloodstream infection (CLABSI)?
A. It is preferential to begin empiric antimicrobial therapy prior to obtaining cultures.
B. Catheter-site exudate, if present, should not be cultured when there is concern for a line-related bloodstream infection.
C. The subcutaneous portion of the central venous catheter should be cultured, rather than the tip.
D. Paired blood samples (one from the catheter and one from a peripheral vein, or alternatively from greater than two lumens of the same central venous catheter) growing the same organism at levels that meet catheter-related bloodstream infection criteria are required to diagnose a CLABSI.
E. Growth of greater than 10 colony-forming units (cfu) by semiquantitative (roll-plate) culture confirms catheter colonization.
D
Which of the following is true regarding the treatment of catheter-related bloodstream infections?
A. All catheters in cases of confirmed CLABSI should be removed; it is never appropriate to attempt to salvage the infected catheter.
B. Empiric coverage of Candida should be initiated in bone marrow or solid organ transplant patients with presumed CLABSI.
C. Empiric antibiotic therapy should include methicillin- resistant Staphylococcus aureus (MRSA) coverage as well as gram-negative rod (GNR) coverage, regardless of the severity of illness.
D. Duration of antibiotic therapy in CLABSIs is timed from the day when empiric antibiotics were initiated.
E. The location of a temporary central venous catheter (subclavian versus internal jugular versus femoral) has no influence on the empiric antibiotic agents that should be used.
B
COMMENTS: Central venous catheters are commonly used in many settings in modern health care, but their use is associated with the risk of bloodstream infections, known as CLABSIs. These infections are known to increase morbidity, mortality, and health care costs.
To diagnose a CLABSI, growth of greater than 15 cfu by semiquantitative (roll-plate) culture from at least two samples is required; these two samples may be obtained from the catheter and a peripheral vein or, alternatively, from at least two lumens from the same central venous catheter.
The diagnosis of CLABSI is best defined by a colony count threefold greater than that obtained from a peripheral vein. Skin and catheter hubs should be prepared with alcohol, tincture of iodine, or alcohol-based chlorhexidine (>0.5%) with adequate drying time, prior to obtaining cultures; cultures should be obtained by trained phlebotomists if possible.
Management of CLABSI varies based on the organism cultured and the severity of illness, but for all CLABSIs, the duration of antimicrobial therapy is determined on the first day of obtaining negative blood cultures.
Preferably, adequate cultures are obtained prior to the initiation of antibiotic therapy.
Empiric therapy in uncomplicated cases [i.e., cases without evidence of severe sepsis, endocarditis or osteomyelitis (OM), or without evidence of infection of the catheter tunnel or adjacent abscess] should begin with antibiotics that cover gram-positive cocci.
Vancomycin or daptomycin for empiric therapy should be reserved for areas with a high prevalence of MRSA. Empiric GNR coverage should be added in cases of severe sepsis, neutropenia, in patients with known colonization with a GNR organism, or in patients with femoral catheters.
Empiric coverage for Candida, either with an echinocandin or a fluconazole, should be initiated in patients with severe sepsis plus prolonged broad-spectrum antibiotic use, total parenteral nutrition, hematologic malignancy or receipt of solid organ or bone marrow transplants, or known Candida colonization.
In most circumstances, the infected catheter should be removed; however, there are certain instances in which salvage of the catheter may be attempted.
Antibiotic locks (antibiotic solutions that are instilled into the catheter itself) can be used in conjunction with systemic antimicrobial therapy, particularly in patients in whom catheters are difficult to remove or replace (i.e., tunneled hemodialysis catheters or ports for parenteral nutrition in short gut syndrome).
If patients have persistent positive blood cultures after salvage attempt, the catheter should be removed.
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.
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.
A 57-year-old Asian American female presents to her hepatologist’s office for monitoring of her known chronic hepatitis B infection. Which of the following sets of test results is consistent with chronic active hepatitis B infection?
A. Hepatitis B surface antigen (HBsAg)+ less than 6 months, hepatitis B surface antibody (HBsAb)−, immunoglobulin M (IgM) anti-HBc+, elevated aspartate transaminase (AST), and alanine transaminase (ALT)
B. HBsAg+ greater than 6 months, HBsAb−, HBcAb+, hepatitis B virus (HBV) DNA > 20,000 IU/mL, mildly elevated AST and ALT
C. HBsAg+ greater than 6 months, hepatitis B e antigen (HBeAg)−, HBV DNA < 2000 IU/mL, normal AST and ALT
D. HBsAg−, HBsAb+, HBcAb+, normal AST and ALT
E. HBsAg−, HBsAb+, HBcAb−, normal AST and ALT
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.
Match the antibiotic and its classical toxicity profile.
A. Vancomycin
B. Aminoglycosides
C. Isoniazid (INH)
D. Fluoroquinolones
E. Tetracycline
a. Tendinopathy
b. Red man syndrome
c. Phototoxicity
d. Hepatitis
e. Ototoxicity
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.
Which of the following is not a Surgical Care Improvement Project (SCIP) measure for infection prevention in surgical patients?
A. The optimal timing for administration of prophylactic antibiotics is within 1 h of surgical incision.
B. Prophylactic antibiotics should be discontinued within 24 h of the end of surgery; in cardiac surgery, this is lengthened to 48 h.
C. Clippers are preferred to razors for preoperative hair removal, if necessary.
D. Goal blood glucose in the first 48 h following surgery is less than 160 mg/dL.
E. Patients should remain normothermic within the first hour following surgery.
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.
Match the surgical procedure with the most appropriate preoperative prophylactic antibiotic.
A. Elective laparoscopic cholecystectomy
B. Femoral to popliteal arterial bypass with graft
C. Cystoscopy with ureteral stent placement
D. Right hemicolectomy
E. Parotidectomy
a. Ertapenem
b. Clindamycin
c. None
d. Cefazolin
e. Ciprofloxacin
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).
A 68-year-old female has been admitted to the emergency room with recurrent Clostridium difficile colitis. Her first episode of C. difficile colitis was 3 months prior after receiving clindamycin for a mild episode of cellulitis. Two months ago, she had a second episode, treated again with full symptom resolution. On examination, her vital signs are normal and her abdomen is benign, with only mildly tender to deep palpation in the right lower quadrant. Laboratory results are notable for a leukocytosis of 13.4,000 cells per MCL with 86% neutrophils, mild hypokalemia, and positive C. difficile stool antigen. An abdominal film shows a colon of normal caliber. What is the most appropriate treatment for this patient?
A. Oral metronidazole 500 mg every 8 h for 10 to 14 days
B. Intravenous (IV) metronidazole 500 mg every 8 h for 10 to 14 days
C. Oral vancomycin 125 mg every 6 h for 10 to 14 days
D. Oral vancomycin, in a tapered and pulsed fashion over approximately 5 to 7 weeks
E. IV vancomycin 125 mg every 6 h for 10 to 14 days
D
The patient in the question above is admitted and started on antibiotics, but her condition continues to deteriorate clinically over the next 2 days despite appropriate antibiotic therapy, probiotics, and supportive treatment. Her white blood cell (WBC) count continues to rise to 17.8 and creatinine increases to 1.5 from baseline of 0.8. She has a low-grade fever and marginal urine output, and her abdomen becomes distended, tympanic, and tender. An abdominal obstructive series shows dilation of the entire colon to 10 cm in diameter without evidence of pneumoperitoneum. Which of the following is not an acceptable course of action in treating severe C. difficile colitis?
A. Transitioning from pulsed to standard scheduled oral vancomycin 125 mg every 6 h with the addition of IV metronidazole 500 mg every 8 h
B. Transitioning from pulsed to standard scheduled oral vancomycin 125 mg every 6 h with the addition of oral fidaxomicin 200 mg every 12 h
C. Subtotal colectomy
D. Diverting loop ileostomy with colonic lavage
E. Metronidazole enemas
E
Which of the following is true regarding the pathophysiology
of C. difficile infection?
A. Antimicrobial agents with activity against C. difficile are equally as likely to result in C. difficile colitis as those without activity against C. difficile.
B. A patient’s inability to produce antibody to toxin A is a significant predictor of recurrent C. difficile infection.
C. Advanced age is not considered a risk factor for develop- ment of clinical C. difficile infection.
D. Studies have suggested that gastric acid suppression [i.e., use of proton pump inhibitors (PPIs) or H2 blockers] may be protective against the development of C. difficile infection.
E. Alcohol-based hand sanitizers are effective in removing C. difficile spores after contact with an infected patient.
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
