Infections and Antimicrobial Therapy

Question 1

In a surgical patient exhibiting signs of a hospital-acquired infection (HAI), be able to develop a differential diagnosis and a plan to assess presence or absence of each infection.

Answer 1

• Catheter-associated urinary tract infection (CAUTI)
• Central line–associated blood stream infection (CLABSI)
• Ventilator-associated pneumonia (VAP)
• Clostridium difficile
• Surgical site infection (SSI; reviewed in a separate module)

Question 2

CAUTI most common organisms?

Answer 2

gram-negative rods and Enterococcus species

Question 3

CLABSI most common organisms

Answer 3

Staphylococcus aureus, Enterococcus, and Candida species (if total parenteral nutrition and intensive care unit [ICU])

Question 4

Hospital-acquired pneumonia/VAP most common organisms

Answer 4

gram-negative bacilli and gram-positive cocci; methicillin-resistant S aureus(MRSA) in patients with prolonged hospitalization and/or prior antibiotic exposure

Question 5

Be able to state measures taken to reduce the incidence of HAI in surgical patients.

Answer 5

• Sterile techniques for placements of CVLs and Foleys
• Daily assessment of the need for indwelling devices
• Preoperative antibiotics for reduction of SSI
• Handwashing
• Care bundles and daily catheter care plans, which reduce the risk of CAUTIs and CLABSIs
• Antibiotic-coated CVLs: may reduce incidence of CLABSIs
• VAP bundles in the ICU (elevation of the head of the bed, sedation vacation with daily weaning assessment, chlorhexidine mouth care, subglottic drainage)
• Hospital-wide antibiotic stewardship programs, which help with decreased rate of infections

Question 6

Be able to recognize that pneumonia in an intubated patient has a subtle presentation and be able to perform an examination and order appropriate testing to confirm or rule out a pneumonia.

Answer 6

• Increase in oxygen demand (rising fraction of inspired oxygen [FiO2] or increased positive-end expiratory pressure [PEEP])
• Increase in volume of secretions and change in quality to purulent
• Leukocytosis, fever, tachypnea, and dyspnea if not intubated
• New or progressive infiltrate on chest x-ray
• Sputum specimen obtained by blind suctioning versus a directed bronchoalveolar lavage, which should have 105organisms/mL to be considered positive

Question 7

Given a patient with a urinary catheter, new onset of fever, leukocytosis, and flank pain, be able to make the diagnosis of CAUTI.

Answer 7

CAUTI diagnosis should be supported with urine culture with 100,000 CFU/mL of pathogens, because urinary catheters can become colonized and give a false-positive result.

Fungal cultures from urine are usually a colonization. Treatment with antifungals should be reserved only for immunocompromised patients and patients with two sites of positive fungal cultures.

Question 8

Be able to define CLABSI and know the diagnostic criteria.

Answer 8

Presence of bloodstream infection and demonstration that the infection is related to the catheter

Must be suspected in patients with central line and fever, leukocytosis, and evidence of sepsis with organ dysfunction

Preferable to obtain peripheral blood cultures rather than from suspected catheter only

Question 9

Be able to recognize the signs and symptoms of C difficile infection.

Answer 9

• Fever, abdominal distention, with or without tenderness, and copious diarrhea may occur. Note that most cases of diarrhea in the ICU are not due to C difficile but rather to the use of sorbitol-containing elixirs, enteral tube feeds, and malabsorption.
• Ileus and constipation may be presenting findings.
• The patient’s condition can progress to septic shock and organ failure that will require emergent colectomy.
• Confirmatory testing should be done using polymerase chain reaction in appropriate clinical settings.

Question 10

Be able to start appropriate treatment of nosocomial infections - VAP.

Answer 10

Start empiric antibiotics against most commonly encountered VAP pathogens (ie, MRSA, Serratia, Pseudonomas, Acinetobacter, Citrobacter, and Enterobacter), as directed by culture data.

Once culture data are available, patients should be treated for 7 days.

Antibiotic duration should be extended only if clinical response is not adequate.

Question 11

How do you treat C diff infections?

Answer 11

Treat C difficile infections with oral vancomycin. However, in patients with a nonfunctional gastrointestinal tract, intravenous metronidazole or vancomycin enemas are suitable alternatives.

In critically ill patients with C difficile colitis, consider the need for operative intervention if there is no clinical response once maximal treatment has started.

Question 12

How do you treat CLABSI?

Answer 12

For suspected CLABSIs, direct antibiotic coverage of Staphylococcus and gram-negative bacteria.

Question 13

Be able to understand the cost to the patient and hospital of HAIs.

Answer 13

• HAIs are associated with increased length of stay, morbidity, mortality, hospital cost, antibiotic resistance, and chronic illness.
• The financial cost associated with HAIs is estimated to be at $5.7 to $6.8 billion each year, as reported by the Centers for Disease Control and Prevention, with SSIs being the most costly.
• Rates of HAI are currently being reported for hospitals and will affect hospital and physician compensations for patient care.

Question 14

Be able to recognize the benefits of an antibiotic stewardship program.

Answer 14

• The benefits include decreased development of resistant organisms, reduced nephrotoxicity, decreased C difficile risk, decreased opportunistic fungal infections, and reduced costs.
• The program involves a multidiscplinary team approach hospital-wide that includes pharmacists, ICU staff, infectious disease specialists, epidemiologists, and other support staff.

Question 15

A 67-year-old man with mitral valve replacement and a coronary artery bypass graft develops a fever of 39.4ºC on postoperative day 13. This is accompanied by leukocytosis of 19,200/µL. He has been extubated but remains on high-flow oxygen. He is hemodynamically stable. The sternotomy incision site is without evidence of infection. His chest x-ray shows mild pulmonary venous congestion. He has a right internal jugular vein line for dialysis for acute postoperative renal failure, and there is no erythema or purulent discharge at the insertion site. He does not have a urinary catheter. What is the appropriate next step?

Answer 15

• No obvious source of infection in this patient.
• CXR and physical have ruled out PNA and SSI.
• A potential source is the R IJV dialysis line.
• Remove the catheter and send the tip for culture.
• Insert a new catheter, and if an alternative site is not appropriate, exchange the catheter over a wire.
• Consider empiric abx therapy, and tailor it to sensitivities.

Question 16

An 88-year-old man was involved in a motor vehicle crash and was unstable on arrival. He sustained left-sided multiple rib fractures and subsequent pneumothorax. On FAST examination, he was found to have free fluid in the pelvis. He was taken to the operating room for an exploratory laparotomy, splenectomy, and left chest tube insertion. He was transferred to the ICU. On postoperative day 7, it is noted that he has been persistently tachycardic for the past 2 days. His white blood count spiked on postoperative day 9. What is your initial differential and what will you do next?

Answer 16

• Keep in mind the risk factors that keep surgical ICU patients at a higher risk for infection in all critical care settings.
• Understand that all indwelling tubes and devices should be considered breaches in the normal host defense mechanisms and potential points of ingress for bacteria and infection.
• Fever and leukocytosis are not enough to indicate an infectious process in ICU patients. Look for other signs of sepsis causing organ dysfunction including, but not limited to, tachycardia, oliguria, hyperglycemia, new-onset hypoxemia, or feeding intolerance.

Question 17

A 72-year-old man is admitted with 2-day history of nausea, vomiting, abdominal pain, and diarrhea. On examination, he is noted to have tachycardia, fever, and abdominal distention. He recently finished a course of antibiotics for community-acquired pneumonia. What is the initial management of this patient?

Answer 17

• Have a high suspicion of C difficile infection.
• Initially, manage with hemodynamic stability and early administration of metronidazole and vancomycin.
• Identify the need for surgical management in the setting of failed medical management because the risk of mortality increases from C difficile colitis in this patient.
• Be aware that the patient needs to undergo subtotal colectomy and in certain situations, laparotomy with end ileostomy and washout with vancomycin solution in order to preserve the colon.

Question 18

Beta-lactams and cephalosporins require what parameter in terms of antibiotic concentration to kill bacteria?

Answer 18

time above minimum inhibitory concentration (MIC)

Question 19

What concentration parameter do aminoglycosides require to become effective?

Answer 19

Simply higher drug concentration

Question 20

What concentration parameter do quinolones require to be effective?

Answer 20

area under the curve

Question 21

What controllable factors can increase the risk for SSIs?

Answer 21

hypothermia, glucose control, antibiotic prophylaxis, and skin preparation affect the rate of SSIs.

Question 22

Describe the usefulness of fever and leukocytosis in detecting infection in the surgical patient.

Answer 22

Fever and leukocytosis raise the suspicion of a surgical infection and can direct ongoing investigation. While they are frequently present in the setting of infection, they are not very specific. Therapy should not be initiated based on these data in isolation.

Question 23

Describe the presentation of a beta-hemolytic streptococcus in SSIs.

Answer 23

local inflammation, erythema, pain and purulent fluid rich in WBCs

Question 24

Describe the presentation of a Clostridia spp SSI.

Answer 24

lack local inflammation signs, but have pain out of proportion to clinical findings, yielding thin and brackish fluid with no WBCs due to the lytic effect of exotoxin on leukocytes

Question 25

A 60-year-old obese woman with non-insulin-dependent diabetes mellitus presents 1 week after an open right hemicolectomy with a small amount of intraoperative enteric spillage. She presents with fever, an elevated white blood cell count, and an erythematous midline incision draining purulent material. What is your approach to further evaluating this patient?

Answer 25

• This patient has a surgical site infection.
• Risk factors include a clean-contaminated wound, obesity, and diabetes.
• Source control, abx, glucose control.
• Open the wound and obtain cultures. Debride necrotic tissue.

Question 26

A 45-year-old man receiving chemotherapy through a central line presents with fever and concerns over a catheter-related bloodstream infection. How will you further evaluate the patient, and what is your treatment strategy?

Answer 26

• Obtain blood cultures.
• Start pt on broad spec abx, including coverage for gram-positive and gram-negative bacteria.
• The catheter should be removed for gram-negative and fungal infections. Medical tx can be attempted if there is a gram-positive infection.
• It may be necessary to hold chemotherapy.

Question 27

A 25-year-old woman underwent a laparoscopic appendectomy 10 days ago for perforated appendicitis. She presents to the emergency department with nausea, vomiting, fever, and abdominal pain. Her incisions are clean, dry, and healing without evidence of erythema or drainage. What is your approach to this patient?

Answer 27

• Vitals, labs, and cultures should be obtained.
• CT of the abdomen and pelvis w/ IV contrast.
• Suspect intra-abdominal abscess.
• IR drainage and antibiotics if stable.
• OR if peritonitis.

Question 28

A 31-year-old man undergoes a splenectomy following a motor vehicle collision. During the procedure, a small bowel injury is also noted with minimal spillage. The patient does fine and is discharged on postoperative day 6. He presents for follow-up 4 days later with mild erythema and cellulitis around the wound but no drainage or induration. What should be the plan?

Answer 28

• Careful examination is warranted.
• Antibiotics should be started.
• The wound may need to be opened if other findings beyond erythema are identified on physical examination.

Question 29

When a patient presents with a necrotizing skin infection, what should be considered in deciding which types of antibiotics are appropriate for empiric coverage as part of an antibiotic regimen?

Answer 29

In general, empiric treatment of necrotizing infection should consist of agents against gram+, gram-, and anaerobic organisms.

• carbapenem or beta-lactam-beta-lactamase inhibitor
• plus an agent with activity against MRSA (vanc or dapto)
• plus Clindamycin, for its antitoxin effects against toxin-elaborating strains of streptococci and staphylococci
• continued until no further debridement needed, HDS normal; tailored to individual patient circumstances

Question 30

In terms of acquired antibiotic resistance, what is vertical gene transfer?

Answer 30

Following a spontaneous mutation, the gene encoding the mutation is conserved in all the progeny of the cell with the original spontaneous mutation.

Question 31

In terms of antibiotic resistance, what is horizontal gene transfe?.

Answer 31

This is transfer of a gene from one bacteria to another, typically via plasmids. An example is transfer of the mecA gene, which encodes penicillin-binding protein 2a; this has low affinity for beta-lactams and therefore causes methicillin resistance in methicillin-resistant Staphylococcus aureus (MRSA).

Question 32

When faced with an intra-abdominal infection, determine the length of antimicrobial therapy.

Answer 32

The Study to Optimize Peritoneal Infection Therapy (STOP IT) trial evaluated 518 patients randomly assigned to 4 ± 1 days of antibiotics versus 2 days beyond resolution of fever and ileus. No difference in death, surgical site infection, or recurrent intra-abdominal infection was found between the two treatment lengths, but antibiotics were significantly reduced in the 4-day course group.

Question 33

An intubated patient in the ICU develops a fever during the middle of the night after several days on a ventilator. He then develops hypotension and tachycardia with a right lower lung consolidation on chest x-ray. How do you manage this?

Answer 33

• Get blood cultures and endotracheal aspiration. Resuscitate.
• VAP w/ risk factors for MDR and in a unit w/ ≤10 gram- isolates are monotherapy resistant and w/ ≤20 percent MRSA, should receive one agent against Pseudomonas, other GNB, and MSSA.
• Patients with VAP who have risk factors for MDR VAP should receive two agents against P. aeruginosa and other GNB, and one agent with against MRSA.
• De-escalate w/ sensitivities.
• Treat for 7 days.

Question 34

A 22-year-old man is on the ward following open appendectomy. He has been receiving an oral cephalosporin for superficial infection of his skin incision. The wound was opened 1 week ago, and there is no longer any surrounding cellulitis. He has mild diarrhea, and per hospital protocol, the nurse sends a C difficile immunoassay that returns positive. What is the next step in management?

Answer 34

• psx: new 3 loose stools/24 hrs (ideally no bowel reg, hx of abx)
• dx: GDH + toxin; NAAT, do not repeat within 7 days
• contact precautions, private room, wash hands
• tx: PO vanc 125 4x/day x10 days or fidaxomicin; 2nd line flagyl
• complications: fulminant CDI - ileus, shock, or megacolon
  
  • tx: PO or rectal vanc (500 4/d) and IV flagyl 500 TID
  • surgery: subtotal colectomy; can do ileostomy w/ antegrade vanc flushes
• 1st recurrence: tapered vanc or fidaxomicin; rpt for 2nd episode
• multiple recurrences: fecal transplant

Question 35

A 64-year-old otherwise healthy man presents to the emergency department with left lower quadrant abdominal pain. His vital signs are normal, and a computed tomography scan shows diverticulitis with a 4-cm pericolonic abscess. Interventional radiology is called to place a percutaneous drain. How do you manage the rest?

Answer 35

• should improve within 1-2 days
• abx: for either 7-10 days total or 4 days s/p completed drainage
• colonoscopy in 6-8 weeks
• offer elective resection of involved segment w/ anastomosis if recurrent

Question 36

A 56-year-old male presents to the ER with left lower quadrant abdominal pain, nausea and vomiting. What is your approach to managing this patient?

Answer 36

• vitals, labs, exam
• CT w/ IV contrast
• ceft/flagyl vs ertapenem vs zosyn
• possible drain vs surgery
• colonoscopy in 6-8 weeks

Question 37

A 24-year-old female presents to the ED with a 5-day history of right lower quadrant pain, nausea, and vomiting. What is your approach to managing this patient?

Answer 37

• broad ddx in a female
• r/o pregnancy
• ultrasound if suspicious for gyn
• CT if no dx

Question 38

A 63-year-old male is POD#6 status post a colostomy takedown following perforated diverticulitis. He has a slow return of bowel function with only a small bowel movement but now complains of abdominal pain, distention, and nausea. His WBC is 14,000. How will you go about your evaluation and workup of this patient?

Answer 38

• suspect leak vs abscess
• in sepsis, give abx and fluid resuscitation
• determine stability, do exam
• if unstable or peritonitis, go to OR
• if stable, CT w/ IV PO and rectal contrast (water sol)
• if abscess, IR drain
• if uncontained leak, emergently fix in OR w/ ex lap
  
  • unresectable phlegmon - leave drains
  • <1cm leak, healthy tissue, stable - primary repair
  • >1cm - resect w/ proximal diversion vs Hartmann

Question 39

A 72-year-old man has undergone an open infrarenal aortic aneurysm repair. In the postanesthesia care unit, the anesthesiologist informs you that prophylactic antibiotics were not given, as ordered, prior to the case. What do you want to do with respect to postoperative orders?

Answer 39

• ppx abx are optimized if given <1 hr before cut
• ppx abx are useless after 3 hrs of inoculation
• prostheses or grafts should receive abx

Question 40

A 33-year-old male bodybuilder with a history of diabetes has a symptomatic right inguinal hernia. Discuss the operative approach and need for perioperative antibiotic prophylaxis.

Answer 40

• Clean: uninfected wound where no inflammation is encountered and the respiratory, gastrointestinal, or genitourinary tracts are not entered and only the skin and subcutaneous tissue are encountered
• Mesh implant requires ppx abx
• Pt has increased risk for SSI 2/2 DM

Question 41

A 54-year-old woman undergoes an elective open left hemicolectomy for colon cancer. On postoperative day 5, she develops a fever to 38.6ºC and on examination of her abdomen, you note redness surrounding her wound.

Answer 41

• vitals and exam
• if fluctuant - open, explore, drain, debride
• abx - bactrim if not sick; vanc if sick