MKSAP quiz on health care-associated infections

Case 1: Surgical site risk

A 68-year-old man is being evaluated for measures to decrease his risk of acquiring a surgical site infection; he is scheduled for coronary artery bypass graft surgery in 5 weeks for limiting chronic angina despite maximal medical therapy. Medical history includes chronic stable angina, hyperlipidemia, hypertension, and diabetes. Medications are low-dose aspirin, propranolol, isosorbide dinitrate, ranolazine, chlorthalidone, lisinopril, and atorvastatin.

On physical examination, blood pressure is 126/72 mm Hg; all other vital signs are normal. On cardiac examination, an S4 is present. The remainder of the examination is noncontributory.

Which of the following is the most appropriate measure to prevent surgical site infection?

A. Evaluate for Staphylococcus aureus nasal carriage
B. Provide postoperative vancomycin prophylaxis for 7 days
C. Provide preoperative vancomycin prophylaxis
D. Shave patient's chest hair the morning of surgery

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Case 2: Catheter care

An 82-year-old woman is hospitalized with hypotension and volume depletion resulting from gastroenteritis. Medical history is noncontributory, and she takes no medications.

On physical examination, temperature is 36.8 °C (98.3 °F), blood pressure is 92/66 mm Hg, pulse rate is 110/min, and respiration rate is 16/min. The remainder of the examination is unremarkable.

Because of difficulty in inserting a peripheral venous access line, an internal jugular central venous catheter will be placed for volume resuscitation.

Which of the following is the most appropriate measure to prevent catheter-related bloodstream infection in this patient?

A. Assess catheter daily for necessity and potential removal
B. Give one dose of vancomycin after catheter insertion
C. Replace catheter every 7 days
D. Use a small sterile drape when inserting the catheter

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Case 3: Ventilator-associated pneumonia

A 67-year-old woman is evaluated after a diagnosis of ventilator-associated pneumonia. She was transferred to the ICU 3 days ago for respiratory failure secondary to Guillain-Barré syndrome and was intubated. Yesterday, the ventilator-associated pneumonia diagnosis was made and empiric antibiotics were started. Today her antibiotic therapy was de-escalated to oxacillin after her sputum culture grew methicillin-sensitive Staphylococcus aureus. Blood cultures were negative. Her medications are oxacillin and low-molecular-weight heparin; she is also undergoing plasmapheresis.

On physical examination, temperature is 37.6 °C (99.6 °F), blood pressure and pulse rate are normal, and respiration rate is 15/min. Oxygen saturation is 97% breathing 40% FiO2. Pulmonary examination reveals scattered rhonchi.

A chest radiograph shows right middle and lower lobe infiltrates without effusions.

Which of the following is the most appropriate antibiotic management?

A. Continue antibiotic therapy for a total of 7 days
B. Continue antibiotic therapy for a total of 14 days
C. Continue antibiotics until extubation
D. Obtain sputum for Gram stain and culture before stopping antibiotics

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Case 4: Persistent bacteremia

A 72-year-old woman undergoes follow-up evaluation for persistent bacteremia. She was hospitalized 12 days ago with fever and chills, which started abruptly 1 week after a cardiac catheterization procedure. Blood cultures were positive for methicillin-sensitive Staphylococcus aureus, and cefazolin therapy was initiated. Medical history is otherwise noncontributory, and she takes no other medications.

On physical examination, temperature is 38.2 °C (100.8 °F), blood pressure is 116/76 mm Hg, pulse rate is 92/min, and respiration rate is 16/min. A systolic murmur is present and is unchanged from previous examinations. Abdominal examination reveals right upper quadrant tenderness. The remainder of the examination is noncontributory.

Laboratory studies show an alanine aminotransferase level of 53 U/L, aspartate aminotransferase level of 58 U/L, and alkaline phosphatase level of 104 U/L.

Repeated blood cultures are positive for S. aureus.

A transthoracic echocardiogram shows a small aortic valve vegetation. An electrocardiogram is normal.

Which of the following is the most appropriate management?

A. Perform abdominal CT
B. Perform head CT
C. Switch cefazolin to daptomycin
D. Switch cefazolin to vancomycin

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Case 5: Urinary tract infection

A 92-year-old man is hospitalized with a complicated urinary tract infection (UTI). He resides in a nursing home and has a chronic indwelling urinary catheter. In the nursing home, a urinalysis and urine culture were performed for possible UTI, and empiric ciprofloxacin therapy was initiated 1 day before transfer to the hospital. In the emergency department, ciprofloxacin was changed to piperacillin-tazobactam, and blood cultures were obtained. Medical history is notable for dementia, benign prostatic hyperplasia, chronic kidney disease, and recurrent UTIs. Medications are donepezil, memantine, and piperacillin-tazobactam.

On physical examination, temperature is 38.5 °C (101.3 °F), blood pressure is 108/70 mm Hg, pulse rate is 100/min, and respiration rate is 16/min. Suprapubic tenderness is noted, and the urinary catheter is draining cloudy urine. Other examination findings are noncontributory.

Laboratory studies show a leukocyte count of 15,200/µL (15.2 × 109/L) and a serum creatinine level of 1.9 mg/dL (168 µmol/L). Urinalysis reveals leukocytes too numerous to count but no erythrocytes.

Urine culture obtained from the nursing home shows more than 105 colony-forming units of Escherichia coli sensitive to piperacillin-tazobactam, gentamicin, cefepime, and meropenem (resistant to ceftriaxone, ceftazidime, cefotaxime, and ciprofloxacin); it is confirmed to be an extended-spectrum β-lactamase–producing organism. Blood cultures are pending.

No infiltrates are seen on the chest radiograph.

Which of the following is the most appropriate treatment?

A. Add gentamicin
B. Continue piperacillin-tazobactam
C. Switch piperacillin-tazobactam to cefepime
D. Switch piperacillin-tazobactam to meropenem

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Case 6: Evaluation before cystoscopy

A 72-year-old man undergoes preprocedural evaluation. He is scheduled to undergo cystoscopy and possible biopsy in follow-up for a previously diagnosed non–muscle invasive bladder cancer followed by an elective right total hip arthroplasty for chronic hip pain. He is otherwise asymptomatic. Medical history is significant for diabetes mellitus, hypertension, kidney transplantation, and osteoarthritis. Medications are metformin, amlodipine, pravastatin, prednisone, and tacrolimus.

On physical examination, vital signs are normal. External rotation of the right hip elicits pain. The examination is otherwise normal.

On microscopic urinalysis, leukocyte count is 20 to 40/hpf, erythrocyte count is 0 to 1/hpf, 2+ bacteria are present, and no squamous epithelial cells are seen. Urine culture grew 10,000 to 50,000 colony-forming units of Proteus mirabilis.

Kidney ultrasonography is unremarkable.

Which of the following is the primary indication for antimicrobial therapy in this patient?

A. Cystoscopy and biopsy
B. Diabetes mellitus
C. Kidney transplant
D. Total hip arthroplasty

View correct answer for Case 6

Answers and commentary

Case 1

Correct answer: A. Evaluate for Staphylococcus aureus nasal carriage.

The most appropriate measure to prevent surgical site infection is to evaluate for Staphylococcus aureus nasal carriage 2 weeks before surgery and decolonize if positive. S. aureus is the most common pathogen (23%) associated with surgical site infections (SSIs). SSIs after coronary artery bypass graft surgery can be serious and devastating, with mediastinitis related to S. aureus of particular concern. The 2016 World Health Organization guidelines recommend that patients known to be nasal carriers of S. aureus who are scheduled to undergo cardiothoracic or orthopedic surgery should have preoperative decolonization (mupirocin ointment for 5 days with or without chlorhexidine gluconate body wash) to decrease the risk of developing S. aureus–related SSI.

Data do not support extending antibiotic prophylaxis beyond 24 hours after cardiac surgery even while drains remain in place. For most other surgeries, no additional doses of antibiotic should be given postoperatively, even in cases of intraoperative spillage of gastrointestinal contents. Postoperative antibiotics are only indicated when treating an active infection.

Preoperative antibiotic prophylaxis reduces the risk of SSI by decreasing the concentration of pathogens at or around the incision site. The agent used and the timing of administration are key. For cardiac surgery, cefazolin is recommended unless a patient is known to have methicillin-resistant S. aureus colonization or has a severe (anaphylactic) β-lactam allergy, in which case vancomycin is used. For optimal benefit, the antibiotic should be administered 1 to 2 hours before incision. For procedures lasting more than several hours, the antibiotic should be redosed during surgery (for example, redose at 3-4 hours for cefazolin).

Preoperative shaving in the area of the planned incision increases the risk of SSI. Shaving causes microscopic abrasions of the skin, which promotes bacterial proliferation. Recommendations indicate only removing hair from the surgical site if it will interfere with the procedure, in which case clipping is preferred.

Key Point

  • Patients undergoing cardiothoracic or orthopedic surgery should be screened for nasal carriage of Staphylococcus aureus and, if positive, should have preoperative decolonization.

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Case 2

Correct answer: A. Assess catheter daily for necessity and potential removal.

This patient's central venous catheter (CVC) should be assessed daily for continued necessity and potential removal. Approximately 250,000 central line–associated bloodstream infections (CLABSIs) occur in the United States every year, with 80,000 occurring in the ICU. CLABSIs increase length of hospital stay up to 24 days and have an attributable mortality rate of 35%. Approximately 55% of patients in the ICU and 24% of those in other units have a central line. Antimicrobial resistance is a problem for most CLABSI pathogens. The risk of CLABSI can be reduced by routinely incorporating the CVC bundle as part of patient care. The CVC insertion bundle includes hand hygiene; use of full barrier precautions (including a large full-body sterile drape to cover the patient during catheter insertion) and personal protective equipment (mask, cap, sterile gown, and gloves); chlorhexidine skin antisepsis; selection of optimal catheter type (such as selecting the minimum number of ports or lumens needed) and site; sterile dressing; and daily review of line necessity with prompt removal of unnecessary catheters. The daily review of line necessity and documentation can be achieved with multidisciplinary rounds, daily reminders, and automated alerts. These practices are important for decreasing the risk of developing CLABSIs. Just as with the insertion bundle, a maintenance bundle helps decrease the risk of introducing organisms during use of the catheter. Components of the maintenance bundle include daily review of line necessity with prompt removal of unnecessary catheters, hand hygiene before manipulation of the intravenous system, care of injection ports, and proper monitoring of catheter site dressing and dressing changes.

Guidelines recommend against routinely replacing CVCs (or arterial catheters) and administering antimicrobial prophylaxis for short-term or tunneled catheter insertion. Neither practice has been shown to decrease central line–associated infections. In fact, routinely changing central catheters may increase the risk of infection by introducing bacteria from the skin at the time of insertion.

Key Point

  • Central venous catheters should be assessed daily for continued necessity and removed promptly when they are no longer needed.

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Case 3

Correct answer: A. Continue antibiotic therapy for a total of 7 days.

The recommended treatment duration for ventilator-associated pneumonia (VAP) is 7 days. VAP is defined as pneumonia developing 48 hours after endotracheal intubation. The most significant VAP risk factor is intubation and mechanical ventilation. Early onset (<5 days after hospitalization or intubation) generally results from antimicrobial-sensitive organisms (Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, and antibiotic-susceptible gram-negative bacteria); late onset (≥5 days after hospitalization or intubation) is more likely with multidrug-resistant organisms (MDROs), including Pseudomonas aeruginosa, Klebsiella pneumoniae, Acinetobacter species, Stenotrophomonas maltophilia, Burkholderia cepacia, and methicillin-resistant S. aureus. The recommended therapy duration for VAP is 7 days. A longer antibiotic duration does not improve outcomes, leads to the emergence of antibiotic-resistant organisms, and can increase the risk for adverse effects from antibiotic exposure.

Sputum Gram stain and culture are unnecessary for influencing the timing to stop antibiotics; the implicated organism may remain (colonizing) after treatment has been completed and the patient has improved clinically. Persistence of the infecting organism is not an indication to continue antibiotic therapy.

Antibiotics should not be continued until extubation. The antibiotic therapy duration is the same for patients who are successfully extubated during treatment and patients who remain intubated after 7 days of antibiotic therapy as long as clinical improvement occurs. If the patient does not improve clinically (resolution of fever, decrease in oxygenation and suction requirements) or initially improves and then worsens during treatment, the patient should be evaluated to identify development of infectious complications (pleural effusion, empyema, superinfection, antibiotic resistance) or noninfectious complications.

Key Point

  • Ventilator-associated pneumonia should be treated with a 7-day course of antibiotics; longer courses contribute to the emergence of antibiotic resistance, increase the risk for antibiotic-related adverse effects, and do not improve outcomes.

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Case 4

Correct answer: A. Perform abdominal CT.

An abdominal CT is the most appropriate next step in the evaluation and management of this patient. Bacteremia persisting more than 72 hours after the start of appropriate antimicrobial therapy suggests a complicated infection, requiring additional evaluation with a longer treatment course. Endocarditis and vertebral osteomyelitis are two important complications of Staphylococcus aureus bacteremia. Patients with abdominal pain or flank pain should undergo abdominal CT to evaluate for the presence of metastatic infection of the liver, spleen, or kidney; psoas abscess; or other intra-abdominal source. This patient has aortic valve endocarditis, persistent S. aureus bacteremia and fever, new right upper quadrant pain, and abnormal liver chemistry tests, which are concerning for development of liver abscess. Metastatic infections are not uncommon with S. aureus bacteremia and require a careful history and physical examination to identify where to look and what tests to perform next. New right upper quadrant pain with liver chemistry test abnormalities should prompt investigation with imaging studies such as CT, which can also evaluate the spleen, kidney, and pararenal structures that may be seeded during bacteremia. Transesophageal echocardiography (TEE) will also need to be performed because of this patient's fever and persistent bacteremia. Development of a perivalvular abscess is a possibility, especially if conduction abnormalities are present on the electrocardiogram. Compared with transthoracic echocardiography, perivalvular abscesses are better visualized with TEE.

Several neurologic complications can arise from S. aureus endocarditis, including brain abscess, stroke, and meningitis. Neurologic symptoms can be the presenting signs in S. aureus endocarditis (for example, a patient presenting with stroke who has a heart murmur and unexplained fever should be evaluated for endocarditis). New neurologic symptoms that develop during the course of treatment for endocarditis should always be evaluated (such as with head CT). This patient has no neurologic symptoms, so a head CT is not indicated.

Daptomycin is rarely used to treat methicillin-sensitive S. aureus (MSSA) infections except in patients with multiple antibiotic allergies that preclude the use of β-lactams or glycopeptides. Persistent bacteremia is likely a failure of source control and requires careful investigation for possible sources of metastatic infection and drainage if amenable.

Cefazolin is more rapidly bactericidal than vancomycin and is preferred over vancomycin for treatment of MSSA. Therefore, switching would be inappropriate.

Key Point

  • Staphylococcus aureus bacteremia persisting more than 72 hours after the start of appropriate antimicrobial therapy suggests a complicated infection requiring additional evaluation; endocarditis, osteomyelitis, and intra-abdominal infections are important sites of metastatic infection.

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Case 5

Correct answer: D. Switch piperacillin-tazobactam to meropenem.

Antibiotic therapy should be switched from piperacillin-tazobactam to meropenem. This patient has a complicated urinary tract infection (UTI), defined by the presence of a chronic indwelling urinary catheter. The pattern of antibiotic susceptibility of Escherichia coli from the urine culture suggests an extended-spectrum β-lactamase (ESBL)–producing organism. ESBL-producing gram-negative organisms are capable of hydrolyzing higher generation cephalosporins that have an oxyimino side chain, including cefotaxime, ceftazidime, ceftriaxone, and cefepime. Laboratory identification of ESBLs is difficult because they are a heterogeneous group of enzymes. The carbapenem class of antibiotics (imipenem, meropenem, doripenem, ertapenem) is the preferred class of agents for treating infections with ESBL-producing organisms.

Adding gentamicin would provide no benefit. Additionally, this patient has kidney disease; thus, aminoglycosides should be avoided if at all possible.

On laboratory testing, ESBL-producing gram-negative organisms may appear susceptible to piperacillin-tazobactam; however, susceptibility breakpoints do not always reflect clinical success. Thus, piperacillin-tazobactam may be insufficient to treat infections with ESBL-producing organisms. An exception is uncomplicated UTI, in which piperacillin-tazobactam may be effective because high concentrations of the antibiotic are achievable in urine.

The oxyimino cephalosporins (such as cefepime) should not be used, even if an ESBL-producing organism appears to be susceptible on laboratory testing. Treatment failures are common, even with higher doses, so carbapenems are the preferred antibiotic.

Key Point

  • The carbapenem class of antibiotics (imipenem, meropenem, doripenem, ertapenem) is the preferred class of agents for treating infections with extended-spectrum β-lactamase–producing organisms.

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Case 6

Correct answer: A. Cystoscopy and biopsy.

The indication for antimicrobial therapy in this patient is an invasive urologic procedure. Because urine is a sterile body fluid, the presence of significant bacteriuria is considered to be an infection. In men, either 105 cfu/mL of bacteria from voided urine or at least 102 cfu/mL of a single bacterial species from a clean intermittent catheterized sample is required to distinguish true bacteriuria from contamination. Asymptomatic bacteriuria (ASB) is diagnosed when no signs or symptoms of active infection referable to the urinary tract are present. Depending on variables such as age and genitourinary abnormalities, older adult men have an ASB prevalence of approximately 5% to 20% in the community, rising to 15% to 40% in long-term care facilities. It is important to recognize that screening for and possibly treating asymptomatic bacteriuria is supported by only two indications: pregnancy and risk mitigation before an invasive urologic procedure. The use of prophylactic antibiotics before minor noninvasive urologic interventions without mucosal bleeding does not provide any benefit and is not recommended.

Likewise, screening for and treating ASB in patients about to undergo orthopedic surgery, including total joint arthroplasty, is without proven merit because it is not a cause of postoperative surgical site infection.

Data are insufficient to advocate the routine treatment of ASB in kidney transplant recipients or patients with diabetes.

Key Point

  • Screening for and possibly treating asymptomatic bacteriuria is supported by only two indications: pregnancy and medical clearance before an invasive urologic procedure.