Healthcare-Associated Infections and Hospital Microbiology (CLABSI, CAUTI, VAP, Sterilization Monitoring) MCQs

Microbiology · 28 free questions with answers & explanations.

1. A patient in the medical ICU develops fever on day 7 of mechanical ventilation. Quantitative endotracheal aspirate culture grows Pseudomonas aeruginosa at 10⁶ CFU/mL. This meets criteria for ventilator-associated pneumonia (VAP). Which of the following is the MOST important preventive bundle element for VAP in ICU?
2. A central venous catheter (CVC) is placed in the right internal jugular vein. On day 12, blood cultures drawn simultaneously from the CVC and a peripheral vein both grow Staphylococcus epidermidis. CLABSI is suspected. The differential time to positivity (DTP) criterion used to implicate the CVC as the source requires:
3. A patient develops VAP (ventilator-associated pneumonia) on day 8 of mechanical ventilation. BAL quantitative culture grows >104 CFU/mL of Pseudomonas aeruginosa. The primary pathogenesis of VAP involves:
4. A dialysis patient develops Staphylococcus aureus bacteraemia attributed to a tunnelled central line. The minimum duration of antibiotic treatment and the drug of choice (MRSA confirmed) are:
5. A ventilator-associated pneumonia (VAP) is suspected in a patient intubated for 6 days. Quantitative BAL culture is ordered. Which threshold CFU/mL is considered diagnostic for VAP, and what is the advantage of quantitative over semi-quantitative culture?
6. A 60-year-old ICU patient on mechanical ventilation for 8 days develops fever, purulent tracheal secretions, and new infiltrates on CXR. Quantitative BAL culture grows ≥10^4 CFU/mL of Pseudomonas aeruginosa. Which diagnostic criterion and threshold confirms ventilator-associated pneumonia (VAP) using BAL quantitative culture?
7. A hospital infection control team investigates an increase in CLABSI (central line-associated bloodstream infection) rates. Blood cultures drawn through a central venous catheter (CVC) and peripheral vein simultaneously. CVC cultures turn positive at 2 hours, peripheral at 5 hours. What criterion does this differential time to positivity (DTP) satisfy for catheter-related bloodstream infection (CRBSI) diagnosis without removing the line?
8. Biological monitoring of an autoclave (steam sterilizer) is performed using Geobacillus stearothermophilus spore strips. The test is considered PASSED when:
9. A patient in the ICU on mechanical ventilation develops fever with purulent tracheal aspirate on day 5. Quantitative BAL culture grows >10⁵ CFU/mL of Acinetobacter baumannii. The most appropriate empirical therapy for suspected carbapenem-resistant Acinetobacter baumannii (CRAB) VAP, while awaiting final susceptibility, is:
10. Central line-associated bloodstream infection (CLABSI) surveillance criteria require which minimum finding to attribute bacteremia to the central venous catheter?
11. Ventilator-associated pneumonia (VAP) diagnosis in a mechanically ventilated patient requires a clinical pulmonary infection score (CPIS). Which microbiological finding from mini-BAL (bronchoalveolar lavage) is considered diagnostically significant?
12. A patient in the ICU develops fever on day 8 of mechanical ventilation. BAL is performed and quantitative culture grows ≥10^4 CFU/mL of Acinetobacter baumannii. The isolate is resistant to imipenem, meropenem, and colistin. What combination is used for carbapenem-resistant Acinetobacter baumannii (CRAB) with colistin resistance?
13. In monitoring the efficacy of autoclaving (134°C, 3 minutes), which biological indicator organism is used, and what principle does it employ?
14. A patient on mechanical ventilation for 6 days develops new fever, purulent tracheal secretions, new right lower lobe infiltrate on chest X-ray, WBC >12,000/µL. Clinical Pulmonary Infection Score (CPIS) is calculated at 8. According to CDC/NHSN criteria, which sampling method for microbiological diagnosis of VAP has the highest sensitivity without increasing antibiotic-related selection pressure?
15. A urinary catheter-associated UTI (CAUTI) is suspected in a catheterised patient. Urine culture from a freshly collected catheter sample grows E. coli >10^5 CFU/mL with pyuria (>10 WBC/µL). The patient has fever and costovertebral angle tenderness. Which of the following is the most important preventive measure proven to reduce CAUTI rate in ICU settings?
16. The biological indicator used to monitor the efficacy of moist heat (autoclave) sterilization is spores of:
17. A mechanically ventilated ICU patient develops fever on day 5 with new bilateral infiltrates on chest X-ray. BAL is performed and cultures grow 10^5 CFU/mL of Pseudomonas aeruginosa. According to CDC/NHSN criteria, this is classified as:
18. The major modifiable risk factor for catheter-associated urinary tract infection (CAUTI) that is addressed by the 'bladder bundle' intervention is:
19. Central line-associated bloodstream infection (CLABSI) surveillance definition requires a positive blood culture with a pathogen that is not related to another site of infection. For coagulase-negative staphylococci (CoNS), how many positive blood cultures are required to meet NHSN CLABSI criteria?
20. A patient in the medical ICU develops fever on day 5 of central venous catheter placement. Blood cultures drawn from the catheter and peripherally both grow Staphylococcus epidermidis. The catheter blood culture turns positive 2 hours before the peripheral culture. What criterion confirms catheter-related bloodstream infection (CRBSI)?
21. For monitoring the efficacy of an autoclave (steam sterilization), which biological indicator is used, and what is its specific endpoint test?
22. A patient on mechanical ventilation for 7 days develops new fever, purulent tracheal secretions, and a new right lower lobe infiltrate on chest X-ray. Quantitative BAL culture grows Acinetobacter baumannii at 10^5 CFU/mL. What is the diagnostic threshold for BAL confirming ventilator-associated pneumonia (VAP)?
23. A tertiary hospital reports 3 cases of catheter-associated urinary tract infection (CAUTI) in 2 weeks in the same urology ward. All grow Candida tropicalis. What is the CDC definition threshold for CAUTI (as a symptomatic UTI component)?
24. A patient with a central venous catheter develops fever on day 8 of ICU admission. Blood cultures drawn simultaneously from the catheter lumen and a peripheral vein both grow Candida tropicalis. Differential time to positivity (DTTP) shows the catheter bottle flagging positive 2 hours earlier than the peripheral bottle. What does this indicate?
25. Biological monitoring of a steam autoclave uses a Geobacillus stearothermophilus spore strip. A strip processed in a full sterilisation cycle shows growth in the indicator broth after 24 hours at 55°C. What does this indicate?
26. Ventilator-associated pneumonia (VAP) diagnosis requires quantitative culture of broncho-alveolar lavage (BAL). The standard diagnostic threshold for BAL quantitative culture is:
27. A urinary catheter-associated UTI (CAUTI) is diagnosed when a catheterised patient has symptoms AND urine culture grows ≥10³ CFU/mL of a uropathogen. However, asymptomatic bacteriuria (ASB) in a catheterised patient should be treated with antibiotics in which ONE situation?
28. A hospital infection control team is investigating a cluster of Clostridioides difficile infections (CDI). Which disinfectant is MOST effective for environmental decontamination of C. difficile spores on ward surfaces?