MRSA Infection Control and Prevention - Academic Year
2026/2027 - Final Comprehensive Examination Questions -
119 Questions with Answers
Page 1
,Q1. A hospital epidemiologist notes a rising prevalence of MRSA strains with reduced
vancomycin susceptibility (MIC = 2 µg/mL). Which molecular mechanism is most
directly associated with this phenotype?
A. Acquisition of the vanA gene cluster from enterococci
B. Mutations in the vraSR two-component regulatory system leading to cell wall
thickening
C. Overexpression of the mecA gene encoding PBP2a
D. Production of the Panton-Valentine leukocidin toxin
Correct Answer: B. Mutations in the vraSR two-component regulatory system
leading to cell wall thickening
Rationale: Reduced vancomycin susceptibility in MRSA (hVISA/VISA) is primarily due to
mutations in the vraSR and graSR regulatory systems that cause cell wall thickening and
trapping of vancomycin. The vanA gene cluster is characteristic of vancomycin-resistant
enterococci and is rare in MRSA. mecA overexpression confers beta-lactam resistance, not
vancomycin resistance. PVL is a virulence factor, not associated with vancomycin
susceptibility.
Why Wrong:
A - The vanA gene cluster is typically found in VRE and is extremely rare in MRSA.
C - mecA overexpression only affects beta-lactam resistance, not vancomycin.
D - PVL is a toxin that enhances virulence, not involved in vancomycin resistance.
Reference: Howden BP, et al. Reduced vancomycin susceptibility in Staphylococcus
aureus, including vancomycin-intermediate and heterogeneous strains:
resistance mechanisms, laboratory detection, and clinical implications. Clin
Microbiol Rev. 2010.
Q2. In a neonatal intensive care unit, routine surveillance cultures identify multiple
infants colonized with MRSA. Whole-genome sequencing reveals a common clone.
Which infection control intervention is most critical to prevent ongoing transmission?
A. Contact precautions for colonized infants and enhanced environmental cleaning
B. Decolonization of all infants with mupirocin and chlorhexidine baths
C. Restricting visitor access to the unit
D. Antibiotic prophylaxis for all infants
Correct Answer: A. Contact precautions for colonized infants and enhanced
environmental cleaning
Rationale: When a common clone is identified, transmission is likely ongoing. The most
critical intervention is to implement contact precautions for colonized infants and enhance
environmental cleaning to break the chain of transmission. Decolonization may be
considered but is not the primary intervention in an outbreak and may not be appropriate
for all infants. Restricting visitors and antibiotic prophylaxis are not evidence-based and
can be harmful.
Page 2
,Why Wrong:
B - Decolonization is not universally recommended in neonates due to safety concerns
and is not the first-line outbreak control measure.
C - Visitor restriction has limited impact on healthcare-associated transmission.
D - Antibiotic prophylaxis is not indicated and increases resistance risk.
Reference: Siegel JD, et al. Management of multidrug-resistant organisms in healthcare
settings, 2006. CDC/HICPAC.
Q3. A researcher is evaluating a novel rapid molecular assay for MRSA detection
directly from blood cultures. The assay targets the mecA gene and the S.
aureus-specific spa gene. Which limitation is most important to consider?
A. The assay cannot distinguish between MRSA and methicillin-resistant
coagulase-negative staphylococci
B. The assay may produce false-negative results for mecA-positive, mecA-negative
MRSA (mecC)
C. The assay does not provide antimicrobial susceptibility data for non-beta-lactam
antibiotics
D. The assay requires a minimum of 24 hours to produce results
Correct Answer: C. The assay does not provide antimicrobial susceptibility data for
non-beta-lactam antibiotics
Rationale: Molecular assays that detect mecA and spa genes provide rapid identification
of MRSA but do not yield phenotypic susceptibility data for other antibiotics like
vancomycin or linezolid. While they may miss mecC variants, that is not the primary
limitation in routine clinical use. The assay is specific for S. aureus, so it won't detect
coagulase-negative staph. Results are typically available in a few hours, not 24.
Why Wrong:
A - The presence of the spa gene ensures specificity for S. aureus, not
coagulase-negative staphylococci.
B - mecC is rare and not the primary limitation; the assay is designed to detect mecA.
D - Rapid molecular assays typically provide results in under 5 hours, not 24.
Reference: Buchan BW, et al. Comparison of the BD MAX MRSA assay and the Cepheid
Xpert MRSA assay for the detection of methicillin-resistant Staphylococcus
aureus in nasal swabs. J Clin Microbiol. 2015.
Q4. A hospital is updating its environmental cleaning protocols to reduce MRSA
transmission. Which strategy has the strongest evidence for reducing MRSA
contamination on high-touch surfaces?
A. Daily cleaning with quaternary ammonium compounds
B. Use of ultraviolet-C (UV-C) light disinfection after terminal cleaning
Page 3
, C. Increased frequency of cleaning with detergent only
D. Application of copper-impregnated surfaces in patient rooms
Correct Answer: B. Use of ultraviolet-C (UV-C) light disinfection after terminal
cleaning
Rationale: UV-C light disinfection has been shown in multiple studies to reduce MRSA
contamination on surfaces when used as an adjunct to terminal cleaning. Quaternary
ammonium compounds are effective but not superior to other EPA-registered disinfectants.
Detergent-only cleaning is less effective. Copper-impregnated surfaces reduce
contamination but are not a cleaning strategy and require installation.
Why Wrong:
A - Quaternary ammoniums are standard but not the strongest evidence-based strategy
compared to UV-C.
C - Detergent-only cleaning is less effective at removing MRSA.
D - Copper surfaces are a passive intervention, not a cleaning protocol.
Reference: Weber DJ, et al. Effectiveness of ultraviolet devices and hydrogen peroxide
systems for terminal room decontamination: Focus on clinical trials. Am J
Infect Control. 2016.
Q5. A patient develops a severe MRSA bloodstream infection. The isolate is
susceptible to vancomycin (MIC 1 µg/mL) but resistant to oxacillin. Which treatment
strategy is most appropriate according to current guidelines?
A. Vancomycin monotherapy with therapeutic drug monitoring
B. Daptomycin 6 mg/kg IV once daily
C. Linezolid 600 mg IV every 12 hours
D. Cefazolin 2 g IV every 8 hours
Correct Answer: A. Vancomycin monotherapy with therapeutic drug monitoring
Rationale: For MRSA bacteremia, vancomycin remains a first-line agent if the MIC is "d2
µg/mL, with careful monitoring of trough levels. Daptomycin is an alternative but requires
higher doses (8-10 mg/kg) and is not first-line. Linezolid is not preferred for bacteremia
due to its bacteriostatic nature and limited outcomes data. Cefazolin is ineffective against
MRSA.
Why Wrong:
B - Daptomycin is a second-line option and requires higher dosing; not the most
appropriate first-line.
C - Linezolid is bacteriostatic and not the preferred agent for bacteremia.
D - Cefazolin is a beta-lactam and ineffective against MRSA.
Reference: Liu C, et al. Clinical practice guidelines by the Infectious Diseases Society of
America for the treatment of methicillin-resistant Staphylococcus aureus
infections in adults and children. Clin Infect Dis. 2011.
Page 4
2026/2027 - Final Comprehensive Examination Questions -
119 Questions with Answers
Page 1
,Q1. A hospital epidemiologist notes a rising prevalence of MRSA strains with reduced
vancomycin susceptibility (MIC = 2 µg/mL). Which molecular mechanism is most
directly associated with this phenotype?
A. Acquisition of the vanA gene cluster from enterococci
B. Mutations in the vraSR two-component regulatory system leading to cell wall
thickening
C. Overexpression of the mecA gene encoding PBP2a
D. Production of the Panton-Valentine leukocidin toxin
Correct Answer: B. Mutations in the vraSR two-component regulatory system
leading to cell wall thickening
Rationale: Reduced vancomycin susceptibility in MRSA (hVISA/VISA) is primarily due to
mutations in the vraSR and graSR regulatory systems that cause cell wall thickening and
trapping of vancomycin. The vanA gene cluster is characteristic of vancomycin-resistant
enterococci and is rare in MRSA. mecA overexpression confers beta-lactam resistance, not
vancomycin resistance. PVL is a virulence factor, not associated with vancomycin
susceptibility.
Why Wrong:
A - The vanA gene cluster is typically found in VRE and is extremely rare in MRSA.
C - mecA overexpression only affects beta-lactam resistance, not vancomycin.
D - PVL is a toxin that enhances virulence, not involved in vancomycin resistance.
Reference: Howden BP, et al. Reduced vancomycin susceptibility in Staphylococcus
aureus, including vancomycin-intermediate and heterogeneous strains:
resistance mechanisms, laboratory detection, and clinical implications. Clin
Microbiol Rev. 2010.
Q2. In a neonatal intensive care unit, routine surveillance cultures identify multiple
infants colonized with MRSA. Whole-genome sequencing reveals a common clone.
Which infection control intervention is most critical to prevent ongoing transmission?
A. Contact precautions for colonized infants and enhanced environmental cleaning
B. Decolonization of all infants with mupirocin and chlorhexidine baths
C. Restricting visitor access to the unit
D. Antibiotic prophylaxis for all infants
Correct Answer: A. Contact precautions for colonized infants and enhanced
environmental cleaning
Rationale: When a common clone is identified, transmission is likely ongoing. The most
critical intervention is to implement contact precautions for colonized infants and enhance
environmental cleaning to break the chain of transmission. Decolonization may be
considered but is not the primary intervention in an outbreak and may not be appropriate
for all infants. Restricting visitors and antibiotic prophylaxis are not evidence-based and
can be harmful.
Page 2
,Why Wrong:
B - Decolonization is not universally recommended in neonates due to safety concerns
and is not the first-line outbreak control measure.
C - Visitor restriction has limited impact on healthcare-associated transmission.
D - Antibiotic prophylaxis is not indicated and increases resistance risk.
Reference: Siegel JD, et al. Management of multidrug-resistant organisms in healthcare
settings, 2006. CDC/HICPAC.
Q3. A researcher is evaluating a novel rapid molecular assay for MRSA detection
directly from blood cultures. The assay targets the mecA gene and the S.
aureus-specific spa gene. Which limitation is most important to consider?
A. The assay cannot distinguish between MRSA and methicillin-resistant
coagulase-negative staphylococci
B. The assay may produce false-negative results for mecA-positive, mecA-negative
MRSA (mecC)
C. The assay does not provide antimicrobial susceptibility data for non-beta-lactam
antibiotics
D. The assay requires a minimum of 24 hours to produce results
Correct Answer: C. The assay does not provide antimicrobial susceptibility data for
non-beta-lactam antibiotics
Rationale: Molecular assays that detect mecA and spa genes provide rapid identification
of MRSA but do not yield phenotypic susceptibility data for other antibiotics like
vancomycin or linezolid. While they may miss mecC variants, that is not the primary
limitation in routine clinical use. The assay is specific for S. aureus, so it won't detect
coagulase-negative staph. Results are typically available in a few hours, not 24.
Why Wrong:
A - The presence of the spa gene ensures specificity for S. aureus, not
coagulase-negative staphylococci.
B - mecC is rare and not the primary limitation; the assay is designed to detect mecA.
D - Rapid molecular assays typically provide results in under 5 hours, not 24.
Reference: Buchan BW, et al. Comparison of the BD MAX MRSA assay and the Cepheid
Xpert MRSA assay for the detection of methicillin-resistant Staphylococcus
aureus in nasal swabs. J Clin Microbiol. 2015.
Q4. A hospital is updating its environmental cleaning protocols to reduce MRSA
transmission. Which strategy has the strongest evidence for reducing MRSA
contamination on high-touch surfaces?
A. Daily cleaning with quaternary ammonium compounds
B. Use of ultraviolet-C (UV-C) light disinfection after terminal cleaning
Page 3
, C. Increased frequency of cleaning with detergent only
D. Application of copper-impregnated surfaces in patient rooms
Correct Answer: B. Use of ultraviolet-C (UV-C) light disinfection after terminal
cleaning
Rationale: UV-C light disinfection has been shown in multiple studies to reduce MRSA
contamination on surfaces when used as an adjunct to terminal cleaning. Quaternary
ammonium compounds are effective but not superior to other EPA-registered disinfectants.
Detergent-only cleaning is less effective. Copper-impregnated surfaces reduce
contamination but are not a cleaning strategy and require installation.
Why Wrong:
A - Quaternary ammoniums are standard but not the strongest evidence-based strategy
compared to UV-C.
C - Detergent-only cleaning is less effective at removing MRSA.
D - Copper surfaces are a passive intervention, not a cleaning protocol.
Reference: Weber DJ, et al. Effectiveness of ultraviolet devices and hydrogen peroxide
systems for terminal room decontamination: Focus on clinical trials. Am J
Infect Control. 2016.
Q5. A patient develops a severe MRSA bloodstream infection. The isolate is
susceptible to vancomycin (MIC 1 µg/mL) but resistant to oxacillin. Which treatment
strategy is most appropriate according to current guidelines?
A. Vancomycin monotherapy with therapeutic drug monitoring
B. Daptomycin 6 mg/kg IV once daily
C. Linezolid 600 mg IV every 12 hours
D. Cefazolin 2 g IV every 8 hours
Correct Answer: A. Vancomycin monotherapy with therapeutic drug monitoring
Rationale: For MRSA bacteremia, vancomycin remains a first-line agent if the MIC is "d2
µg/mL, with careful monitoring of trough levels. Daptomycin is an alternative but requires
higher doses (8-10 mg/kg) and is not first-line. Linezolid is not preferred for bacteremia
due to its bacteriostatic nature and limited outcomes data. Cefazolin is ineffective against
MRSA.
Why Wrong:
B - Daptomycin is a second-line option and requires higher dosing; not the most
appropriate first-line.
C - Linezolid is bacteriostatic and not the preferred agent for bacteremia.
D - Cefazolin is a beta-lactam and ineffective against MRSA.
Reference: Liu C, et al. Clinical practice guidelines by the Infectious Diseases Society of
America for the treatment of methicillin-resistant Staphylococcus aureus
infections in adults and children. Clin Infect Dis. 2011.
Page 4
