Background: A hospitalised patient infected with MRSA was found to
harbour a VISA strain after 6 weeks of treatment with vancomycin.
Additional contact measures were reinforced according to CDCs
recommendations. We decide to evaluate if these applied control
measures were effective.
Objective: To evaluate the efficacy of strict additional contact measures
to contain the dissemination of VISA from an infected patient.
Methods: All patients from the unit were screened weekly for MRSA
during a 6-week period, whereas health care workers (HCW) were
screened only once. Screening specimen included nose, throat, groin,
and clinical specimens for patients, and only nose and throat for
HCW. Broth enrichment and chromogenic agar (MRSA-select) were
used for MRSA detection. All MRSA isolates were tested on Van
screen plates, and growing colonies were tested for MIC of vancomycin.
MIC was performed using Etest. Population analysis was done for
VISA confirmation. One strain per person was typed by Double Locus
Sequence Typing (based on clfB and spa sequencing).
Results: 66 patients hospitalized in the same service during the 6 weeks
and 55 HCW were screened for MRSA and VISA. MRSA was found in
16/66 (24%) patients and 1/55 (2%) HCW. 16/17 MRSA from patients
belonged to the same genotype that the VISA strain. The remaining
patient had a MRSA identical to the HCW isolate.
Among the 16 MRSA isolates sharing the same genotype than the VISA
strain, two showed Etests vancomycin MIC of only 4 mg/L. MIC results
were confirmed by the population analysis. They were not considered
as VISA, but as MRSA with increased vancomycin MICs. Both isolates
were obtained from two roommates.
Conclusion: Strict additional contact measures were found to be
effective to contain VISA dissemination. However, the identification of
two isolates with increased vancomycin MIC (4 mg/L) in two roommates
raised the question of the need to routinely test this susceptibility and of
adequate control measures for patients harbouring such isolates.