Low colonization prevalence of Staphylococcus aureus with reduced vancomycin susceptibility among patients undergoing hemodialysis in the San Francisco Bay area.
BACKGROUND
Staphylococcus aureus exhibits varying degrees of reduced vancomycin susceptibility, and strains with intermediate levels of resistance are thought to emerge by antibiotic selection of subpopulations in heterogeneously resistant precursor strains exposed to this antibiotic. We sought to determine the prevalence of and risk factors for carriage of potential heterogeneous vancomycin-intermediate S. aureus (hVISA).


METHODS
We prospectively observed a cohort of 211 patients undergoing hemodialysis and performed quarterly surveillance cultures for up to 2 years. We screened for reduced vancomycin susceptibility using brain-heart infusion agar with 4 microg/mL vancomycin.


RESULTS
We identified 10 colonizing potential hVISA isolates recovered from 7 patients among both methicillin-susceptible and methicillin-resistant S. aureus strains. No confirmed hVISA isolates were identified; we can be 95% certain that the prevalence of confirmed hVISA carriage does not exceed 1.4%. When compared with noncolonized hemodialysis patients, neither vancomycin exposure, duration of hospitalization, nor any baseline clinical or demographic factor was found to predict colonization with potential hVISA on univariate analyses; increased number of months receiving hemodialysis was associated with potential hVISA colonization on multivariate analysis.


CONCLUSIONS
Despite numerous published reports of S. aureus with reduced vancomycin susceptibility, carriage of these isolates remains a rare phenomenon. Given the unclear clinical significance of potential hVISA, it is not clear whether clinical laboratories should identify such strains, or how they should do so.
Eguia
Jose M
JM
Division of Infectious Diseases, San Francisco General Hospital, University of California, San Francisco, CA 94143-0811, USA. jeguia@itsa.ucsf.edu
Liu
Catherine
C
Moore
Matthew
M
Wrone
Elizabeth M
EM
Pont
Joan
J
Gerberding
Julie L
JL
Chambers
Henry F
HF
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002353:Carrier State / Q000382:microbiology*; D015331:Cohort Studies; D024881:Drug Resistance, Bacterial; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009666:Nose / Q000382:microbiology; D015995:Prevalence; D011446:Prospective Studies; D006435:Renal Dialysis; D012307:Risk Factors; D012495:San Francisco / Q000453:epidemiology; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification / Q000502:physiology; D014640:Vancomycin / Q000494:pharmacology*
D014640:Vancomycin