Importance of bacterial burden among methicillin-resistant Staphylococcus aureus carriers in a long-term care facility.
OBJECTIVE
To evaluate the prevalence and transmission of methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization, as well as risk factors associated with MRSA carriage, among residents of a long-term care facility (LTCF).


METHODS
Prospective, longitudinal cohort study.


METHODS
A 100-bed Veterans Administration LTCF.


METHODS
All current and newly admitted residents of the LTCF during an 8-week study period.


METHODS
Nasal swab samples were obtained weekly and cultured on MRSA-selective media, and the cultures were graded for growth on a semiquantitative scale from 0 (no growth) to 6 (heavy growth). Epidemiologic data for the periods before and during the study were collected to assess risk factors for MRSA carriage.


RESULTS
Of 83 LTCF residents, 49 (59%) had 1 or more nasal swab cultures that were positive for MRSA; 34 (41%) were consistently culture-negative (designated "noncarriers"). Of the 49 culture-positive residents, 30 (36% of the total of 83 residents) had all cultures positive for MRSA (designated "persistent carriers"), and 19 (23% of the 83 residents) had at least 1 culture, but not all cultures, positive for MRSA (designated "intermittent carriers"). Multivariate analysis showed that participants with at least 1 nasal swab culture positive for MRSA were likely to have had previous hospitalization (odds ratio, 3.9) or wounds (odds ratio, 8.2). Persistent carriers and intermittent carriers did not differ in epidemiologic characteristics but did differ in mean MRSA growth score (3.7 vs 0.7; P<.001).


CONCLUSIONS
Epidemiologic characteristics differed between noncarriers and subjects with at least 1 nasal swab culture positive for MRSA. However, in this LTCF population, only the degree of bacterial colonization (as reflected by mean MRSA growth score) distinguished persistent carriers from intermittent carriers. Understanding the burden of colonization may be important when determining future surveillance and control strategies.
Stone
Nimalie D
ND
Emory University School of Medicine, Emory University, Atlanta, Georgia, USA. nstone@emory.edu
Lewis
Donna R
DR
Lowery
H K
HK
Darrow
Lyndsey A
LA
Kroll
Catherine M
CM
Gaynes
Robert P
RP
Jernigan
John A
JA
McGowan
John E
JE
Tenover
Fred C
FC
Richards
Chesley L
CL
D002353:Carrier State; D015331:Cohort Studies; D003428:Cross Infection; D006801:Humans; D008134:Long-Term Care; D008137:Longitudinal Studies; D016106:Methicillin Resistance; D009735:Nursing Homes; D015995:Prevalence; D011446:Prospective Studies; D013203:Staphylococcal Infections / Q000453:epidemiology / Q000635:transmission*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification / Q000472:pathogenicity*