Methicillin-resistant staphylococcal colonization and infection in a long-term care facility.
OBJECTIVE
To determine the natural history of colonization by methicillin-resistant Staphylococcus aureus (MRSA) among patients in a long-term care facility. We specifically sought to determine if MRSA colonization was predictive of subsequent infection.


METHODS
Cohort study.


METHODS
Long-term Veterans Affairs Medical Center.


METHODS
A total of 197 patients residing on two units were followed with regular surveillance cultures of the anterior nares.


METHODS
The development of staphylococcal infection.


RESULTS
Thirty-two patients were persistent carriers of MRSA and 44 were persistent carriers of methicillin-susceptible strains (MSSA). Twenty-five percent of MRSA carriers had an episode of staphylococcal infection compared with 4% of MSSA carriers and 4.5% of non-carriers (P less than 0.01; relative risk 3.8; 95% CI, 2.0 to 6.4). The rate of development of infection among MRSA carriers was 15% for every 100 days of carriage. Using logistic regression analysis, persistent MRSA carriage was the most significant predictor of infection (P less than 0.001; odds ratio, 3.7). Seventy-three percent of all MRSA infections occurred among MRSA carriers. Isolates of MRSA from 7 patients were typed. Colonizing and infecting strains had the same phage type in all 7 patients and the same pattern of plasmid EcoRI restriction endonuclease fragments in 5 patients.


CONCLUSIONS
Colonization of the anterior nares by MRSA predicts the development of staphylococcal infection in long-term care patients; most infections arise from endogenously carried strains. Colonization by MRSA indicates a significantly greater risk for infection than does colonization by MSSA. The results offer a theoretic rationale for reduction in MRSA infections by interventions aimed at eliminating the carrier state.
Muder
R R
RR
Pittsburgh Veterans Affairs Medical Center, Pennsylvania.
Brennen
C
C
Wagener
M M
MM
Vickers
R M
RM
Rihs
J D
JD
Hancock
G A
GA
Yee
Y C
YC
Miller
J M
JM
Yu
V L
VL
D000368:Aged; D000369:Aged, 80 and over; D001434:Bacteriophage Typing; D002353:Carrier State / Q000453:epidemiology* / Q000382:microbiology; D003428:Cross Infection / Q000453:epidemiology* / Q000382:microbiology; D006801:Humans; D016106:Methicillin Resistance; D008875:Middle Aged; D009666:Nose / Q000382:microbiology; D009735:Nursing Homes; D010957:Plasmids; D011446:Prospective Studies; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology; D013211:Staphylococcus aureus / Q000145:classification* / Q000187:drug effects / Q000302:isolation & purification