Friday, September 22, 2023
Isolate and Patient Characteristics for 300 Veterans who had Staphylococcus aureus bacteremia
at 4 Veterans Affairs Medical Centers, USA, 2004–2008*
Infection Characteristics for 300 Veterans who had Staphylococcus aureus Bacteremia
at 4 Veterans Affairs Medical Centers, USA, 2004–2008
Patient and Infection Characteristics for 300 Veterans with Staphylococcus aureus Bacteremia
and Association with Illicit Drug Use at 4 Veterans Affairs Medical Centers, USA, 2004–2008*
Patient and Infection Characteristics for 300 Veterans with Staphylococcus aureus Bacteremia
and Association with USA300 MRSA at 4 Veterans Affairs Medical Centers, USA, 2004–2008*
Independent Risk Factors for USA300 MRSA Bacteremia
Among 300 Veterans at 4 Veterans Affairs Medical Centers, USA, 2004–2008*
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We identified 300 patients with S. aureus bacteremia at the 4 participating sites during the study period. Strains having all 3 genetic factors (PVL, ACME, and spa type motif MBQBLO) were classified as USA300 MRSA, and a random sample of these isolates showed 100% sensitivity and specificity by PFGE. Isolates with none of these genetic factors were classified as non-USA300 MRSA, and a random sample of these isolates also showed 100% sensitivity and specificity by PFGE. Isolates with 1 or 2 of the genetic factors were also designated as non-USA300 MRSA; 18% of these isolates were found to be USA300 MRSA by PFGE, resulting in 100% sensitivity and 82% specificity of the laboratory algorithm for identifying USA300 MRSA. Sixty-seven (22%) of the infections were caused by USA300 MRSA, 117 (39%) by non-USA300 MRSA, and 116 (39%) by MSSA.
Patient and infection characteristics of the study population are presented in Table 1 and Table 2 . Of all patients with S. aureus bacteremia, 22 (7%) were illicit drug users, 13 (59%) with injection drugs. The patients had a mean age of 68 years and were almost all male (98%). Infections were classified as nosocomial in 172 (57%) patients, 83 (48%) of which were central-line associated. Sixteen (5%) patients were infected with HIV and 80 (27%) had a previous episode of colonization or infection with MRSA.
Compared with patients who did not use illicit drugs, illicit drug users were younger (mean age 51 vs. 69; p<0.0001; Table 3 ) and more likely to be African American (17% vs. 3%; p<0.0001). Illicit drug users were more likely to have HIV (38% vs. 6%; p<0.0001) or endocarditis (16% vs. 6%; p = 0.04) and less likely to have acquired their infection nosocomially (3% vs. 13%; p = 0.003) than patients who did not use illicit drugs. Illicit drug users were significantly more likely to have a bacteremic infection caused by USA300 MRSA than by all other S. aureus strains, compared with patients who did not use illicit drugs (RR 3.04, 95% confidence interval [CI] 1.99-4.64; p<0.0001; Table 4 ). Age (mean age 63 vs. 69 years; p = 0.0004) and a nosocomial acquisition of infection (RR 0.44, 95% CI 0.29-0.69; p = 0.0002) were both negatively associated with USA300 MRSA bacteremia.
Using binomial regression, illicit drug users were significantly more likely to have USA300 MRSA bacteremia compared with patients not using illicit drugs, controlling for year of presentation (adjusted RR [aRR] 3.00, 95% CI 1.88-4.36; p<0.0001; Table 5 ). This result was due to an increase in the proportion of S. aureus bacteremic infections caused by the USA300 MRSA strain in patients who did not use illicit drugs over the study period, while the proportion in patients using illicit drugs remained relatively stable after 2004. Stratified by year of presentation (categorized as early [January 1, 2004-March 31, 2006] vs. late [April 1, 2006-June 30, 2008] years of presentation), the association of illicit drug use with USA300 MRSA bacteremia decreased over the study period (RR in early years of presentation 4.63, 95% CI 2.36-9.07; p<0.0001; RR for late years of presentation 2.45, 96% CI 1.38-4.35; p = 0.02). The association of illicit drug use and USA300 MRSA bacteremia weakened over the study period, although the trend was not statistically significant (p = 0.23 for trend over time; Figure).
;)
EnlargeAssociation Between Illicit Drug Use and USA300 Methicillinresistant Staphylococcus aureus Bacteremia among 300 Veterans at 4 Veterans Affairs Medical Centers, USA, 2004–2008 (generalized linear model p value for trend over time = 0.23). †No illicit drug users had a bacteremic infection caused by USA300 MRSA in 2006.
