MRSA in HIV-positive patients often community acquired, associated with HIV disease severity

Infection with MRSA, or methicillin-resistant Staphylococcus aureus, is being observed with greater frequency among HIV-positive patients, according to an epidemiological study presented on Friday at the Twelfth Annual Retrovirus Conference in Boston. The study also suggests that the majority of MRSA infections in HIV-positive people are being acquired in the community, rather than in hospital, and that the risk of being diagnosed is increased by more advanced HIV disease.

Clinical illness due to infection with MRSA is becoming an increasingly frequent post-surgical complication throughout the developed world due to antibiotic resistance. However, recent studies have begun to suggest that the bacterial infection is often acquired in the community and can be unrelated to recent medical treatment.

To assess its prevalence in people with HIV, researchers from the University of California set out to evaluate MRSA episodes in a retrospective cohort of patients attending an HIV clinic in San Diego. In total, the investigators analysed the medical records of 3455 patients with 7003 person-years of follow-up.

One hundred and twenty six episodes of MRSA were identified between January 2000 and December 31 2003, of which 94 were judged to be clinically significant. Eighty-three percent of the cases involved skin or soft tissue infection, 10% blood infection, 6% respiratory infection and 1% other infection sites.

Working on the assumption that an episode of MRSA infection within six months of a hospital stay indicated MRSA acquisition in the health care setting (nosocomial), researchers were surprised to discover that 60% of cases appeared to be community acquired. When antibiotic susceptibility was assessed, only co-trimoxazole (Septrin / Bactrim) resistance in the MRSA isolate was significantly associated with nosocomial acquisition.

Another surprising finding was a 6.2-fold increase in MRSA incidence between the first six month period and the last six month period evaluated. People who had acquired HIV through heterosexual intercourse were 90% less likely to be diagnosed with MRSA than other risk groups (p = 0.012), and people with viral load above 100,000 copies/ml were almost twice as likely to be diagnosed with MRSA when compared with people who had viral load below 10,000 copies/ml (p

Having a low CD4 cell count also increased the risk of diagnosis with MRSA: patients with CD4 cell counts below 50 cells/mm³ were 2.5 times more likely to be diagnosed than those with higher cell counts (p = 0.003). Conversely, being on antiretroviral therapy reduced the risk of MRSA by 40% (p = 0.02).

Being African American was not associated with any modified risk of being diagnosed with MRSA. However, no data were presented on the risk of current intravenous drug use on MRSA diagnosis.

Christopher Mathews, presenting, acknowledged that the study’s findings are limited by their analysis of cases from a single clinic. He also conceded that a proportion of the reported increase in MRSA prevalence could be explained by increased vigilance on behalf of doctors following publication of previous reports.

However, the study suggests that community-acquired MRSA may be worrying problem among HIV-positive populations, and that there is a direct effect of HIV disease severity on the risk of being diagnosed with the infection.