IAC: MRSA Risk 18 Times Higher in HIV Patients

TORONTO, Aug. 15 -- HIV patients are 18 times more likely than the general population to become infected with community acquired methicillin-resistant Staphylococcus aureus (MRSA), and the rate appears to be increasing, a U.S. researcher said here.

The implication for clinicians is that any soft-tissue infection in an HIV patient should be treated with suspicion, reported Nancy Crum-Cianflone, M.D., of the Tri-Service AIDS Clinical Consortium in San Diego, at the 16^th International AIDS Conference.

"You should culture it," Dr. Crum-Cianflone said, "and begin using antibiotics empirically against MRSA without waiting for the culture."

Dr. Crum-Cianflone and colleagues conducted a retrospective analysis of community acquired MRSA cases among 425 HIV-positive members of the military treated at the San Diego clinic from 1993 to 2005.

•25 patients (or 5.9%) had developed a community acquired MRSA infection over the study period, but all of the cases occurred after 2002.

•During the years 2003, 2004 and 2005, the rate of infections climbed 17-fold, a rate of increase that was statistically significant at P<0.001.

•The incidence rate in 2005 was 40.4 cases per 1,000 patient-years among the HIV-positive cohort.

•By contrast, the rate among HIV-negative people treated at the same center was 2.3 cases per 1,000 patient-years.

All of the cases involved soft tissue and 16% required hospital care, Dr. Crum-Cianflone said, although no patient developed bacteremia and none died. She added that 16% had recurrent infections, despite appropriate antibiotic care.

The significant risk factors for community acquired MRSA infections, after a multivariate analysis, included recent use of ?-lactam antibiotics, a history of syphilis, and a high viral load. A high CD4 count was protective, Dr. Crum-Cianflone said.

One message for clinicians is to be careful about the use of antibiotics, she said. "Maybe we're overusing antibiotics in this population, because we have to in order to fight opportunistic infections," Dr. Crum-Cianflone said.

In another study presented at the same session, Gregory Kirk, M.D., of Johns Hopkins reported that highly active antiretroviral therapy (HAART) protects against community acquired pneumonia regardless of a patient's immune status.

The study, of the long-running ALIVE cohort in Baltimore, compared the incidence of community acquired pneumonia in HIV-positive and -negative injection drug users. As expected, HIV infection was strongly associated with community acquired pneumonia -- those with the infection were 8.5 times more likely to get the disease than those without, with a 95% confidence interval from 6.5 to 11.1.

A multivariate analysis showed that other factors predicted increased risk, including:

•Cigarette smoking (the odds ratio was 1.9, with a 95% confidence interval from 1.3 to 2.8).

•Recent injection drug use (the odds ratio was 1.5, with a 95% confidence interval from 1.2 to 1.9).

•And being female (the odds ratio was 1.3, with a 95% confidence interval from 1.0 to 1.7).

The last finding remains a puzzle, Dr. Kirk said. "There's no clear evidence of some immune gender difference," he said, so researchers are postulating that women may have some environmental factors that render them more vulnerable. One possibility, he said, is that women may do more child care and thus pick up pathogens from their children.

On the other hand, he said, patients on HAART were half as likely to get community acquired pneumonia, a finding that held true no matter how robust was a patient's immune system. The odds ratio was 0.5, with a 95% confidence interval from 0.26 to 0.94.

The studies are "interesting" but not entirely surprising, commented Wafaa El-Sadr, M.D., of Columbia in New York, because people with HIV are known to be at higher risk of a variety of infections.

In particular, it has been known that people with HIV are at increased risk for MRSA, she said, but "it has not been fully understood what risk factors are involved" so the study by Dr. Crum-Cianflone adds to the available information.