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Community MRSA rising in HIV/AIDS patients
Is immune deficiency the key?
Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections are becoming more prevalent in certain populations, particularly the HIV infected and intravenous drug users, researchers are finding. As CA-MRSA strains like USA300 afflict these groups, they become more entrenched in communities and pose the risk of hospital transmission on subsequent admissions. Indeed, some hospitals are reporting that community MRSA has virtually displaced the long established nosocomial strains.
"This is definitely an emerging phenomenon with community-acquired MRSA," says Tony Trinh, MD, an internal medicine resident at the Warren Alpert Medical School of Brown University and Rhode Island Hospital in Providence, RI.1 "It's emerging in the general population and in the HIV population. It's an alarming trend because these strains are very hardy, and they obviously tend to go in circles and groups of people who are at high risk."
For example, research is showing a statistical association between HIV and CA-MRSA among an HIV population investigators studied in Chicago, IL, says Kyle Popovich, MD, an infectious diseases physician at the Rush University Medical Center in Chicago.2
CA-MRSA infections have emerged nationally among children, athletes, prisoners, and military personnel, with close proximity and shared items often cited as among the likely reasons.
"Now we're seeing community-acquired MRSA even among people who are not part of these populations, so it's spreading," Popovich says. "[Still], the recent growth of CA-MRSA cases has been higher among HIV-positive individuals than among HIV-negative individuals in the population we examined."
Popovich and co-investigators reviewed cases and found that HIV patients with CA-MRSA and skin and soft-tissue infections were often seen in outpatient clinics and emergency rooms. "Studies have shown that skin and soft-tissue infections in some ERs are very common," she says.
Among the HIV patients that were hospitalized with CA-MRSA skin and soft-tissue infection, the study population was predominantly African American and male. More than 80% were black, and 72% were men, and the mean age was around 40 years. Other common characteristics included a history of illicit drug use among 61% and men who have sex with men (MSM) among 22%. "We looked at people who were hospitalized, and we looked at intensive care unit admission," Popovich says. "We focused on skin and soft tissue infections, but didn't look at bloodstream infections."
A retrospective review of 900 HIV-infected outpatients from January, 2002, to December, 2007, showed that 8% were colonized or infected with MRSA.3 The researchers concluded that HIV-infected patients at significant risk for MRSA were those who had a CD4 cell count of less than 200 cells and who had antibiotic exposure. In contrast, patients who had been on antiretroviral for the previous year had a significantly reduced risk of MRSA colonization.
Though Trinh's study did not find a relationship between AIDS-defining illness and CA-MRSA infection, he says there is definitely an immune deficiency related aspect to why HIV patients are presenting with these soft-tissue infections. "It's not wholeheartedly explained by immune deficiencies that come with HIV, but these are alluding to possible processes that are not well-defined yet," he adds.