Fall in MRSA infection in HIV patients

Rates of community-acquired MRSA (methicillin-resistant Staphylococcus aureus) infections in patients with HIV appear to be declining. A US study conducted between 2002 and 2009, and published in the online edition of AIDS, showed that rates of MRSA increased steadily until 2007, but have fallen sharply since.

Gay and other men who have sex with men (MSM) and injecting drug users (IDU) had a higher risk of MRSA than other patients. A low CD4 cell count and younger age were also risk factors for the infection.

“Our findings reproduce those of other studies that have reported immunodeficiency, MSM, IDU and younger age as independent risk factors for MRSA infections in HIV patients,” comment the investigators.

Taking HIV therapy appeared to reduce the risk of infection with MRSA.

Information on rates of MRSA infections and its risk factors among HIV-positive patients attending the Atlanta Veteran’s Affairs Medical Center were collected between 2002 and 2009.

The study involved individuals receiving inpatient and outpatient care.

A total of 168 individuals were diagnosed with 226 MRSA infections during the study. These patients represented 11% of the entire HIV cohort receiving care at the clinic.

Most (99%) of the patients were men, 84% were black, and their median age was 45. The median CD4 cell count at the time MRSA infection was diagnosed was 325 cells/mm³.

However, 40 infections occurred in individuals with CD4 cell counts below 50 cells/mm³ and a further 46 in patients whose CD4 cell count was between 51 and 200 cells/mm³.

Half the patients were taking antiretroviral therapy at the time of MRSA diagnosis.

Nearly all the infections (94%) were community acquired.

There were 184 skin and soft tissue infections. Most of these affected the extremities (42%) or the anogenital region (32%). Other common sites of infection were the face (12%) and scalp (7%). A quarter of patients experienced a recurrence of their MRSA infection.

Higher rates of MRSA infections were seen in gay and other MSM (3.43 cases per 100 person years) and injecting drug users (3.69 cases per 100 person years) than in individuals from other HIV risk groups (1.51 cases per 100 person years; comparison, p < 0.0001).

Patients with a CD4 cell count below 50 cells/mm³ had a high incidence of MRSA (4.17 cases per 100 person years), and rates of the infection were also high among patients with a CD4 cell count between 51 and 200 cells/mm³ (1.39 cases per 100 person years). However, incidence of the infection was markedly lower for individuals with better-preserved immunity (0.81 cases per 100 person years; comparison p < 0.0001).

Patients under 60 had a markedly higher incidence of MRSA than older individuals (2.85 vs 0.81 per 100 person years; p < 0.004).

Much lower incidence of MRSA was seen in patients who were taking HIV therapy than those who were not (1.81 vs 5.10 cases per 100 person years, p < 0.0001).

“To our knowledge, this study is the first to suggest HAART may result in a reduced risk of MRSA infections,” comment the investigators. They suggest that possible reasons for this finding include control of viral load or better immune status.

Infection rates peaked in 2007 at 5.10 cases per 100 person years, but by 2009 had fallen to a little over 1.5 cases per 100 person years. The investigators note that this fall mirrors the decline in MRSA rates seen in the general population.

“Whether the observed decrease in incidence in parallel with this nationwide downward trend is the result of local changes in infection control practices, or any HIV-specific factors will need to be prospectively studied,” conclude the authors.