USA300 MRSA may be sexually transmitted in MSM

Male–male sex should be considered a risk factor for multidrug-resistant USA300 MRSA infection, independent of previous infection.

Issue: February 2008

Multidrug-resistant USA300 methicillin-resistant Staphylococcus aureus may be significantly more prevalent in men who have sex with men, compared with the general population, according to the results of a recent study. The researchers hypothesized that multidrug-resistant USA300 MRSA may be sexually transmitted in this population.

The researchers conducted a population-based survey in nine hospitals in San Francisco and a cross-sectional study in two outpatient clinics in San Francisco and Boston. The researchers reviewed patients’ data to determine annual incidence, spatial clustering and risk factors for multidrug-resistant USA300 MRSA.

The results showed that the overall incidence of multidrug-resistant USA300 MRSA infection in San Francisco was 26 cases per 100,000 people. Further analysis demonstrated that incidence rates were higher in ZIP codes with a higher percentage of male same-sex couples.

The researchers determined that male–male sex should be considered a risk factor for multidrug-resistant USA300 MRSA infection, independent of previous MRSA infection. This risk also appeared to be independent of HIV status.

Study limitations

The researchers stressed that there are several limitations to the study: it only examined the multidrug-resistant USA300 strain of MRSA and did not assess patients’ sexual behavior risks.

“Our study examined the rate of infection with multidrug-resistant USA300 MRSA, which is only a subset of the usual USA300 MRSA that is susceptible to multiple antibiotics,” Christopher Graber, MD, MPH, one of the study’s researchers and member of the infectious diseases section at the VA Greater Los Angeles Healthcare System, told Infectious Disease News. “We found that this multidrug-resistant clone seemed to be concentrated in the ZIP code corresponding to the Castro district when we examined its prevalence in isolates collected from a population-based study of MRSA in San Francisco in 2004-2005. There had been results of prior studies that described a high frequency of MRSA infection in MSM, so we undertook the clinic-based studies to see if patients self-identifying as MSM were experiencing infections due to this multidrug-resistant USA300 clone more than other populations, which ended up being the case.”

Graber said more information is needed to better understand how multidrug-resistant USA300 MRSA is transmitted and why it may be infecting MSM at an increased frequency. “The retrospective nature of our study did not allow us to systematically investigate how transmission of infection exactly occurred; it only allowed us to identify the presence of multidrug-resistant USA300 MRSA in the MSM population,” Graber said. “We already know that MRSA disease can be spread by close skin-to-skin contact, and we did find that a large number of patients with infection due to multidrug-resistant USA300 MRSA had infections in the buttock/genitoperineal areas; however, we can only make an epidemiologic association and cannot definitively specify a method of transmission.”

Media attention

The study results, which are published in the Feb. 19 issue of Annals of Internal Medicine, were made available on the journal’s website in mid-January.

After its online release, the study received much attention in the mainstream media, including stories garnering headlines cautioning about a “new gay disease” and “the new HIV.” However, experts are concerned that some of this media attention may have misled the general public about the risk for multidrug-resistant USA300 MRSA.

Graber said previous reports and studies have suggested heterosexual transmission of MRSA strains. The mainstream media may be misleading the public into thinking only MSM are at risk for infection with multidrug-resistant USA300 MRSA. “USA300 MRSA is already present in the general population, and it is reasonable to expect that multidrug-resistant USA300 MRSA will spread in the general population as well,” Graber said.

According to Graber, the spread of MRSA strains can be reduced if people maintain proper personal hygiene, including regular bathing and frequent handwashing. “Routine examination of the skin is also important to identify small cuts and abrasions that could serve as points of bacterial entry,” Graber said. “Any person who has an active skin infection should keep draining wounds covered and thoroughly wash or dispose of all material that comes into contact with the wound.”

To reduce the risk for sexual transmission of MRSA strains, people are encouraged to wash with soap and water after sex, particularly if their partners show signs of active skin infection. – Jay Lewis

For more information:

Diep B, Chambers H, Graber C, et al. Emergence of multidrug-resistant, community-associated, methicillin-resistant Staphylococcus aureus clone USA300 in men who have sex with men. Ann Intern Med. http://www.annals.org/cgi/content/full/0000605-200802190-00204v1.