Heterosexual Transmission of CA-MRSA

March 1, 2007

National report - Sexual transmission of community-acquired MRSA (CA-MRSA) may be an important and underappreciated part of the recent upsurge in infections across the country.

The first documentation of heterosexual transmission of CA-MRSA came from a recent longitudinal study conducted in upper Manhattan.

"We thought we knew what to expect; this was a surprise to us," says Heather A. Cook, M.P.H., a community health researcher at the Columbia University College of Physicians and Surgeons. She is lead author of the paper that appeared in the Feb. 1 issue of Clinical Infectious Diseases.

The survey found less than 1 percent colonization in those nasal samples, which is consistent with national studies. However, local reports of CA-MRSA incidence were higher, prompting Ms. Cook and her colleagues to speculate that perhaps colonization and carriage was occurring elsewhere on the body.

Why sexual transmission may be difficult to uncover

Ms. Cook tells Dermatology Times that part of the difficulty in pinpointing this type of transmission is the taboo surrounding sexual issues.

"Patients will readily show a lesion on an arm, but hesitate to show one in the pubic area," she says.

Other factors

Other factors contributing to an underappreciation of the prevalence of CA-MRSA are limited access to healthcare, physician misdiagnosis, and the fact that carriage does not necessarily lead to an active infection in the host, but can result in transmission and active infection in others.

The paper lays out three case studies of sexual transmission within family households. In most instances, the nasal passages tested negative for carriage, while the pubic area was positive. One risk factor researchers identified as associated with colonization is microabrasions of the skin from shaving or another infection.

"Women get diagnosed and treated, but their husbands or partners do not, and they end up getting reinfected. It's pingponging back and forth," Ms. Cook says.

As with every sexually transmitted infection, it is important to get the partner involved and treated.

All of the infections were with the USA300 strain of CA-MRSA. It is unclear whether there is something about that particular strain of the bacteria that prefers the tissue and environmental niche of the pubic area to the nasal passages.

The study included a few men who have sex with men, but those index cases did not live with a sexual partner and so the team did not pursue them.

Ms. Cook suggests that, at a minimum, the nose, armpits and pubic area be sampled when trying to determine colonization with CA-MRSA. She emphasizes the need to treat the partner as well as the patient, and to make sure that patients complete the course of antibiotics. Failure to do so contributes to potential reinfection.

Doctor not surprised

Gregory J. Moran, M.D., clinical professor of emergency medicine at the University of California, Los Angeles, has a special interest in MRSA.

"It's always hard to sort out transmission that is specifically due to sexual contact and what is due to physical contact of any type, whether it is sexual or not," he says.