In this study, 444 nose cultures of 2,055 patients from 13 enrollment centers resulted in growth of MRSA. The researchers found that 14 percent and 15 percent of inpatient and outpatient hemodialysis patients, respectively, carried nasal MRSA, as did 16% of HIV infected patients, and 20 percent of long-term elder care residents. Based on these findings, Mermel, who is also a professor of medicine at The Warren Alpert Medical School of Brown University and a physician with University Medicine, recommends, "Hospitals performing active surveillance for MRSA should consider such patient populations for screening cultures."

The researchers also found different strains of MRSA in different patient populations. For example, while USA100 was the most common MRSA strain detected, the USA 300 strain was much more commonly found in HIV-infected patients. The researchers also detected some MRSA strains not previously identified in the US, such as an MRSA clone common in Brazil.

Mermel and his colleagues also found dramatic diversity in the quantity of MRSA colonizing the noses of people. Some people had as few as 3 colonies of MRSA in their nose detected with a nasal swab whereas others had as many as 15 million colonies of MRSA. Mermel notes, "This finding is important because heavy MRSA colonization of the nose is an independent risk factor for the development of a surgical site infection."

Mermel says the study findings identify patient populations at increased risk for MRSA carriage and infection. Future studies can use this information to determine a biologic explanation for differences in strains and quantities of MRSA that some people carry in their noses.

Source: Lifespan