Staphylococcus aureus, a common human pathogen, usually resides in nasal passages. In healthy individuals the bacterium is usually harmless but when passed among patients in hospitals or other institutions it can cause a variety of infections. Both community- and hospital-acquired methicillin-resistant strains of S aureus (MRSAs) are on the rise. The authors surveyed children and adults to determine population-based estimates of carriage rates of S aureus and MRSA, using 2001-2002 data from the National Health and Nutrition Survey (NHANES). NHANES is a nationally representative sample of noninstitutionalized people in the U.S. To date, most studies on MRSA have focused on routes of individual transmissions rather than population-level transmissions. To help characterize the disease reservoir, variables such as age, sex, race/ethnicity, birth place, poverty-income ratio, self-reported health status, past hospitalizations and use of antibiotics were identified.

Key Findings

• An average of 32.4 percent of the U.S. population carries S aureus.
• Hispanics had a higher rate of S aureus than did other ethnic groups, as did women generally.
• 2.58 percent (0.84% of the total population) of carriers had MSRA, equalling 2.2 million people.
• Young people carrying S aureus are unlikely to carry MRSA; older people are less likely to carry S aureus, but are more likely to have MRSA.

The authors suggest that older people with S aureus infections may need initial treatment with antibiotics that cover resistant strains. They also urge continued monitoring of populations, as carriage rates can change quickly. Because of the small sample size of the MRSA-positive group, the study was unable to further characterize this group.