Staphylococcus aureus Colonization Among Household Contacts of Patients With Skin Infections: Risk Factors, Strain Discordance, and Complex Ecology

The emergence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections in the late 1990s [1] has resulted in a dramatic shift in the epidemiology of S. aureus infections. In the United States, the predominant CA-MRSA clone, USA300 MRSA, has become the most common cause of community-associated skin infection [2] and an endemic pathogen in many hospitals [3–5]. Data suggest that CA-MRSA infections have high attack rates in household contacts after an initial CA-MRSA infection occurs [6, 7]. In contrast to healthcare-associated (HA)–MRSA strain types, which have circulated in the healthcare setting for more than 40 years and rarely spread outside the hospital [8–10], there is evidence that CA-MRSA strain types frequently spread from person to person in households [11–14]. Although transmission of HA-MRSA may occur in part via asymptomatic carriers [8], less is known about MRSA and methicillin-susceptible S. aureus (MSSA) dissemination in community settings. Previous investigations of MRSA spread in households have been limited by relatively small sample size [15–21], lack of geographic diversity [16, 19–22], focus on HA-MRSA [23, 24], nares-only surveillance [17, 19, 20, 22, 25, 26], or lack of distinction among S. aureus genetic backgrounds at the molecular level [23]. Recent investigations suggest nares-only screening may underestimate S. aureus colonization prevalence because S. aureus has been found to colonize oropharyngeal [27–29] and inguinal areas [30–32] in persons irrespective of nasal colonization. Additionally, although USA300 MRSA is the most common genetic background causing CA–S. aureus skin infection [2], MRSA nasal colonization remains uncommon in the general population (<5%) [33]. To better understand the spread of USA300 MRSA and other S. aureus strain types in households, we studied S. aureus colonization in patients with skin infections and among their household members in 2 large US cities.