This population based survey is the first to integrate household level data and molecular epidemiology and finds significant and independent relationships linking community, health-related and hygiene exposures with serious skin infection at both the individual and the household level. This finding was not replicated in analyses that examined the relationship between these same exposures and S. aureus nasal colonization. However, the nasal colonization data did provide evidence of intra-household S. aureus transmission. The objective of this exploratory research was to determine if S. aureus colonization is a useful proxy measure to study disease transmission and infection in community settings; the results suggest that colonization is an incomplete proxy variable. In addition, the study also highlights the importance of the household unit as a significant community reservoir, since more than 40% of households were colonized and one quarter had household members with serious recent skin infections.
While increases have been observed in the community in both the prevalence and incidence of S. aureus
infection, parallel increases in the incidence and prevalence of nasal colonization have not uniformly been observed 
, even among high risk populations 
. Rather, S. aureus
nasal colonization has been stable across both time and populations. Therefore, while S. aureus
nasal colonization is an important marker of potential subsequent infection among hospital populations, it may not fully reflect S. aureus
exposure and risk in the community, though it clearly plays a role. Ultimately however, S. aureus
nasal colonization alone may not be a satisfactory proxy measure in the community setting 
Little is understood about the exact mechanisms of S. aureus
transmission within the community, beyond a generic conceptual idea that transmission occurs through ‘contact.’ Research examining infectious disease transmission dynamics using social network methods has found that the prevalence of infection and the degree of contact infected individuals have with other group members, plays a significant role in both disease prevalence and incidence within a community 
. This research began with the most ubiquitous and easily identified network in the community setting: the household, where more than 40% were found to be colonized. While it is not surprising that a higher percentage of households than individuals are colonized, the magnitude of colonization (>40%) suggests that households are an underappreciated and substantial community reservoir for infection.
As early as 1960, Roodyn 
understood the importance of the household but observed “… that even in the comparative simplicity of the single household, the epidemiology of staphylococcal infections appears baffling.” This is the first study to address the household network on a large scale. These data found that more than two in every five households were colonized. Moreover, one fifth of multiperson households had multiple members colonized, half of whom were colonized with the same strain, suggesting at least some degree of intra-household transmission. Yet the data from this study suggest that the factors contributing to S. aureus
infection are manifold and extend beyond the household.
The lack of strain similarity suggests that many strains are resident in the community and are regularly introduced into the household. These strains may then be transmitted either within the household or to extra-household contacts. Sexual transmission, both homosexual 
and heterosexual 
, is a novel mechanism that is increasingly well documented and that may effectively spread pathogens. In addition, risk factors that introduce S. aureus
into the household (e.g.
, international travel, sports participation or recent surgery), are the same mechanisms through which individuals living in colonized households may re-introduce the pathogens to the community.
The role played by antibiotic use is deserving of special attention, since approximately one quarter of the more than 900 study participants had used antibiotics in the past six months, which translated to antibiotic usage by more than half of all randomly selected households. While antibiotic use independently conferred protection from S. aureus
colonization among households, it was also independently associated with increased serious skin infections at both the individual and the household level. The data suggest that at least some usage may be unmonitored, given the high levels of self-reported non-prescription antibiotic use. Uncontrolled and perhaps inappropriate use of antibiotics has the potential to eventually increase resistance not only to methicillin, but to other first and second line antibiotics as well, allowing these increasingly antibiotic-resistant strains to circulate in the community. This phenomenon is already being observed 
Studies have documented considerable variation in the prevalence of methicillin-resistant S. aureus
(MRSA) infections in different geographic regions 
. While this study identified primarily susceptible S. aureus
strains, there is no evidence to date to suggest that MRSA strains such as USA300, while perhaps more efficiently transmitted, are spread via different modalities. The presence or absence of the mec
element does not appear to influence transmissibility 
. The results from this randomly selected household sample suggest that the low background prevalence of MRSA is the sole limiting factor in large-scale colonization, since there is little to differentiate those colonized by S. aureus
from those colonized by MRSA, or for that matter, those not colonized at all. Therefore, it is essential to identify mechanisms of transmission and other community reservoirs, in order to develop and implement interventions prior to a widespread dissemination of MRSA.
This study has limitations. The study population was largely Hispanic and therefore may not necessarily apply to other populations. Much of the data are self-reported and may underreport individual practices. There is evidence that underreporting occurred for socially undesirable factors (e.g.
, illicit drug use). Although egocentric network data collection, whereby one person provides data for a group of individuals, is standard in social network research, individuals may underreport network member risk factors because of lack of knowledge. Underreporting would bias findings to the null. We cannot be certain that all skin infections were due to S. aureus
or that the respondents recalled infections of the other household members although the bulk of skin infections are due to S. aureus 
. In addition, RDD has been criticized for potential sample undercoverage due to the exclusion of cell-phone-only households. Only the nares were cultured; sampling of other body sites would likely have yielded a higher number of colonized participants 
. Alternatively prior antibiotic use may also have affected the rates of colonization in our sample. While some studies have documented limited nasopharyngeal penetration of many antibiotics, it remains possible that colonization was affected by the recent use of antibiotics 
. Finally, despite the large number of individuals represented in this study, the household sample size was small. Larger community samples, as well as the inclusion of a more diverse sample, and innovative methodologies will be required to address current study limitations.
The multidisciplinary approach utilized in this study, combining epidemiology, social network methods and microbiology, facilitated an exploration of two separate lines of inquiry addressing S. aureus transmission within the community. The first line of inquiry identified significant relationships between several community, health-related and hygiene exposures and serious skin infection, but not S. aureus colonization. Results from the second line of inquiry suggest that households represent a significant S. aureus community reservoir, since more than 40% of households were colonized and 25% reported serious skin infection. The lack of association between S. aureus nasal colonization and serious skin infection underscores the need to explore alternative venues, environmental or body sites that may be crucial to transmission, as well as the importance of carrying out community based research independent of healthcare settings, in order to better understand S. aureus transmission dynamics in the community and to develop effective prevention strategies.