Determination of the prevalence and incidence, molecular characterization, and nasal and pharyngeal colonization patterns of Staphylococcus aureus among urban and rural Iowans

Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA) has been characterized in swine workers and other high-risk groups in the United States, but little is known about non-high risk groups. We intend to determine the prevalence of S. aureus and MRSA colonization in Iowans at baseline, observe incident colonization events during follow-up, and determine the frequency of transmission within family units. We will also assess the oropharynx as a distinct colonization site within our population of healthy community members.

A prospective, longitudinal cohort study was conducted, enrolling 263 individuals, comprising 95 family units, from Johnson County and Keokuk County. Participants self-collected swabs weekly, with adults providing nasal and oropharyngeal samples and minors providing nasal samples. S. aureus isolates were confirmed with catalase and coagulase tests, and StaphLatex agglutination assays. Molecular characteristics were determined through mecA and PVL polymerase chain reaction, and spa typing. Demographic and risk factor data were collected via self-report questionnaire at baseline.

Of the 263 enrolled individuals, 78 adults (9 with MRSA) and 31 minors (1 with MRSA) were positive for S. aureus at baseline. This gives an overall S. aureus prevalence of 44.1% and 36.1% for adults and children respectively, with 5.1% and 1.2% of these isolates being MRSA respectively. Sensitivity for the nares was 57.7% while sensitivity for the oropharynx was 85.9%. Of adults submitting 14 or more sets of swabs, 13 (8.44%) were colonized in the oropharynx greater than 50% of samples while being colonized in the nares less than 50% of samples, indicating preferential oropharynx colonization. Risk factors identified for preferential oropharynx colonization were the number of positive environmental sites within the participant's home, size of the household, and race of the participant. Transmission events were observed for both adults and minors, with 3.95 events observed per participant year of follow-up for adults and 3.04 events per person year of follow-up for minors. Familial transmission events were observed at a rate of 0.77 events per person year of follow-up for adults, and 1.22 events per person year of follow-up for minors.

We hypothesized oropharyngeal colonization would be important in healthy community members. This hypothesis is supported by the greater sensitivity observed at baseline when compared to the nares. The identification of 13 preferential oropharynx carriers also supports the hypothesis. Utilizing the results from this dissertation, our findings of the importance of environmental contamination in colonization of both the oropharynx and the nares support the use of environmental decontamination to prevent familial transmission of S. aureus. The results of this study confirm the oropharynx as a distinct and unique colonization site for S. aureus, but further studies are needed to determine the clinical ramifications.