843. Molecular Epidemiology of Community-Associated Staphylococcus aureus in Households of Patients with Skin and Soft Tissue Infections
Session: Oral Abstract Session: MRSA - Epidemiological Trends
Saturday, October 22, 2011: 8:30 AM
Room: 157ABC

Endogenous colonization has historically been considered a risk factor for Staphylococcus aureus (SA) infection.  However, the dynamics of acquiring symptomatic infection with contemporary community-associated SA are undefined.  We employed molecular typing to compare colonizing and disease-causing strains of SA within individuals and households.


In a study of 100 pediatric patients (cases) with community-onset SA skin and soft tissue infections (SSTI) and colonization, wound isolates were obtained from cases along with nasal, axillary and inguinal colonization swabs from cases and their household (HH) contacts (n=362).  Repetitive sequence-based PCR was performed to evaluate relatedness (> 95% similar band pattern) of infecting and colonizing strains from each case.  The infecting strains from each case were also compared with SA strains colonizing their HH contacts.


Among 801 SA isolates, 26 distinct strain types were identified.  The number of colonizing and infecting strains per household ranged from 1 to 6 (Table).  Cases carried up to 3 different strains, and 82 cases had at least one HH member colonized. Of 362 HH members, 52% were colonized with SA and 9% carried multiple strains.

Seventy-four cases were colonized in ≥ 1 body site with their infecting strain; of these, 42 (57%) had at least one HH member whose colonizing strain matched the case’s infecting strain. Of the 26 cases whose infecting strain did not match any of their colonizing strains, 9 (35%) had at least one HH member whose colonizing strain matched the case’s infecting strain. 


Almost three quarters of cases were colonized with the strain causing their SSTI.  Over half of cases had a HH member whose colonizing strain matched their infecting strain. Of cases whose SSTI strain did not match their colonizing strain, only one third matched a HH member colonizing strain, suggesting acquisition from source external to the household.  There was a diversity of strains within households.

Table. Number of S. aureus Strains within Households

Number of Distinct Strains

Index Case Baseline


Households Baseline

N= 100

Household Members

N=362 (%)




173 (48)




155 (43)




34 (9)


















Subject Category: C. Clinical studies of bacterial infections and antibacterials including sexually transmitted diseases and mycobacterial infections (surveys, epidemiology, and clinical trials)

Marcela Rodriguez, MD1, Patrick G. Hogan, MPH1, Carey-Ann Burnham, PhD2 and Stephanie A. Fritz, MD1, (1)Pediatric Infectious Diseases, Washington University School of Medicine, St Louis, MO, (2)Pediatrics, Pathology and Immunology, Washington University School of Medicine, St Louis, MO


M. Rodriguez, None

P. G. Hogan, None

C. A. Burnham, None

S. A. Fritz, None

Findings in the abstracts are embargoed until 12:01 a.m. EST Thursday, Oct. 20 with the exception of research findings presented at IDSA press conferences.