SAN FRANCISCO — Invasive methicillin-resistant Staphylococcus aureus was more likely to cause skin and soft tissue disease or joint infections if acquired in the community rather than in a hospital, according to preliminary data from a large surveillance study.
Skin or soft tissue infection occurred in 34% of community-associated methicillin-resistant S. aureus (MRSA), compared with 10% of hospital-associated MRSA in the study of 6,413 cases of invasive MRSA in nine U.S. sites with a population of about 16 million people.
Endocarditis was more common with community-associated MRSA than with hospital-associated MRSA (12% vs. 4%), as were internal or deep-seated abscesses (9% vs. 4%) and septic arthritis, Susan M. Ray, M.D., said at the annual meeting of the Infectious Diseases Society of America.
“These differences may be explained by virulence factors in the staph strain, and/or by delay in presentation for care,” said Dr. Ray of Emory University, Atlanta. “The clinical evaluation of community-associated MRSA should include the investigation of deep-seated foci of infections.”
Patients with hospital-associated invasive MRSA were more likely to have uncomplicated bacteremia.
A previous analysis of 2001–2002 data from the Centers for Disease Control and Prevention reported that about 17% of MRSA cases in three sites were community associated, and about 7% of these were invasive disease (with a culture from a normally sterile site).
The current study analyzed federal data from 2004 and 2005 in nine geographic areas for culture-positive invasive MRSA infections. Surveillance officers reviewed patient records to classify 86% of cases as hospital-associated based on risk-factor criteria; all others were deemed community-associated infections (14%) or uncertain (less than 0.5%).
The rate of community-associated MRSA varied widely by geography, comprising 24% of invasive MRSA cases in Maryland but only 3% of cases in New York.
Compared with hospital-associated invasive MRSA, higher rates of community-associated MRSA were seen in children, smokers, and men with a history of intravenous drug use, HIV, or AIDS. Community-associated MRSA was less likely to be resistant to antimicrobials besides methicillin or to be resistant to multiple classes of antibiotics compared with hospital-associated MRSA.
Community-associated MRSA accounted for 35% of invasive MRSA in children aged 3 years or younger, 50% of cases in 4- to 19-year-olds, 25% of patients aged 20–49 years, and 7% of those aged 50 years or older.
Cases were defined as hospital-associated MRSA if records showed at least one of the following: previous MRSA colonization or infection; a culture obtained more than 48 hours after hospitalization; the presence of an invasive device at the time of evaluation; or a history within the past year of hospitalization, surgery, dialysis, or residence in a long-term care facility.
Investigators in the study began collecting isolates from a sample of cases in 2005. “In the future, this will allow us to compare the epidemiologic classification of community-associated MRSA with its microbiologic characteristics,” Dr. Ray said.