Hospital outpatient settings are grappling with a rate of methicillin-resistant Staphylococcus aureus that has doubled between 1999 and 2006, an increase caused almost entirely by community-acquired bacteria strains, according to a new CDC report.
The rapid rate of infection spread threatens inpatient settings as well, according to the December issue of the Centers for Disease Control and Prevention's Emerging Infectious Diseases, which summarizes findings from 300 microbiology labs serving U.S. hospitals.
"The frequency of community-acquired (CA) MRSA among inpatients increased nearly in conjunction with outpatient rates, overall and at each infection site," according to the report.
"Despite increases in the proportion of CA-MRSA strains among inpatients, the continuing high level of (hospital-acquired) HA-MRSA suggests that in contrast to reports from local institutions, CA-MRSA strains are adding to the problem of MRSA rather than replacing HA-MRSA strains."
The report added that some "crowding out of HA-MRSA strains within the hospital may be occurring." However, hospital-acquired strains may be "more fit, and thus CA-MRSA strains are unable to replace them fully. The result is a coexistence of both strains in the hospital and maintenance of CA-MRSA because of the large influx of colonized and infected patients."
Community-acquired MRSA in outpatient settings is an increasing concern, the report said, because the infections spread to inpatients through hospital staff interaction "or use of similar hospital resources, such as surgical rooms."
The finding is especially worrisome because increasingly, hospital care is shifting from inpatient to outpatient settings, with outpatients outnumbering inpatients 3 to 1. Also, federal payers will no longer reimburse providers for infections they are deemed to have caused.
The report, by Eili Klein, David L. Smith, and Ramanan Laxminarayan, said CA-MRSA "has become a major problem in US hospitals already dealing with high levels" of hospital-acquired staph infections. Klein and Laxminarayan are affiliated with Princeton University. Smith is from the University of Florida at Gainesville, and all three are associated with Resources for the Future, Washington, DC.
Understanding these trends can "help hospital administrators and policy makers make infection control investments to address the role that large influxes of outpatients with CA-MRSA infections may play with regard to overall MRSA infection rates in the hospital."