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MRSA prevalence varies widely across US
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MRSA rates varied significantly among academic medical centers in California, Illinois, New York and North Carolina, according to study results published in Clinical Infectious Diseases.
In most cases, methicillin-susceptible Staphylococcus aureus (MSSA) rates moved in opposite directions of MRSA rates, suggesting that infection control and prevention efforts were not responsible for the variations in community-onset cases of infection.
“These dramatic differences in the incidence and rate of change in the number of MRSA and MSSA infections indicate ongoing, fundamental changes in bacterial ecology, which need further study to protect public health,” study researcher Brad Spellberg, MD, an infectious disease specialist at Los Angeles Biomedical Research Institute, said in a press release. “Fully understanding MRSA, MSSA and other antibiotic-resistant infections is essential to finding new approaches to save the lives and protect the health of our patients here and around the world.”
Brad Spellberg
Spellberg and colleagues reviewed hospital records to determine the number of community-onset (CO) MRSA and MSSA cases recorded each year from 2008 and 2011 at five medical centers in Chicago, Los Angeles, New York City, Raleigh-Durham, N.C., and San Francisco. They identified 4,171 episodes of bacteremia, of which 42.9% were MRSA infections and 57.1% were MSSA infections.
Overall, the incidence of CO-MRSA increased 33%, from 0.3 to 0.4 per 1,000 patient-days (P<.001) during the study period, whereas the incidence of CO-MSSA bacteremia declined from 0.52 to 0.45 per 1,000 patient-days (P<.001). The discordant rates of infection were driven by changes in the ecology and epidemiology of MRSA, according to the researchers.
The researchers observed significant variations in bacteremia rates across all five centers. CO-MRSA rates declined significantly in Los Angeles, from 0.42 per 1,000 patient-days in 2009 to 0.18 per 1,000 patient-days in 2011 (P=.005). At the same time, rates of CO-MRSA remained stable at the San Francisco and Raleigh-Durham medical centers. In contrast, CO-MRSA rates more than tripled at the New York hospital, from 0.11 to 0.34 cases per 1,000 patient-days (P<.001).
The incidence of CO-MSSA did not change significantly except in New York, where rates declined from 0.53 to 0.39 per 1,000 patient-days (P<.001).
The researchers also examined the incidence of hospital-onset bacteremia and found lower rates of infection at each center compared with community-onset cases, indicating “that efforts to prevent MRSA infections should be focused on outpatient settings as well as inpatient settings,” they wrote.
Results also indicated that the USA300 strain accounted for 52% of genotyped MRSA isolates, but varied at each center, from 35% to 80%.
Spellberg and colleagues said Chicago and Los Angeles were among the first geographical areas affected by the emergence of CO-MRSA infections during the 1990s, whereas New York has only recently been affected by the epidemic. This has led them to believe that the stable CO-MRSA rates observed in Chicago and the declining rates of infection identified in Los Angeles will soon be seen on the East Coast.
Disclosure: See the study for a full list of the researchers’ financial disclosures.
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