SAN DIEGO The incidence of health care-associated invasive methicillin-resistant Staphylococcus aureus infections in the United States fell 12.5% between 2005 and 2007, a decline that was statistically significant.
The decline was even greater among patients with hospital-onset bloodstream MRSA infections, according to preliminary results from a study of data from the Active Bacterial Core (ABC) surveillance program. The ABC is a component of the Emerging Infections Program Network, a collaboration between the Centers for Disease Control and Prevention (CDC), state health departments, and universities.
Although the results are encouraging, they are preliminary and require further prospective analysis, lead investigator Dr. Alexander J. Kallen cautioned at the annual meeting of the Society for Healthcare Epidemiology of America.
"The 2007 data set has not been finalized, and although only a small number of additional reports are expected, this may result in some changes in these estimates," said Dr. Kallen, a medical officer with the CDC's Division of Healthcare Quality Promotion in Atlanta.
The ABC surveillance program began tracking MRSA infections in 2004 and includes a catchment area of about 15 million people at facilities in nine statesCalifornia, Colorado, Connecticut, Georgia, Maryland, Minnesota, New York, Oregon, and Tennessee.
Dr. Kallen and his associates evaluated only MRSA-causing, invasive health care-associated infectionsdefined as MRSA isolated from a normally sterile sitein a resident of the surveillance area from 2005 to 2007. This included hospital-onset isolates, defined as isolates cultured more than 2 calendar days after admission when the day of admission is day 0, and health care-associated community-onset isolates, which were cultured 2 days or less after admission in patients with a recent health care exposure. Health care exposures included presence of a central venous catheter at the time of admission, a history of dialysis, an overnight stay in a health care facility, or surgery within the previous year.
To determine population-based incidence by year, the researchers used a denominator based on United States census estimates for the catchment area.
In another component of the study, clinicians at eight of the nine facilities were asked to complete a 42-question survey about MRSA-related infection control practices. Nearly 90% of isolates were from a bloodstream infection; the next most common syndrome was pneumonia or empyema, followed by skin and soft tissue infection, Dr. Kallen reported.
Between 2005 and 2007, the overall incidence of all invasive MRSA infections fell 12.5%, from 42.7 per 100,000 patients to 34.4 per 100,000 patients, which was statistically significant.
When the researchers studied the subset of patients with bloodstream infections, defined as a positive blood culture, they observed a 21% decrease in hospital-onset infections between 2005 and 2007 and a 12% decrease in health care-associated community-acquired infections during the same time period. Both reductions were statistically significant.
Meanwhile, incidence of MRSA bloodstream infections in dialysis patients fell 7% in the time period, a reduction that did not reach statistical significance.
According to the survey portion of the study, nearly 70% of responding facilities performed some type of active surveillance testing. More than 80% of facilities used contact precautions for MRSA patients, used dedicated equipment for MRSA patients, could detect previously MRSA-colonized or infected patients at admission, and maintained at least simple measures of MRSA incidence or prevalence.
Limitations of the study include the fact that ABC "is a population-based surveillance system and that use of the catchment area population as a denominator for this analysis of health care-associated infections may be suboptimal," Dr. Kallen said.
He went on to emphasize that he and his associates "cannot determine the precise cause for this fall in MRSA incidence from our data. This is one cross-sectional study. However, health care facilities we polled had implemented a large number of MRSA-control interventions."
Dr. Kallen had no financial conflicts to disclose.
The overall incidence of all invasive MRSA infections dropped by a statistically significant 12.5%. DR. KALLEN
Nearly 90% of MRSAisolates were from a bloodstream infection; the next most common was pneumonia or empyema, followed by skin and soft tissue infection. Courtesy Dr. Derek Jones