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Prevalence of MRSA at admission predicted acquisition rate
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An analysis of 112 Veterans Affairs Medical Centers found that admission prevalence of methicillin-resistant Staphylococcus aureus was predictive of the disease’s acquisition rate, and vice versa.
“Nosocomial MRSA infections decreased because MRSA transmission decreased,” Makoto Jones, MD, MS, research investigator and staff physician at the George E. Wahlen Department of Veterans Affairs Medical Center in Salt Lake City, told Infectious Disease News. “The prevention of one patient MRSA acquisition starts a cascade of prevented acquisitions among that patient’s contacts, and then the contact’s contacts and so on.”
Makoto Jones
Jones and colleagues analyzed the admission prevalence of MRSA, the acquisition rates of MRSA and the incident nosocomial clinical culture (INCC) rates, which are surrogates for importation, transmission and nosocomial infection, respectively. They included data from all patients in acute care from Oct. 1, 2007, to Sept. 30, 2010.
During this time, there were 2.9 million surveillance tests taken from 1.4 million admissions and 742,531 individuals. At hospital admission, the mean prevalence of MRSA was 11.4%. The acquisition rate was 5.2 per 1,000 patient-days at risk and the INCC rate was 1.8 per 1,000 patient-days at risk.
When the hospital’s average admission prevalence increased by 10%, the weekly acquisition rate and INCC rate increased by 9.7% and 9.8%, respectively.
“We did not see an obvious decrease in nosocomial MRSA infections among patients who were known MRSA carriers on admission,” Jones said. “More study is needed, but this would suggest that we could improve on infection control measures that target progression from silent carriage to symptomatic disease.”
Jones also said that although MRSA infections appear to be decreasing, other investigations have suggested that vancomycin use has not. They are investigating ways to encourage providers to use vancomycin more judiciously. They are interested in developing advanced statistical models that are guided by transmission dynamic theory, to develop measures of infection control quality and to study the dynamics of MRSA carriage and the influence of antibiotics on MRSA transmission. These methods could potentially be expanded to other pathogens, such as carbapenem-resistant Enterobacteriaceae.
Disclosure: This study was supported by the Department of Veterans Affairs, Veterans Health Administration, Health Services Research and Development Service through the Informatics, Decision Enhancement and Surveillance Center, the Consortium for Healthcare Informatics Research; the Veterans Informatics and Computing Infrastructure, and the CDC Epicenter, with resources and facilities at the VA Salt Lake City Health Care System.
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