According to a recent report published in the August issue of Infection Control and Hospital Epidemiology, infections caused by methicillin-resistant Staphylococcus aureus (MRSA) doubled at academic medical centers nationwide in five years.
University of Chicago Medicine and University HealthSystem Consortium (UHC) researchers estimated that hospital admissions for MRSA infections increased from about 21 out of every 1,000 patients hospitalized in 2003 to about 42 out of every 1,000 in 2008, or almost 1 in 20 inpatients.
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The new findings counter a recent Centers for Disease Control and Prevention (CDC) study that found MRSA cases in hospitals were declining. The CDC study looked only at cases of invasive MRSA, which are infections found in the blood, spinal fluid or deep tissue. It excluded infections of the skin, which the UHC study includes.
“The rapid increase means that the number of people hospitalized with recorded MRSA infections exceeded the number hospitalized with AIDS and influenza combined in each of the last three years of the survey: 2006, 2007 and 2008,” said Michael David, assistant professor of medicine at the University of Chicago and one of the study’s authors, in a press release.
According to David, researchers attribute much of the overall increase they detected to community-associated infections, which are those that were contracted outside the healthcare setting. When MRSA first emerged it was primarily contracted in hospitals or nursing homes.
“Community-associated MRSA infections, first described in 1998, have increased in prevalence greatly in the U.S. in the last decade,” David said in the statement. “Meanwhile, healthcare-associated strains have generally been declining.”
The study utilized the UHC database, which includes data from 90 percent of all not-for-profit academic medical centers in the U.S. However, like many such databases, the UHC data are based on billing codes hospitals submit to insurance companies, which often underestimate MRSA cases.
For example, hospitals might not report MRSA cases that do not affect insurance reimbursement for that particular patient. In other cases, hospitals might be limited in the number of billing codes they can submit for each patient, which can result in a MRSA code being left off the billing report if it was not among the primary diagnoses.
The UHC research team corrected for these errors by using detailed patient observations from the University of Chicago Medical Center and three other hospitals. They looked at patient records to find the actual number of MRSA cases in each hospital over a three-year period. The team then checked the insurance billing data to see how many of those cases were actually recorded. They found that the billing data missed one-third to one-half of actual MRSA cases at the four hospitals. They used that rate of error as a proxy to correct the billing data from the other 420 hospitals in the UHC database and arrive at the final estimates.