Trends in Superbug Screening Identify Most Likely Carriers of Deadly Bacteria in Hospital Settings

Findings released last week from a new study at the American Society for Microbiology's 46th Annual Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC) provide doctors with a more complete epidemiologic picture of high-risk groups most likely to carry deadly organisms. Presumed carriers of superbugs, (multidrug resistant bacteria) responsible for causing a growing number of U.S. hospital acquired infections (HAIs), were identified through a universal surveillance program encompassing more than 90 percent of admitted patients over 12 months.

Conducted by Evanston Northwestern Healthcare in Evanston, Ill., the study, Prevalence of Colonization with Methicillin-Resistant Staphylococcus aureus (MRSA) Among 24,045 Patients Screened at an Acute Care Hospital, sampled patients at least once from August 01, 2005 until July 31 of 2006. Results show how health care organizations can better target patients colonized with MRSA. Significant predictors of MRSA colonization include: being male; older age; living in a nursing home or assisted living facility, and hospital admission within the prior two years.

Rapid results of new molecular diagnostics enabled the universal surveillance of over 20,000 patients screened for MRSA upon admittance to the hospital, said Dr. Lance Peterson, director of microbiology and infectious disease research at Evanston Northwestern Healthcare and one of the authors of the study. This hard data confirms some suspicions and helps those working in the infection control field to better hone our screening recommendations and definition of those patients at highest-risk of carrying MRSA.

According to the Centers for Disease Control and Prevention (CDC), HAIs cause 90,000 deaths per year in the United States and can cause an estimated eight million excess hospital days and more than $5 billion in excess healthcare costs, with MRSA being the leading microbe of all HAIs. Lurking on the body of one in every 20 patients entering the hospital is one of the most troublesome bacteria, MRSA.(1)  Past research has shown that of those patients who have it on their bodies at admission, up to one in five develops an infection.(2) 

For patients who acquire MRSA while in the hospital, up to 25 percent develop a potentially lethal infection (3) and in the United States alone MRSA accounts for nearly 60 percent of the Staphylococcus aureus infections in intensive care units.(4)

In the Evanston Northwestern Healthcare study, 1,309 patients (5.4 percent) were found to carry MRSA. Most importantly, there was a trend of demographic variables identified that might help healthcare institutions to develop a profile of those at highest risk of MRSA colonization.

The data showed that colonization was most prevalent at extremes of age, reaching 19 percent among those aged 90 and older (1,443 patients) and that at least 21 percent of all MRSA-positive patients listed a multi-resident facility as their home address. Also of statistical significance was the fact that colonization was more prevalent in patients with an admission in the prior two years. Evanston Northwestern Healthcare used the BD GeneOhm MRSA assay to conduct all of this research and for their ongoing universal screening program.

Universal surveillance is the most thorough way to identify patients who are carriers of MRSA upon admission, said Dr. Ari Robicsek, the associate epidemiologist at Evanston Northwestern Healthcare who presented this work. But when it isnt feasible, this study suggests that risk factors can be identified by an organization to direct targeted active surveillance.

Additional data from Evanston Northwestern Healthcare released at ICAAC indicate that universal surveillance upon admission is the ideal method of identifying and isolating all carriers of MRSA. However targeted surveillance of high-risk admissions, though less robust, can also be a cost-effective alternative to identify carriers. An additional study to be released tomorrow will compare universal surveillance with targeted active surveillance and passive surveillance.


1. Hidron, Alice l et al, CID 2005; 41: 167-9.

2. Davis, K.A. et al, CID 2004; 39: 776-82.

3. Davis, K.A. et al, CID 2004; 39: 776-82.

4. The Lancet Infectious Diseases, October 2005, page 653; National Nosocomial Infections Surveillance (NNIS) System Report, data summary from January 1992 through June 2004, issued October 2004. Am J Infect Control2004; 32: 470-85 (quoted in The Lancet Infectious Diseases, October 2005, page 653.

Source: Evanston Northwestern Healthcare