1 in 20 patients may have MRSA

The largest and most comprehensive study to date of the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in U.S. healthcare facilities indicates that 46 out of every 1,000 patients were either infected or colonized with the bacteria—a rate as much as 11 times greater than previous estimates.

The Association for Professionals in Infection and Epidemiology (APIC) conducted the survey of 1,237 facilities in October and November of 2006. The respondents, which were located in all 50 states, represented approximately 21 percent of all U.S. healthcare facilities and 28 percent of the average daily census. Healthcare facilities ranged in size from 8 beds to 1,668 licensed beds (with an average of 256 beds). They included acute care, rehabilitative care, and long-term care facilities; women’s and children’s hospitals; and Veterans Affairs (VA) facilities. The institutions reported a total of 187,058 inpatients during the survey period.

Survey results
The following statistics represent the major results of the survey:

• Total number of patients with MRSA colonization/infection: 8,654
• Overall MRSA rate (infection and colonization): 46.3 per 1,000 inpatients
• Clinical culture-positive MRSA rate: 34 per 1,000 inpatients (range: 16 to 48 per 1,000 inpatients)
• Percentage of infections detected by clinical cultures: 81
• Percentage of infections detected by active surveillance cultures: 19
• Percentage of infections detected within 48 hours of admission: 77
• Percentage of infections detected more than 48 hours after admission: 23
• Percentage of infected patients with skin and soft-tissue infections only: 37
• Percentage of infected patients with infections at other sites: 63
• Percentage of isolates susceptible to clindamycin: less than 30
• Percentage of isolates susceptible to levofloxacin: less than 20

The MRSA rate of 46.3 per 1,000 inpatients is between 8 and 11 times greater than previous estimates, which were based on incidence rather than prevalence data. If only clinical culture results are counted (ignoring MRSA colonization data), the MRSA rate of 34 per 1,000 inpatients is still more than eight times greater than the recent estimate of 3.95 MRSA infections per 1,000 discharges by Kuehnert and associates. (Kuehnert MJ, Hill HA, Kupronis BA, Tokars JI, Solomon SL, Jernigan DB. Methicillin-resistant-Staphylococcus aureus hospitalizations, United States. Emerg Infect Dis 2005;11:868-872.)

Concerns about MRSA have been increasing since it emerged as a source of nosocomial infections more than 30 years ago. Today, it is the most common cause of hospital-acquired infections and has spread to facilities around the world. It is estimated to account for between 50 percent and 70 percent of the S aureus infections acquired in healthcare facilities and is an emerging community pathogen.

Community-acquired MRSA (CA-MRSA) usually causes skin and soft-tissue infections, as opposed to hospital-acquired MRSA (HA-MRSA), which causes bloodstream, surgical site, and urinary tract infections. The MRSA death rate has been estimated to be more than 2.5 times higher than S aureus infections that respond to methicillin.

About APIC
The survey was funded by APIC’s Research Foundation and conducted by William R. Jarvis, MD, president and cofounder of Jason and Jarvis Associates, a private consulting firm in healthcare epidemiology. Previously, Dr. Jarvis spent 23 years at the U.S. Centers for Disease Control and Prevention (CDC) in Atlanta, Ga, where he held a number of supervisory positions in epidemiology, research, and infectious diseases.

APIC has conducted numerous surveys of healthcare professionals as part of its mission to improve health and patient safety by reducing risks of infection and other adverse outcomes. The Washington, D.C.-based association has more than 10,000 members, who have primary responsibility for infection prevention, control, and hospital epidemiology in healthcare settings around the globe. Members include nurses, epidemiologists, physicians, microbiologists, clinical pathologists, laboratory technologists, and public health practitioners. APIC was established in 1973 in response to the need for an organized, systematic approach to the “control” of infections acquired as a result of hospitalization.

Additional details of the survey, its methodology, and its results may be accessed at http://www.apic.org/MRSAstudy.

Jason Calhoun, MD, is past chair of the Infections Committee and currently serves on the Patient Safety Committee. He may be reached at calhounj@health.missouri.edu.