The rates of hospital- and community-acquired methicillin-resistant Staphylococcus aureus infection of the skin and soft tissue all declined significantly in recent years, according to a report in the July 4 JAMA that analyzed longitudinal trends within the U.S. Department of Defense Military Health System.
The findings of this study, "taken together with results from other [studies] showing decreases in the rates of health-care-associated infections from MRSA, suggest that broad shifts in the epidemiology of S. aureus infections may be occurring," said Dr. Michael L. Landrum of the infectious disease service at San Antonio Military Medical Center, Fort Sam Houston, Texas, and his associates.
They added that, despite these declines, the burden of S. aureus bacteremia and skin and soft-tissue infections still remains "substantial."
The investigators examined the current epidemiology of both MRSA and methicillin-susceptible S. aureus (MSSA) using data from medical beneficiaries treated in 2005-2010 at 266 military health care facilities. Notably, the system that was studied provides health care to a wide spectrum of patients of all ages and from all geographic regions across the country. It covers active duty members of the military, retirees, reservists, and their family members, predominantly at primary care clinics and small, community-type hospitals.
In all, there were 62,326 positive blood cultures and 181,317 positive wound or abscess cultures during this time, and S. aureus was isolated from 12% of all blood cultures and 62% of all wound or abscess cultures.
The analysis focused on 2,643 blood and 80,281 wound or abscess infections with S. aureus.
Annual rates of methicillin-resistant bacteremia declined significantly, reversing the trend of increasing MRSA infections that had been reported before 2005. This decrease also has been noted in other national studies, Dr. Landrum and his colleagues said.
In addition, rates of MRSA bacteremia decreased significantly and in parallel for both hospital-acquired and community-acquired infections from 2005 to 2010. The incidence of community-acquired MRSA bacteremia dropped from 1.7 to 1.2 per 100,000 person-years, and that of hospital-acquired MRSA bacteremia decreased from 0.7 to 0.4 per 100,000 person-years. This trend also has been reported in other recent studies.
Rates of skin and soft-tissue MRSA infections followed the same pattern, declining significantly in both hospital-acquired (from 0.7 to 0.4 per 100,000 person-years) and community-acquired (from 76.8 to 64.0 per 100,000 person-years) cases.
The highest rates of community-acquired S. aureus bacteremia occurred in very young children and the elderly, but the highest rates of community-acquired S. aureus skin and soft-tissue infections occurred in young adults aged 18-24 years.
This study was only designed to characterize S. aureus infections and could not determine the reasons for these time trends. "Regardless of the etiology, the concurrent decreases in the rates of hospital-onset and community-onset MRSA bacteremia, coupled with the reduced prevalence of MRSA as a cause of community-onset S. aureus skin and soft-tissue infections, are intriguing observations that require further investigation," the investigators said (JAMA 2012;308:50-9).
This study was supported by the National Institute of Allergy and Infectious Diseases, the Global Emerging Infections Surveillance and Response Program of the Armed Forces Health Surveillance Center, the Navy and Marine Corps Public Health Center, the U.S. Department of Energy, and the U.S. Department of Defense. No financial conflicts of interest were reported.