WASHINGTON — The number of methicillin-resistant Staphylococcus aureus infections has dramatically risen in recent years, and more and more cases are community acquired, at least in one emergency department, Dr. Mary-Claire Roghmann said at the annual Interscience Conference on Antimicrobial Agents and Chemotherapy.
“We had more than a doubling [in new cases of methicillin-resistant S. aureus] from 2003 to 2004,” said Dr. Roghmann, the hospital epidemiologist for Veterans Affairs Maryland Health Care System. The ED at Baltimore VA Medical Center sees about 85 patients per day.
Tipped off by ED physicians that more MRSA cases seemed to be coming in, Dr. Roghmann and her colleagues identified patients with MRSA isolated for the first time for that patient from a culture taken in the ED. They discovered an increase in new cases of MRSA in the ED, starting with 0.2 new MRSA cases per 1,000 ED visits in 2001 and more than doubling from 1.1 to 2.6 new MRSA cases per 1,000 ED visits from 2003 to 2004.
To learn more about these cases, the researchers accessed data from the VA's patient records system. They excluded any patients with a history of MRSA prior to the ED visit. Specifically, they looked at type of infection, antibiotic susceptibility, and risk factors for hospital-acquired MRSA, said Dr. Roghmann, also of the University of Maryland in Baltimore.
They defined type of infection as a positive culture from the site and also signs and symptoms of infection at the site. Risk factors for hospital-acquired MRSA infection included history of hospitalization, surgery, dialysis, or residence in a long-term care facility in the last year. Patients were excluded if they had a percutaneous medical device or indwelling catheter at the time of the culture. Patients without any of these risk factors were determined to have community-acquired MRSA.
In 2004, there were 90 patients who met the criteria for newly acquired MRSA based on cultures from the ED. “Of these, 58% had community-acquired MRSA. The vast majority of patients had skin and soft tissue infections,” Dr. Roghmann said at the meeting, which was sponsored by the American Society for Microbiology.
In terms of antibiotic susceptibility, community-acquired MRSA cultures were more likely than were health care-acquired MRSA cultures to be susceptible to clindamycin and tetracycline.
The emergency physicians had also indicated that there seemed to be more skin and soft tissue infections. To determine whether there was also an increase in skin and soft tissue infections during the same time period, the researchers looked at visits to the ED with ICD-9 codes specific to those infections.
“There has been almost a doubling of the incidence rate of skin and soft tissue-related visits to our ED during this period,” said Dr. Roghmann. The number of these visits per 1,000 ED visits rose from 26 in 2001 to 54 in 2003.