For several years, health professionals have been concerned about the rise in infections from methicillin resistant staphylococcus aureus, or MRSA – a bacteria that’s resistant to several of the antibiotics generally used to treat staph infections. CDC estimates that in 2005, there were more than 94,000 MRSA infections in the US, and more than 18,000 of those patients died. The numbers are probably much higher now.

A study just published in the journal Pediatrics gives us new information about staph infections in hospitalized US children and how they’re being treated. The results show a disturbing increase in the number of MRSA cases, and suggest that we might be creating conditions that’ll encourage the bacteria to evolve further resistance and become an even greater threat.

The researchers – Joshua C. Herigon, Adam L. Hersh, Jeffrey S. Gerber, Theoklis E. Zaoutis and Jason G. Newland – analyzed data about patients under the age of 18 who were admitted to a hospital and diagnosed with an Staphylococcus aureus infection from 1999 – 2008. The data came from the Pediatric Health Information System database maintained by a collaborative of not-for-profit, tertiary care pediatric hospitals from across the US, and the researchers used data from the 25 hospitals that had submitted complete data for the study period.

The researchers examined 2.4 million patient discharges and found that 3% of the children had been diagnosed with S aureus infections, and the most common infection type (39%) was skin and soft tissue infections. The most striking finding has to do with the incidence rate (emphasis added):

During the 10-year study period, the incidence of S aureus infection more than doubled, increasing from 14.8 per 1000 admissions in 1999 to 35.7 per 1000 admissions in 2008 … The incidence of MRSA infections during this period increased 10-fold, from 2.0 cases per 1000 admissions in 1999 to 20.7 cases per 1000 admissions in 2008.

The authors note that while we used to see MRSA infections mainly in people who had a history of repeated hospitalizations or extensive antibiotic treatments, we’re now seeing more community-associated MRSA (CA-MRSA) infections in previously healthy individuals. They don’t delve into the implications for prevention efforts, but this can hardly be good news. Hospitals have found it hard to get their staffs to fully comply with infection-prevention protocols, but at least they have a pretty good idea what they need to do to keep infections from spreading, and the capability to do it. Preventing the spread of MRSA in a wide range of community environments, from day-care centers to high-school gyms, seems like a far more daunting task.

This study also focuses on the antibiotics used to treat S aureus infections in the 64,813 cases identified. Researchers found that the use of clindamycin, an antibiotic that’s active against MRSA, increased threefold; it was used in 21% of the identified S aureus infection cases in 1999, and 63% in 2008. They point out that resistance to clindamycin is increasing in some regions of the country, and state that the surge in clindamycin use “has the potential to facilitate the development of resistance among circulating clindamycin-sensitive CA-MRSA strains.”

The authors recommend that clinicians monitor their institutions’ antibiograms. These summaries of the antibiotic susceptibility of the bacterial strains found in the institution’s patients can help providers prescribe antibiotics most likely to be effective in their particular patient populations. However, Herigon et al cite a study by researchers from Brown University and Rhode Island Hospital that found more than 60% of the residents and fellows in their training program who responded to a survey never used the hospital’s cumulative antimicrobial susceptibility data.

This study provides more evidence that MRSA is spreading and evolving more quickly than our antibiotics and prevention and treatment practices are. That’s not good news.

For more on MRSA, Maryn McKenna is an excellent resource – check out her Superbug blog and new book Superbug: The Fatal Menace of MRSA.