NEW YORK (Reuters Health) - Bloodstream infections caused by the MRSA superbug may be on the decline in communities across the U.S., according to a large study of military personnel.

Previous data from the Centers for Disease Control and Prevention show a drop in infections contracted in healthcare settings. But the trajectory of community-onset MRSA, short for methicillin-resistant Staphylococcus aureus, is less clear.

The bug - a strain of bacteria that can't be killed by certain common antibiotics - is estimated to have caused severe illness in nearly 95,000 Americans in 2005 alone, killing more than 18,500 of them. MRSA can attack several part of the body, but bloodstream infections are usually the most feared.

"Those are very serious infections with a mortality rate of 20 percent," said Dr. Michael David, a MRSA expert at the University of Chicago, who was not involved in the new study. "The fact that those are going away is very welcome news."

Still, he cautioned, the study might not reflect the overall picture in the U.S. because it's based on data from people receiving care within the Department of Defense healthcare system.

While those people - more than 9 million a year during the study period from 2005 to 2010 - included both retirees and family members of duty personnel, they were all insured and might be healthier than the average American.

And the study, published in the Journal of the American Medical Association, doesn't capture MRSA cases spotted outside the military health system, meaning it probably underestimates the rate of infections.

MRSA bloodstream infections fell in the community and in hospitalized patients alike. In the community, the rate dipped from 1.7 per 100,000 people in 2005 to 1.2 per 100,000 in 2010.

"This isn't saying we don't have to worry about MRSA anymore," said Dr. Clinton Murray, of the San Antonio Military Medical Center in Fort Sam Houston, Texas, who led the work.

"There is still a heavy burden," he told Reuters Health.

In fact, a study just published by the University of Chicago's David suggests the financial part of that burden may amount to billions of dollars in healthcare spending and lost productivity.

It's unclear why the bug would be on the retreat, but both David and Murray say it's possible control programs aimed at patients both in and outside of hospitals may have played a role.


Staph bacteria may also invade the skin, where they can cause big, red boils, or abscesses. Although such bug attacks are far less dangerous than bloodstream infections, they are also much more common.

When Murray and his colleagues looked at MRSA skin infections, the picture grew murkier.

Overall, the rates in the community declined during the study, but statistical tests showed that change could have been due to chance alone. On the other hand, the proportion of Staph skin infections caused by MRSA, as opposed to its non-resistant cousins, showed a robust drop from 62 percent to 52 percent.

"Fifty-two percent is still a lot," David told Reuters Health. But, he added, the new development could be a sign that some MRSA bacteria have jettisoned the gene that made them resistant to antibiotics in the first place.

He said such strains have already been found in the lab, although at this point "it's completely hypothetical."

SOURCE: Journal of the American Medical Association, online July 3, 2012.