New cases of a drug-resistant bacterial infection called MRSA have risen by 90 percent since 1999. Researchers reported this week that they have been mostly acquired outside hospitals.

Two new strains of methicillin-resistant Staphylococcus aureus (MRSA) were circulating among patients and they were not similar to the strains that were seen normally in hospitals.

Data analyses on lab tests collected from a national networkof 300 microbiology laboratories in the United States was done by Ramanan Laxminarayan of Princeton University in New Jersey and his colleagues.

They wrote in a report which is published in the journal Emerging Infectious Diseases, “We found during 1999-2006 that the percentage of S. aureus infections resistant to methicillin increased more than 90 percent, or 10 percent a year, in outpatients admitted to U.S. hospitals.”

The team found that many more people were diagnosed with community-acquired strains which were not replacing the known hospital strains.

MRSA is the most common cause of hospital-acquired infections. Other places where it can be picked up from are schools, fitness centers and similar areas.