Scanning electron micrograph of clusters of methicillin-resistant Staphylococcus aureus (MRSA) bacteria. (Annie Cavanagh, Wellcome Images)

Patients, staff and visitors all help spread drug-resistant staph bacteria within hospitals, a new study that precisely tracked transmission suggests.

MRSA, or methicillin-resistant Staphylococcus aureus, is a strain of Staph that has become resistant to most types of antibiotics.

The superbug rarely caused problems in healthy people, and is most often seen in hospitals.

People with long-term illnesses or who have compromised immune systems are at increased risk of infections. MRSA usually causes skin infections, but if it gets into the body then blood poisoning or pneumonia may result.

Zooming in on infections

In Friday's issue of the journal Science, researchers from Britain's Wellcome Trust Sanger Institute used specialized gene sequencing equipment to find precise differences in strains of MRSA. The researchers say the findings are important for public health programs that aim to reduce the number of people sickened by MRSA.

"We wanted to test whether our method could successfully zoom in and out to allow us to track infection on a global scale — from continent-to-continent, and also on the smallest scale — from person-to-person," study author Simon Harris of the Sanger Institute in Cambridge, U.K., told reporters.

Until now, researchers were unable to pick up on these tiny genetic differences, so it was unclear how infections spread.

The study focused on 62 MRSA samples, including 42 samples taken from people worldwide who were infected with MRSA between 1982 and 2003, and a second set of 20 samples from patients at one hospital in northeast Thailand. They were all infected with seven months of each other.

Of the 20 Thai patients who were infected with a strain called ST239, only five shared exactly the same infection, and they were all isolated within a few weeks of each other. Bacteria from patients housed in other parts of the hospital were much less similar.

'Extra ammunition' for infection control

This cemented thinking that two different types of MRSA has been introduced to the hospital separately, said study co-lead author author Ed Feil of biology and biochemistry department at the University of Bath in England.

"I think that this tool will provide extra ammunition to identify routes of transmission for MRSA, so infection control can be concentrated more on areas that appear to be letting MRSA transmit between patients or between hospitals," said co-author Dr. Sharon Peacock, a professor of clinical microbiology at the University of Cambridge in England.

The research is "very interesting," said Dr. Michael Gardam, head of infection prevention at Toronto's University Health Network, but he questioned its value for hospital infection control.

The findings offer a better way of measuring how MRSA spreads, but this information " will not make people wash their hands more, it's not going to change the way we design hospitals …it's not really going to change what I'm doing," Gardam said.

All patients entering the University Health Network's three hospitals in Toronto are tested for MRSA, as do some hospitals in Britain and the U.S.

These MRSA swab doesn't give details about the subtype, said Dr. Buddy Creech, a Vanderbilt University infectious disease specialist who wasn't involved in the study.

The tests used in the study take a few weeks about $300 US per sample, which limits is value outside a research setting. Creech said a similar study is under way to better understand MRSA's genetics in hopes of developing a vaccine.

With files from The Associated Press, The Canadian Press