Kids who get lots of antibiotics from their doctors are more likely to harbor the MRSA superbug, although it's still rare, a new study of British youngsters has found.

While that doesn't prove the drugs are to blame for the antibiotic-resistant bacterium, it would make biological sense, researchers say.

"This just provides more evidence to support redoubling our efforts to decrease antibiotic use," Dr. Daniel J. Diekema, who was not involved in the new work, told Reuters Health.

MRSA, or methicillin-resistant Staphylococcus aureus, first arrived in the U.S. in the 1960s. But it wasn't until 1980, when it infected a burn victim in a Seattle hospital and caused a devastating outbreak, that doctors realized how serious the situation really was.

It is estimated that in 2005, the bug caused severe infections in nearly 95,000 Americans and killed more than 18,500 of them.

While infections caught in hospitals have been declining in recent years, there is less certainty about those contracted outside hospitals -- so-called community-acquired MRSA.

"It remains a major public health problem, but the dramatic increase that we saw during the last decade seems to have leveled off in many areas and may be decreasing in some," said Diekema, an expert in infectious diseases at the University of Iowa in Iowa City.

To get a better idea about how MRSA infections arise outside of hospitals, Canadian researchers looked at data from more than 400 doctors' offices in the UK.

They'd already shown that adults with several antibiotic prescriptions were more likely to harbor MRSA later on, so this time they focused on kids who'd gotten the diagnosis between 1994 and 2007.

There were 4.5 MRSA cases per 100,000 children every year in the UK, although it wasn't clear from the data whether the children had active infections or just carried the bacteria on their skin, where they are harmless.

"In general, only a minority of people who carry MRSA go on to become infected," Diekema explained.

Of 297 children who tested positive for MRSA, more than half (53 percent) had been prescribed at least one antibiotic between 30 and 180 days before the diagnosis (the last 30 days were excluded to make sure the drug hadn't been used to treat

MRSA).

By contrast, only 14 percent of more than 9,000 kids who'd visited the same doctors but didn't have MRSA had recently been taking antibiotics.

After accounting for differences between the two groups of children -- such as hospital stays or other diseases they might have -- that amounted to a three-fold difference in the risk of harboring MRSA.

And the more antibiotics the children had been given, the more likely they were to be carrying the resistant bug. Those who got four or more prescriptions, for instance, had 18 times the risk of MRSA.

"Observational studies like this really can't prove causality," said Diekema. But he added that it was biologically plausible that antibiotic use would fuel the growth of resistant bacteria.

On the other hand, nearly half of the children who had the bug hadn't received any antibiotics in the half year before their diagnosis, the Canadian team reports in the Archives of Pediatrics & Adolescent Medicine.

"This is an intriguing observation that we expect will generate some research into the mechanism of MRSA development," said Samy Suissa, of McGill University in Montreal, who led the new research.

In an email, he said it's important to curb the inappropriate use of antibiotics, which fight bacteria but have no effect on viruses.

"Parents should freely discuss with their physician if they feel that antibiotics may be overprescribed," Suissa told Reuters Health.

SOURCE: bit.ly/qHXfTt Archives of Pediatrics & Adolescent Medicine, online August 1, 2011.

United kingdom