The number of children sent to hospital with dangerous drug-resistant staph infections surged 10-fold in recent years, a U.S. study found.

Disease incidence increased from two cases to 21 cases per 1,000 hospital admissions from 1999 to 2008. Most infections were caught in the community, not in the hospital.

The study involved methicillin-resistant staph infections, called MRSA. These used to occur mostly in hospitals and nursing homes but they are increasingly showing up in other settings in children and adults. Recent evidence suggests hospital-acquired MRSA cases may be declining while community-acquired cases are becoming more common.

The results are "a good example of how something that is not unexpected remains alarming," said Dr. Buddy Creech, an infectious disease specialist at Vanderbilt University. He was not involved in the study.

The study involved 25 children's hospitals; the 10-fold increase in hospitalizations likely occurred nationwide, said Dr. Jason Newland, the lead author and an infectious disease physician at Children's Mercy Hospitals and Clinics and the University of Missouri-Kansas City.

Almost 30,000 children were hospitalized with MRSA infections at the hospitals studied during the 10-year period. Most had skin or muscle infections, and 374 youngsters with MRSA died. While Newland said it isn't clear if MRSA caused those deaths, it can be deadly and is blamed for more than 18,000 deaths in children and adults nationwide each year.

The study didn't examine whether deaths or the severity of infections increased.

The results were published Monday in the journal Pediatrics.

MRSA often begins as a pimple or boil on the skin. It can also spread to other parts of the body, including the bones or lungs, where it can cause pneumonia.

The study also found a coinciding increase in use of clindamycin, an antibiotic that comes in easy-to-use pills and liquid, and smaller increases for two other antibiotics.

Another drug effective against MRSA, vancomycin, is only available intravenously and its use decreased during the study.

Newland said the increasing use of clindamycin is concerning, because in some regions MRSA is already becoming resistant to the drug. Doctors need to use the antibiotic judiciously, he said.

Dr. Kenneth Alexander, the University of Chicago's pediatric infectious disease chief, said he agrees.

"Staph are incredibly cagey, and will ultimately find their way around any antibiotic in use," he said.

Research is needed to find other drugs that will work against MRSA, he said.