WASHINGTON - A county in southern Virginia closed its 21 schools on Wednesday to clean them to prevent the spread of a dangerous bacterial infection that killed a 17-year-old high school student, officials said.

The student died this week from a drug-resistant staph infection known as Methicillin-resistant Staphylococcus aureus, or MRSA, which has become a worrisome public health issue nationwide.

Schools in Bedford County were closed to allow officials to carry out a thorough cleaning in an effort to get rid of the bacteria responsible for these infections, according to Charles Pyle, spokesman for the Virginia Department of Education.

The two schools of a small rural district in Rappahannock County in the northern part of the state closed for a day last week for a similar cleaning due to MRSA concerns, Pyle added.

Robert Parker, spokesman for the Virginia Department of Health, said three MRSA outbreaks have been reported so far this year in the state, making 2007 no worse than prior years.

"VDH (Virginia Department of Health) considers it to be sort of ubiquitous but not a public health threat any more today than it was yesterday or the day before," Parker said.

Pyle said the state education department is encouraging school districts statewide to contact local health authorities on steps to minimize the risk of infections.

Research published in the Journal of the American Medical Association on Tuesday showed an estimated 19,000 Americans died from MRSA in 2005, the most recent year for which figures were available, and made 94,000 seriously ill.

This was much more than previous estimates. About 85 percent were caught in a hospital or health care facility but the infection is also found in the community.

Staph bacteria typically are found on the skin or in the nose of about a third of the population, health officials said. They cause pimples or rashes but occasionally can cause severe infections in the lungs, kidneys and other organs.

The U.S. Centers for Disease Control and Prevention estimates that 1 percent of the population carries MRSA, often with no symptoms. The CDC has no data on school closures because of MRSA infections.

In schools, staph infections are prone to spread in places like locker rooms through shared personal items like towels and athletic gear, officials said. State officials urged students and others in schools to wash their hands regularly and take other precautions like not sharing personal items.

Even MRSA infections are treatable with antibiotics but doctors need to know to use the correct drugs.