man cleaning a high school locker room
Custodian Don Watkins disinfects a high school locker room in Sarasota, Fla., last week after three area students were diagnosed with staph infections. (Chip Litherland/The New York Times)

For years health authorities have warned of the growing threat posed by drug-resistant bacteria, but most of us have been half-listening. Not anymore.

A virulent strain of bacteria that resists many antibiotics appears to be killing more people annually than AIDS, emphysema or homicide, taking an estimated 19,000 lives in 2005, according to a study published last week in the Journal of the American Medical Association. The recent death of a 17-year-old high school football player in Virginia is a tragic reminder that methicillin-resistant Staphylococcus aureus, or MRSA, can prey on otherwise healthy people.

The best defense against the potentially deadly infection is common sense and cleanliness. "We need to reinvent hygiene for the 21st century,'' said Dr. Charles Gerba, professor of environmental microbiology at the University of Arizona at Tucson. "You go to a grocery store, and hundreds of thousands of people have touched those surfaces every day. Microorganisms are evolving very rapidly.''

Here are answers to common questions about community-acquired staph infections, or CA-MRSA.

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What does CA-MRSA look like?

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CA-MRSA is primarily a skin infection. It often resembles a pimple, boil or spider bite, but it quickly worsens into an abscess or pus-filled blister or sore. Patients who have sores that won't heal or are filled with pus should see a doctor and ask to be tested for staph infection. They should not squeeze the sore or try to drain it — that can spread the infection to other parts of the skin or deeper into the body.

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Who is at risk?

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The vast majority of MRSA cases happen in hospital settings, but 10 percent to 15 percent occur in the community at large among otherwise healthy people. Infections often occur among people who are prone to cuts and scrapes, such as children and athletes. MRSA typically spreads by skin-to-skin contact, crowded conditions and the sharing of contaminated personal items. Others who should be watchful: people who have regular contact with health care workers, those who have recently taken such antibiotics as fluoroquinolones or cephalosporin, homosexual men, military recruits and prisoners. Clusters of infections have appeared in certain ethnic groups, including Pacific Islanders, Alaskan Natives and Native Americans.

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What can I do to lower my risk of contracting MRSA?

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Bathing regularly and washing hands before meals is just a start. Wash your hands often or use an antibacterial sanitizer after you've been in public places or have touched handrails and other highly trafficked surfaces. Make sure cuts and scrapes are bandaged until they heal. Wash towels and sheets regularly, preferably in hot water, and leave clothes in the dryer until they are completely dry. "Staph is a pretty hardy organism,'' said Dr. Gerba.

Remind kids and teenagers that personal items shouldn't be shared with their friends, he added. This includes brushes, combs, razors, towels, makeup and cell phones. A teenager in Dr. Gerba's own family once contracted MRSA, he said, and he eventually traced the bacteria to her cell phone. She had shared it with a friend whose mother worked in a nursing home. Dr. Gerba went on to discover MRSA on the friend's cell phone and makeup compact and on a countertop in her home.

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Where does MRSA lurk?

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Staph bacteria may be found on the skin and in the noses of nearly 30 percent of the population without causing harm. Experts believe it survives on surfaces in 2 percent to 3 percent of homes, cars and public places.

But the bacteria are evolving, and the statistics may already underestimate the prevalence of MRSA. Be especially vigilant in health clubs and gyms — staph grows rapidly in warm, moist environments. The risks of infection and necessary precautions should be explained to student athletes, particularly those in contact sports who often suffer cuts and spend time in locker rooms. When working out at the gym, make sure you wipe down equipment before you use it. Many people clean just the sweaty benches, but Dr. Gerba notes that MRSA also has been found on the grips of workout machines. And if you have a scrape or sore, keep it clean and bandaged until it heals. Minor cuts and scrapes are the way MRSA takes hold.

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What is the single best thing I can do to protect myself from MRSA?

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Without question, people need to show far more respect for antibiotics. Misuse of antibiotics allows bacteria to evolve and develop resistance to drugs. But parents often pressure pediatricians to prescribe antibiotics even when they don't help the vast majority of childhood infections. When you do take an antibiotic, finish the dose. Antibiotic resistance is bad for everyone, but your body can also become particularly vulnerable to resistant bacteria if you are careless with the drugs.

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How do I find out more?

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One of the most useful Web sites is a MRSA primer from Mayoclinic.com. The Centers for Disease Control and Prevention offers a useful Q&A about MRSA in schools. A patient website called MRSA Resources lists a few stories of patients affected by MSRA. Recent Stanford University grad Nick Yee chronicles his struggle with MRSA on his Web site, which includes graphic videos of his wound and treatment. (I couldn't get through them.) And if you have the stomach for it, a number of people have — inexplicably — posted videos of their MRSA wounds on YouTube.