Most are mild, like pimples and boils, and don't require antibiotic treatment. But they can also be serious, such as surgical wound infections or pneumonia. A type of antibiotic related to penicillin has been used for more than 50 years to treat such serious infections. MRSA are the resistant bacteria that now don't respond to those antibiotics.

Health care providers aren't required to report MRSA, so public health authorities don't keep a clear count of cases. But the CDC says some estimates claim as many as 100,000 people are hospitalized each year with MRSA infections. Efforts are under way to improve surveillance and get a more precise count.

"There are some new drugs that the pharmaceutical industry has developed — $1,000 for a 10-day course. Maybe that's an underestimate. Expensive new therapies have been developed that do give us a few more options. But it's still a situation where the commonly used drugs are not effective. What happened is that MRSA changed itself, developed new ways to express resistance. These new ways . . . made it better able to survive and transmit," Samore said.

In the hospital, MRSA was typically confined to the sickest patients, usually those with chronic illnesses, he said. With new MRSA strains, infections are occurring in otherwise healthy people, as well as those who are already sick.

Like all staph infections, it can be passed with skin-to-skin contact. Often, skin infections are particularly severe. And sometimes outbreaks of infections are associated with prisons, athletic groups and other situations where there's close contact. That happened last year in Utah, when wrestlers from several schools developed skin rashes and infections.

Staph infections were typically treated with the "cillin" drugs. The fact that MRSA is cillin-resistant meant doctors had to turn to the second line of drugs, such as erythromycin, for staph aureus. "Now we're seeing that change as well. That little piece of good news is starting to dry up," Samore said. "They're getting more resistant to that, as well."

The cause of antibiotic resistance, MRSA or not, is simply overuse of antibiotics. That means taking antibiotics when they're not needed or helpful, as is the case when a person who has a virus is treated with antibiotics (they kill only bacteria) or when a person starts a course of properly prescribed antibiotics and then doesn't finish it, which lets some of the bugs change and evolve. Lots of people over the years have also self-medicated, using an antibiotic that's not the right one for the bacteria it's trying to kill — if it is a bacterium.

The net effect is the creation of what is becoming a medical nightmare. Illnesses that antibiotics used to work on sometimes thrive now in spite of treatment.

There are a lot of misconceptions about antibiotics, Samore said.