A new study by the Centers for Disease Control and Prevention provides the first comprehensive look at the presence in the U.S. population of Staphylococcus aureus, including a potentially dangerous strain of the common bacterium. Lead author Matthew Kuehnert says that a study had never been done at this scale.

"We found that Staph aureus lives in the nasal passages of 90 million people in this country, or almost a third of all Americans," he said. 

The study, published in the Journal of Infectious Diseases, also finds that 2 million Americans carry an especially dangerous strain of the germ: methicillin-resistant Staphylococcus aureus. MRSA is a major problem in hospitals and has recently emerged outside medical institutions.

Matthew Kuehnert says understanding the ecology and diversity of staph can lead to better treatment.

"For instance, research into vaccines, colonization, eradication and infection control measures," he says and adds that researchers are learning that "not all Staph aureus are alike. So to target all staph aureus in the same way, he says would be not an efficient approach."

But, not everyone who is exposed gets sick. "There may be some isolates that cause disease more frequently," Mr. Kuehnert said.

MRSA is no more contagious than other staph infections, although the antibiotic resistant strains are far more difficult to treat.

Matthew Kuehnert says the prevalence of staph also differs among various segments of the population.

"Young school-age children were most likely to have staph aureus in their nose," he says, adding that the older children get, the less likely they are to have it. "But there were also differences in race ethnicity," he says.

MRSA was highest among women and those older than 60. Community associated MRSA was most common among young African Americans.

Mr. Kuehnert says the spread of staph infections can be reduced by simple hand washing. He also advises less use of antibiotics, to prevent development of new drug resistant strains of bacteria. And he says that when antibiotics are prescribed, the patient must take the full course.