The bug, called methicillin-resistant Staphylococcus aureus or MRSA, infected more than 94,000 Americans in 2005 and killed nearly 19,000, according to the CDC estimate. In comparison, about 17,000 people died of AIDS that year. The finding was published in Wednesday's Journal of the American Medical Association.
"This is a significant health problem. We should be very worried," Scott K. Fridkin, a CDC medical epidemiologist, told The Washington Post.
MRSA is a strain of a common bacterium that causes staph infections, which can generally be treated with antibiotics such as penicillin and amoxicillin. However, in recent years, the number of cases of antibiotic-resistant staph has been rising. On Monday, MRSA was blamed for the death of a 17-year-old Virginia boy, and Bedford County, Va., schools were closed for cleaning to prevent further infections.
Experts say that antibiotic overuse -- in people and in animal feed -- and patients who fail to complete their antibiotic regimens have contributed to the rise of antibiotic-resistant bacteria. This is because the antibiotics kill the more susceptible strains of bacteria and allow naturally resistant strains to flourish and multiply.
MRSA can live on the skin, where it causes relatively minor skin infections. However, if it makes it inside the body -- such as via an infected needle, an open wound or surgical equipment -- it can cause pneumonia and other life-threatening complications.
MRSA infections are particularly common in hospitals. However, almost 14 percent of the cases in the new study occurred outside of hospitals, in places like sports facilities and prisons.
In the study, the researchers tallied the number of infections at hospitals in nine states, identifying 5,287 cases of invasive MRSA and 998 deaths. These data suggest that MRSA hits 31.8 out of every 100,000 Americans, or more than 98,000 cases per year.
And this is only the invasive form of the bacteria -- even more people may harbor the milder skin infection. "It appears that the total burden of MRSA is much greater than what was estimated in this study," Los Angeles County Department of Public Health medical epidemiologist Elizabeth Bancroft, who wrote an editorial accompanying the study, told the Los Angeles Times.
Experts suggest several ways to begin to mitigate the problem. One -- curbing the unnecessary use of antibiotics -- could help slow down the emergence of antibiotic-resistant bacteria.
Other healthcare advocates suggest improving hygiene in hospitals. Some studies have shown that hospital staff wash their hands only half as often as recommended, according to the Associated Press. Some hospitals have also cut infections by isolating new patients until they are screened for MRSA.