ATLANTA, Oct. 16 — Nearly 19,000 people died in the United States in 2005 after being infected with virulent drug-resistant bacteria that have spread rampantly through hospitals and nursing homes, according to the most thorough study of the disease’s prevalence ever conducted.

The government study, which is being published Wednesday in The Journal of the American Medical Association, suggests that such infections may be twice as common as previously thought, according to its lead author, Dr. R. Monina Klevens.

If the mortality estimates are correct, the number of deaths associated with the germ, methicillin-resistant Staphylococcus aureus, or MRSA, would exceed those attributed to H.I.V.-AIDS, Parkinson’s disease, emphysema or homicide each year.

By extrapolating data collected in nine places, the researchers estimated that 94,360 patients developed an invasive infection from the pathogen in 2005 and that nearly one of every five, or 18,650 of them, died. The study points out that it is not always possible to determine whether a death is caused by MRSA or merely accelerated by it.