New estimates of infections by an antibiotic-resistant bacterium, methicillin-resistant Staphylococcus aureus (MRSA), have astounded experts, who had not considered it a major public health threat. Researchers conducted population-based surveillance at nine sites and extrapolated the 2005 data for the entire U.S. Recent fatal cases of invasive MRSA in children have also raised some concerns, although most deaths happened to people older than 65, and infections tended to occur at hospitals, rather than at schools and playgrounds.

Number of MRSA cases in 2005: 8,987

Number of in-hospital deaths: 1,598

Estimated number of deaths: 18,650

Number of AIDS deaths in 2005: 17,011

MRSA infections per 100,000 people: 31.8

In those 65 years and older: 127.7

In those between five and 17 years: 1.4

SOURCES: Journal of the American Medical Association, October 17, 2007; Centers for Disease Control and Prevention