The seven other sites were the state of Connecticut; the metropolitan areas of Atlanta, Denver, San Francisco and Portland, Ore.; Monroe County, N.Y.; and Ramsey County, Minn.
Herrera said MRSA infection rates are likely to be lower in suburbs and rural areas, skewing the data so that Baltimore numbers appear higher in comparison.
Herrera also said illegal drugs might be a factor in the Baltimore numbers. Most experts say that Baltimore has 30,000 to 60,000 intravenous drug users, a group that is at higher risk for MRSA infections through needle sharing and generally unhealthy lifestyles.
But she said she is not sure what caused the city's higher rates. She is talking with the city's 11 hospitals to come up with more effective ways to decrease infection rates.
But the problem is not limited to the city. Over the past four months, 50 students and staff members at four Anne Arundel County high schools have been infected with the staphylococcus bacteria. At least one of these infections was caused by MRSA. The other 49 weren't specifically tested, officials said, so there's no way to know for sure.
Elin Jones, a spokeswoman for the Anne Arundel County Department of Health, said the agency was working with schools and the parks and recreation department to institute better hygiene in educational and athletic facilities.
Since Oct.12, the county Health Department has received about four reports a day from parents who think their children might have staph infections. Nevertheless, Jones said, the department had no plans to implement widespread testing of students and staff.
Today's issue of JAMA featured another study on antibiotic-resistant bacteria, this one from University of Rochester scientists who identified a new antibiotic-resistant strain of Streptococcus pneumoniae, a bug that commonly causes ear infections in children.
Examining 212 children with ear infections, they found strep in 59. Of those, nine had a new drug-resistant strain, which was impervious to all 18 antibiotics approved for use in children.
Four of those children required ear surgery, while the other five were cured with levofloxicin, a powerful antibiotic that is not approved for children in the United States. The doctors prescribed the drug "off label," with parental permission.
"We've identified a superbug," said the lead researcher, Dr. Michael Pichichero, a professor at the University of Rochester School of Medicine. He said the study underscores the need to control use of antibiotics, a practice that also contributes significantly to the spread of MRSA.
He said that it's likely the new strain exists elsewhere, and that if not, it could easily spread.