Infections caused by antibiotic-resistant bacteria are far more widespread than scientists previously thought and might be killing more than 19,000 people a year in the United States, according to a study published today.

Of the nine sites that researchers examined, Baltimore had the highest rate of infection by invasive methicillin-resistant Staphylococcus aureus, commonly known as MRSA. But health officials said the city was more urbanized than the other sites, which could account for much of the difference.

Experts said this study of MRSA, the most comprehensive to date, highlighted the growing danger of these antibiotic-resistant germs. Patients who contract MRSA are more likely to die than those who contract many other bacterial infections.

"This is the first time that we've been able to measure the number of infections," said the study's lead author, Dr. R. Monina Klevens, an epidemiologist with the federal Centers for Disease Control and Prevention. "We were surprised that the rates were so high. It's a call to action."

The study, published in today's Journal of the American Medical Association, is the first on such a large scale to analyze the incidence of drug-resistant infections in the community at large, as well as in hospitals, where it has traditionally been studied.

The issue recently surfaced locally when four Anne Arundel County high schools reported 50 staph infections - at least one of which was drug-resistant.

Today's study, sponsored by the CDC and conducted jointly by researchers across the country, analyzed data from 2005 and found 8,987 cases of invasive MRSA.

Overall, this translated to 31.8 cases per 100,000 people, about twice as high as the previous estimate, according to Klevens.

The infection rates were highest among people older than 65 (127.7 per 100,000) and among African-Americans (66.5 per 100,000).

Of those infected with MRSA, almost 1,600 died, about 18 percent of the total. Extrapolating those figures to the entire U.S. population, researchers said some 94,000 people might be infected, with 19,0000 deaths.

"This establishes that there are large numbers of these infections," said Dr. Barry Farr, a retired epidemiologist from the University of Virginia School of Medicine and a longtime critic of U.S. efforts to fight MRSA and other fast-spreading antibiotic-resistant bacteria.

Farr noted that a CDC analysis four years ago found that MRSA infection rates had grown 32-fold between 1980 and 2003 - rising from 2 percent of all staph infections to 64 percent.

'Nationwide epidemic'

"This is way out of control," Farr said. "It's egregious. It's a nationwide epidemic."

He said that the latest study probably underestimates the actual number of cases, because it counted only those confirmed by a blood test. Many more people probably were infected but either didn't seek treatment or weren't specifically tested.

Several European countries, including the Netherlands and Denmark, have significantly lowered MRSA rates through widespread testing of patients and health care workers, emphasis on proper hygiene, and aggressive treatment of those found to be infected.

But in the United States, many hospitals and clinics have not implemented these measures. Farr and other critics say the CDC, which is responsible for providing infection control guidelines, should do more.

"A large number of people are paying a large price because nothing has been done in most health care facilities," Farr said.

Several Baltimore hospitals have tightened infection control practices over the past two years, including Johns Hopkins Hospital, the University of Maryland Medical Center and Franklin Square Hospital.

Nancy Fiedler, a spokeswoman for the Maryland Hospital Association, said the state's medical centers are doing a good job of fighting MRSA. But she agreed that more should be done.

"It's a big problem in Maryland. It's going to be a problem if we don't recognize its scope," said Dr. Margaret Toth, an epidemiologist with the Delmarva Foundation, which is organizing and funding infection control programs in Maryland hospitals.

Michael Bennett, the director of Coalition for Patients' Rights in Maryland, a group that advocates for better infection control, is critical of efforts here and elsewhere.

"Every hospital, every clinic, every dialysis center should be doing active detection and isolation to identify antibiotic resistant infections," he said.

It is not clear why MRSA rates in Baltimore are so much higher than the other eight study sites. Researchers found that in Baltimore, 116.7 of every 100,000 people were infected with invasive MRSA. The next highest site was Davidson County, Tenn., with 53 per 100,000.

More Baltimoreans contracted the infection in the community, at 62.9 cases per 100,000, than in hospitals, at 19.7 cases per 100,000.

Laura Herrera, chief medical officer for the Baltimore City Department of Health, noted that the other sites in the study were not strictly urban areas.

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.

'Superbug' infections

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.

david.kohn@baltsun.com