THURSDAY, DECEMBER 28, 2000                            HEALTH                         San Francisco Chronicle        A9

Bacteria More Resistant To Antibiotics, Study Says
Researchers blame overuse of medication


One of nature's most common -- and dangerous -- disease-causing bacteria is developing antibiotic-resistant strains at an increasing rate, the latest evidence that overuse of "wonder drugs" is causing them to lose their effectiveness.

A report in today's issue of the New England Journal of Medicine found that the rate of multidrug resistance for the microbe Streptococcus pneumoniae had increased from 9 percent to 14 percent between 1995 and 1998. Streptococcus pneumoniae is the most common cause of bacterial meningitis, pneumonia and inner ear infections in the United States.

"The emergence of S. pneumoniae with antimicrobial resistance is a matter of great concern," said the research team, led by Cynthia Whitney of the Centers for Disease Control and Prevention. "Multidrug-resistant pneumococci are common and are increasing."

As recently as the 1930s, the fatality rate from pneumonia in the United States stood at 35 percent. With the introduction of antibiotics, the rate began to drop in sharp increments until it reached 5 percent to 8 percent with the introduction of penicillin.

The CDC team collected 12,045 samples of Streptococcus pneumoniae between 1995 and 1998 from a population of 16.5 million spread throughout the country. During that period, the rate of resistance to penicillin rose from 21 percent to 25 percent, the report said, but the rate of resistance to three or more classes of drugs rose much more sharply - from 9 percent to 14 percent.

The study found a higher proportion of penicillin-resistant bacteria among children and white Americans than among adults and black Americans, statistics the team said probably reflected whites' easier access to antibiotics and parents' greater likelihood of dosing their children with drugs.

  Furthermore, the report said, although bacterial strains "that are susceptible to penicillin are rarely resistant to another agent," strains "that are resistant to penicillin are likely to be resistant to multiple other agents."

The chief culprit in microbial resistance is overuse of antibiotics, the team said, and in an editorial accompanying the study, Richard Wenzel and Michael Edmond of Virginia Commonwealth University noted that approximately 25,000 tons of antibiotics are consumed each year in the United States, about half by humans and the rest by livestock and agriculture.

"This enormous level of use of antibiotics has great potential for selecting for, or enhancing the growth of resistant strains," Wenzel and Edmond wrote. "Probably half of such uses are inappropriate," they added, citing "needless treatment" of viral infections with antibiotics.

Researchers estimate that half of all antibiotics prescribed by doctors are unnecessary, given to patients with viral infections or other ailments that the drugs will not fight.

Bacterial infections that resist antibiotics are difficult and expensive to treat, often requiring multiple drugs, unusually long courses of therapy and in some cases hospital stays. In elderly people or those with diseases that weaken the immune system like leukemia or AIDS, drug-resistant infections can be fatal, especially when the bacteria invade the bloodstream.

The CDC team argued for "expanded efforts to reduce the unnecessary use of anti-microbial agents," targeting of specific microbes and increasing reliance on vaccines for high-risk adults and for children.

The New York Times contributed to this report.

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