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ICAAC: Reducing Antibiotic Use Yields Differing Effects on Resistance


SAN FRANCISCO -- Reduced antibiotic usage in the United Kingdom appears to have halted resistance for respiratory pathogens, researchers reported here. However, Escherichia coli resistance tripled.

SAN FRANSICO, Sept. 28 -- Reduced antibiotic usage in Britain appears to have halted resistance for respiratory pathogens, researchers reported here.

At roughly the same time, however, Escherichia coli resistance to antibiotics has tripled in Britain, said another group.

The two studies, revealed at the Interscience Conference on Antimicrobial Agents and Chemotherapy, illustrate the difficulty in assessing the effect of reducing unnecessary antibiotic usage, said Alan P. Johnson, Ph.D., of the Health Protection Agency in London, who presented the E. coli research in a poster session.

He cited conflicting data depending on pathogen examined and the setting.

While antibiotic usage fell by 12% in England from 1997 through 2003, according to the European Surveillance of Antimicrobial Consumption, it has been an open question whether declining use of antibiotics would actually decrease resistance once it had been established.

Dr. Johnson and colleagues found that E. coli bacteremia resistant to the antibiotic Cipro (ciprofloxacin) tripled from 6.4% in 2001 to 19.6% in 2005. Previous research indicated 2.1% Cipro resistance in England in 1995 indicating a "quite dramatic" and steady rise for the nation.

On the other hand, key resistances in community-acquired respiratory pathogens in the United Kingdom, such as Streptococcus pneumoniae insusceptible to penicillin, showed no change from 1999 to 2006, reported Rosy Reynolds, Ph.D., of the British Society for Antimicrobial Chemotherapy in Birmingham, England, and colleagues.

"We think it's probably related to antibiotic consumption but it's very difficult to prove that," Dr. Reynolds said in her poster presentation.

Dr. Reynolds and colleagues analyzed respiratory pathogen isolate samples from 20 centers in the Britain over seven winter seasons.

Resistance in S. pneumoniae was:

  • 5.9% for penicillin,
  • 10.9% for erythromycin,
  • 6.4% for tetracycline, and
  • 5.9% for Cipro but none showed significant increases or decreases over time.

Resistance in Haemophilus influenzae was:

  • 14.7% for beta-lactamase,
  • 99.0% for erythromycin,
  • 2.3% for tetracycline, a significant drop (odds ratio 0.49, P=0.005), and
  • 0.1% for Cipro.

Resistance in Moraxella catarrhalis was:

  • 93.3% for beta-lactamase, a significant rise (OR 1.83, P=0.006),
  • 0.2% for erythromycin,
  • 0.2% for tetracycline, and
  • 0.2% for Cipro.

Dr. Reynolds said the study was well powered to find a doubling over five years, which past studies on resistance have typically not had, and that it supports continued efforts to decrease unnecessary antibiotic use. "There might be something in it."

Conversely, E. coli showed a sharp rise in antibiotic resistance over the past few years. Dr. Johnson and colleagues looked at isolates susceptibility data from about 150 hospital microbiology laboratories recorded in a British national database.

Isolates resistant to extended-spectrum cephalosporins increased from 1.5% in 2001 to 9.0% in 2005. More than 30% of Cipro-resistant strains are also resistant to extended-spectrum cephalosporins, about three times more than in 2001 (30.7% versus 10.7%).

Interestingly, more bacteremia isolates resistant to both Cipro and extended-spectrum cephalosporins were reported from men (58.3% versus 41.7% from women).

Since the two antibiotics are the first line therapies for E. coli bacteremia and there are few agents in the developmental pipeline, the findings are cause for concern, Dr. Johnson said.

It also "has important implications for empiric treatment" in that physicians may choose carbopenem antibiotics when treating patients before susceptibility data is back from the laboratory, he said.

Dr. Reynolds' study was part of a surveillance program sponsored by Abbott, Aventis, Bayer, GeneSoft, GlaxoSmithKline, Merck Sharp & Dohme, and Wyeth. Some authors were employees of Merck Sharp & Dohme and Wyeth.

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