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New vaccine reduces strains of bacteria most likely to cause severe infections

A new study of 16 Massachusetts communities found that 8 percent of children under age 7 carry antibiotic-resistant Streptococcus pneumoniae, a bacterium commonly found in healthy children but which presents a low risk of illness to them. While this rate is much higher than it would have been a decade ago, a new vaccine is reducing the presence of strains of the bacterium that can cause significant infection, according to the study which was supported in part by the Agency for Healthcare Research and Quality (HS10391).

Overall, researchers found that 190 (26 percent) of the children tested were carrying a strain of S. pneumoniae, and further testing of 166 of the samples indicated that many were resistant to a range of commonly used antibiotics. Since S. pneumoniae is a major cause of meningitis, bloodstream infections, and pneumonia, as well as ear and sinus infections every year in children under age 5, the risk to communities is that when serious, but rare infections do develop, antibiotic-resistant strains make the illnesses harder to treat.

Specifically, 33 percent of the tested samples were at least somewhat resistant to penicillin, 31 percent to trimethoprim/sulfamethoxazole, 22 percent to erythromycin, and 3 percent to clindamycin. In addition, 22 percent were resistant to at least three antibiotics. Children in group child care were four times more likely than other children to carry the antibiotic-resistant bacterium. Those who had recently used antibiotics and those who had a current respiratory infection were also more likely to carry resistant strains. Resistance among S. pneumoniae serotypes has been rising over the past decade throughout the United States, but infections with this bacterium are still effectively treated with available antibiotics.

This study is the first of its kind performed after introduction of a new vaccine to protect children from the seven most invasive strains of S. pneumoniae. These seven strains cause more than 80 percent of the serious infections. The rate of children who carried an antibiotic-resistant strain was the same in children who had received the vaccine and those who had not. However, immunized children were less likely to carry one of the seven more invasive strains, and thus they were at lower risk of contracting a serious illness.

The authors, led by Jonathan Finkelstein, M.D., M.P.H., and his colleagues at the Department of Ambulatory Care and Prevention, a unique research and teaching collaboration between Harvard Pilgrim Health Care and Harvard Medical School, caution that the study, conducted only 9 months after the vaccine was introduced, may not reflect the ultimate benefit of the vaccine as more children in the population are immunized.

Dr. Finkelstein and his colleagues analyzed background information from parents and nasal swab samples from 742 children in 16 geographically diverse communities in Massachusetts between March and May 2001. The children tested were visiting their pediatricians for a variety of reasons, including colds, ear infections and routine well care.

Beginning in 2000, the American Academy of Pediatrics recommended that all children 23 months and younger be immunized routinely with a new vaccine against the seven strains of S. pneumoniae that cause most of the serious infections from this bacterium. Dr. Finkelstein and his colleagues conclude that continued monitoring of antibiotic resistance is warranted both in the strains of bacteria covered by the vaccine and in those not covered.

For more information, see "Antibiotic-resistant Streptococcus pneumoniae in the heptavalent pneumococcal conjugate vaccine era: Predictors of carriage in a multicommunity sample," by Dr. Finkelstein, Susan S. Huang, M.D., M.P.H., James Daniel, M.P.H., and others, in the October 2003 Pediatrics 112(4), pp. 862-869.

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