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NEW YORK (Reuters Health) Dec 08 - In southern Israel, where antipneumococcal conjugate vaccines have not been introduced, researchers have documented the presence of penicillin-nonsusceptible non-vaccine type Streptococcus pneumoniae strains in children with acute otitis media.
Dr. Nurith Porat of Soroka University Medical Center in Beersheva, and colleagues, explain in the December 15th issue of The Journal of Infectious Diseases that after the introduction in 2000 of a pneumococcal conjugate vaccine, there was a shift toward carriage of pneumococcal strains that had not been included in the vaccine.
Dr. Porat's group used pulsed-field gel electrophoresis to analyze nasopharyngeal and middle ear isolates obtained from children in Israel between 1998 and 2003, and from children in Costa Rica between 1998 and 2001.
In the Israeli samples, all from children under the age of 5 years, the researchers studied 46 nasopharyngeal and middle ear fluid isolates expressing serotype 11A and 45 middle ear fluid isolates expressing serotype 15B/C. In addition, using middle ear fluid samples obtained from young children in Costa Rica, the researchers analyzed 57 isolates expressing serotype 19F.
Genotypic analyses of the Israeli samples revealed "two clusters expressing non-vaccine type serotypes with a genetic background closely related to that of two vaccine type clones," according to the article.
One was documented in a cluster of isolates expressing serotype 11A, and the other in a cluster of isolates expressing serotype 15B/C. Both clones were more common among Bedouin children than among Jewish children.
According to the article, the electrophoresis patterns of the first clone "were almost indistinguishable...from those of the penicillin-resistant serotype 9V/14 international clone, which was first identified in Spain and France," and has become widely disseminated around the world. The pattern of the second clone was closely related to that of the serotype 19F clone recovered from the Costa Rican children.
"Penicillin-nonsusceptible pneumococcal clones of serotypes not related to those included in the 11-valent conjugate vaccines may derive from capsular transformation of vaccine-related serotypes," the authors speculate.
"This phenomenon, although seemingly rare at present, can have implications for the long-term effectiveness of the conjugate vaccines," they conclude.
J Infect Dis 2004;190:2154-2161.
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