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Increase of S. pneumoniae 19A serotype reported in Canada
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Following the introduction of the seven-valent pneumococcal vaccine (PCV7, Prevnar, Wyeth) in Canada, there has been a significant decrease in vaccine serotypes 23F, 6A and 14, but there has also been a corresponding increase rise in the nonvaccine serotype 19A, according to data presented here.
“Further study is required to determine the origin of 19A MDR Streptococcus pneumoniae and the role of antibiotic vs. immune-selected pressure in selecting this clone out,” said Susan Poutanen, MD, of the Canadian Bacterial Surveillance Network in a presentation here.
Poutanen presented research compiled by the network between 1995 and 2007. She said there was a mean of 2,044 S. pneumoniae samples per year. The researchers noted that before the introduction of the vaccine, the rate of MDR S. pneumoniae was about 8%, which was similar to post- vaccine use, about 7%.
The most striking difference before and after the introduction of this vaccine was the emergence of the MDR S. pneumoniae 19A serotype – about 5% before the vaccine compared with 15% post-PCV7 use.
In researching multilocus sequence typing of these serotypes, Poutanen noted that 21 of 45 were clonal complex 320, which was not seen in the isolates before routine vaccine use. The researchers looked at four of 20 isolates collected before routine use of the vaccine.
She also noted this clonal type was more frequent than the 199, noted in the ABC Surveillance data, which she said warranted further study.