Last Updated: 2007-10-19 14:28:48 -0400 (Reuters Health)

NEW YORK (Reuters Health) – From 2001 to 2006, a marked increase in serotype 19A Streptococcus pneumoniae, which is often resistant to multiple antibiotics, occurred in Massachusetts, researchers note in the October 19th issue of the Morbidity and Mortality Weekly Report.

By contrast, the overall rates of invasive pneumococcal disease held steady during the study period. At the same time, a drop occurred in antibiotic-resistant cases covered by the heptavalent pneumococcal conjugate vaccine (PCV7), which was introduced across the US in 2000. Serotype 19A is not covered by the vaccine.

The Massachusetts Department of Public Health in collaboration with Boston University began statewide surveillance for invasive pneumococcal disease among children beginning in October 2001. Estimates suggest that by 2005, nearly 95% of young children in the state had received three or more doses of PCV7.

During the study period, annual invasive pneumococcal disease rates were generally stable, ranging from 15.9 to 18.6 cases per 100,000 children younger than 5 years. These rates are 70% lower than those seen before the PCV7 vaccination program was introduced.

Invasive pneumococcal disease due to serotype 19A was uncommon. However, from 2001 to 2006, the percentage of all cases caused by this species rose from 10% to 41% (p < 0.01). By contrast, the contribution made by other types to the overall burden of invasive pneumococcal disease did not change significantly.

Susceptibility testing showed that the 19A isolates developed greater antibiotic resistance over time. Specifically, in 2001-2002, 0% of 19A isolates were resistant to three or more antibiotic classes compared with 42% of isolates in 2005-2006 (p < 0.05).

"Continued surveillance for invasive pneumococcal disease in Massachusetts will provide data on the clinical impact of antimicrobial-nonsusceptible 19A infection and will be useful in development and monitoring of new pneumococcal vaccines," the report concludes.

Mor Mortal Wkly Rep CDC Surveill Summ 2007;56:1077-1080.