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Mastoiditis Caused by Pneumococcus Serotype 19A

In Houston, overall incidence of pneumococcal mastoiditis appears to be increasing; since the introduction of PCV7, nonvaccine serotype 19A has replaced vaccine serotypes.

Previously, researchers reported the emergence of Streptococcus pneumoniae (Sp) serotype 19A, which is multidrug-resistant and not included in the 7-valent pneumococcal conjugate vaccine (PCV7) (JW Infect Dis Nov 7 2007). These reports involved a variety of infections caused by an apparent clone of Sp. Now, in a study partially funded by PCV7’s manufacturer, investigators have linked this serotype to an increasing incidence of pneumococcal mastoiditis in children.

A chart review of patients admitted to Texas Children’s Hospital in Houston revealed 41 cases of new-onset acute pneumococcal mastoiditis between January 1995 and June 2007. Eighty-five percent of the children were aged <2 years. The most common serotype was 19A (46%). Serotype 19A infections involved more-serious disease than did non-19A infections: Significantly more children with 19A infections presented with subperiosteal abscesses (100% vs. 21%) and required mastoidectomy (89% vs. 45%).

The first case of Sp 19A mastoiditis occurred in 2003 (1 of 2 pneumococcal mastoiditis cases that year). Serotype 19A caused all six pneumococcal mastoiditis cases identified in 2006 and all nine in 2007. Pulsed-field gel electrophoresis showed that 14 of the 19 Sp 19A isolates tested (74%) belonged to a highly related group; 8 of these were indistinguishable. All 14 were highly resistant to penicillin, and most were resistant to multiple antibiotics.

Comment: Sp is the most common cause of mastoiditis in children. PCV7 contains 19F (but not 19A) polysaccharide. Recent data now demonstrate that the potential cross- protection against 19A by 19F has not been realized, and 19A infections have emerged in many U.S. states. This report emphasizes the importance of replacement of vaccine serotypes by serotype 19A, a highly virulent, multidrug-resistant pathogen.

— Robert S. Baltimore, MD

Published in Journal Watch Infectious Diseases July 9, 2008

Citation(s):

Ongkasuwan J et al. Pneumococcal mastoiditis in children and the emergence of multidrug-resistant serotype 19A isolates. Pediatrics 2008 Jul; 122:34.

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