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Serotype 19A S. pneumoniae: A Growing Problem for Children

Serotype 19A pneumococcal strains have emerged in New York and Massachusetts, causing otitis and invasive pneumococcal disease in children.

Introduction of heptavalent pneumococcal conjugate vaccine (PCV7) in the U.S. in 2000 was followed by a reduction in the rate of invasive pneumococcal disease (IPD) among young children (see Journal Watch Infectious Diseases May 23 2003). The seven serotypes contained in this vaccine are estimated to cause 80% to 85% of IPD cases in children. Recently, type 19A (which is not included in PVC7) has emerged among Alaska Native children, causing an increase in IPD rates in this population (see Journal Watch Infectious Diseases May 2 2007). Two recent reports alert us to the growing threat from Streptococcus pneumoniae type 19A in the continental U.S.

Pichichero and Casey, in work partially supported by industry, have been monitoring otopathogens in selected children in Rochester, New York. From September 2003 through June 2006, they performed tympanocentesis on 212 children who were experiencing their first or second episode of acute otitis media (AOM), recurrent AOM, or AOM treatment failure with first-line antibiotics. S. pneumoniae was isolated from middle ear fluid samples from 59 children. Twenty-five isolates were PCV7 serotypes, and 34 were non-PCV7 serotypes (of which 9 were 19A). During the study period, the proportion of PCV7 serotypes among the S. pneumoniae isolates decreased significantly, whereas the proportion of non-PCV7 serotypes increased significantly. The nine 19A isolates were resistant to all antibiotics approved by the FDA for treating children with AOM; on multilocus sequence typing, all nine isolates appeared to be the same clone. Four of the children from whom this strain was isolated were treated by insertion of tympanostomy tubes; the other five were treated successfully with levofloxacin, a fluoroquinolone antibiotic not currently approved for treating children with AOM.

The CDC reported data from statewide laboratory- and population-based surveillance for IPD among Massachusetts children from October 2001 through September 2006. Previous investigations had shown that, following the introduction of PCV7, the rate of IPD fell by approximately 70% among children aged <5 years. In the present study, the annual rate was steady from 2001 through 2006 among children aged <5 years as well as among those aged 5 to 17 years. Of 467 IPV cases reported during this period, isolates from 353 were serotyped. The most common serotype was 19A; the proportion of cases caused by this serotype increased each year during the surveillance period, from 10% in 2001–2002 to 41% in 2005–2006. Most 19A isolates were not susceptible to penicillin. During the study period, significant increases were noted in the proportions of 19A isolates that were not susceptible to amoxicillin or were not susceptible to 3 antimicrobial classes.

Comment: These reports are both interesting and alarming. When PCV7 was introduced, researchers assumed that serotype 19F (which is contained in PCV7) would protect against the related 19A. This assumption been proven untrue; in addition, numerous reports have shown that 19A has become a replacement strain that causes significant problems in diverse populations. If the clone of 19A identified in Rochester is similar or identical to the isolates in Massachusetts, we have reason to be concerned about the emergence of a "superbug" that could cause IPD. A new pneumococcal conjugate vaccine with coverage expanded to include serotype 19A is clearly needed.

— Robert S. Baltimore, MD

Published in Journal Watch Infectious Diseases November 7, 2007

Citation(s):

Pichichero ME and Casey JR. Emergence of a multiresistant serotype 19A pneumococcal strain not included in the 7-valent conjugate vaccine as an otopathogen in children. JAMA 2007 Oct 17; 298:1772.

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• Medline abstract (Free)

Centers for Disease Control and Prevention (CDC). Emergence of antimicrobial-resistant serotype 19A Streptococcus pneumoniae — Massachusetts, 2001–2006. MMWR Morb Mortal Wkly Rep 2007 Oct 19; 56:1077.

• Medline abstract (Free)