Streptococcus pneumoniae 19A: An Emerging Threat

Since the licensure of the heptavalent pneumococcalconjugate vaccine (PCV7) in 2000, the prevalence ofinvasive pneumococcal disease (IPD) among childrenin the United States has decreased significantly. Theincidence of IPD caused by pneumococcal serotypes associatedwith PCV7 among children younger than 5 yearsdecreased from 80 cases per 100,000 population in 1998 to1999 to 4.6 cases per 100,000 population in 2003.¹ Variousstudies have demonstrated that nasopharyngeal colonizationwith pneumococcal serotypes covered by thevaccine also has decreased. However, several studies suggestthat in some settings, these bacterial populationshave been replaced with Streptococcus pneumoniae serotypesnot covered by the vaccine.^2,3

Among the various pneumococcal serotypes (19A, 6A,3, and 15) that have been recognized as emerging threatsduring recent years, S pneumoniae 19A is, by far, the mostprominent. This serotype has been associated not onlywith the development of IPD but also with a high levelof resistance to multiple antibiotic classes.^2,4,5

IPD surveillance in Massachusetts during 2001 to 2006identified a significant increase in cases caused by serotypesnot covered by the PCV7.² The percentage of infectionscaused by serotype 19A increased from 10% during2001 to 2003 to 41% during 2005 to 2006. In Alaska,serotype 19Awas the cause of 28.3% of cases of IPD amongchildren younger than 2 years between 2004 and 2006.³

In addition to IPD, multiresistant serotype 19Aalso hasbeen linked to the development of otitis media. As evidencedby Pichichero and Casey⁵ and by Jacobs and colleagues⁶in 2 separate studies, a significant challenge relatedto this clinical situation is the high level of resistancethat many of these isolates have to antibiotics (such asamoxicillin, trimethoprim, macrolides, clindamycin, oralcephalosporins, and ceftriaxone) most commonly used totreat otitis media in children.

The direct effect of PCV7 in serotype selection or replacementis not yet fully understood. Although serotypeselection induced by lack of effectiveness of PCV7 againstserotype 19A is believed to be 1 of the main factors associatedwith serotype 19A proliferation, it is not the onlyfactor. Moore and colleagues⁷ have suggested that antibioticresistance, clonal expansion, and capsular switchingalso have contributed to the emergence of this serotypeas the predominant cause of IPD in the United States. Inaddition, it is important to emphasize that according to arecent study by Hwa Choi and colleagues,⁸ multidrugresistant19A serotypes began to increase in South Koreabefore the introduction of PCV7.

The introduction and widespread administration ofPCV7 to children in the United States has led to a significantdecrease in the incidence of IPD. However, it isimportant for clinicians to recognize that because ofmultiple factors, multidrug-resistant serotype 19A hasemerged as a significant cause of pneumococcal disease.Clinicians need to consider the presence of this serotypein situations in which IPD is observed. In addition, infectionwith S pneumoniae 19A should be considered in childrenwith otitis media who fail to respond to antibiotictherapy.

References:

• Centers for Disease Control and Prevention. Direct and indirect effects of routine vaccination of children with 7-valent pneumococcal conjugate vaccine on incidence of invasive pneumococcal disease-United States, 1998-2003. MMWR. 2005;54:893-897.

•  Centers for Disease Control and Prevention. Emergence of antimicrobialresistant serotype 19A Streptococcus pneumoniae-Massachusetts, 2001-2006. MMWR. 2007;56:1077-1080.

•  Singleton RJ, Hennessy TW, Bulkow LR, et al. Invasive pneumococcal disease caused by nonvaccine serotypes among Alaska native children with high levels of 7-valent pneumo coccal conjugate vaccine coverage. JAMA. 2007;297:1784-1792.

•  Farrell DJ, Klugman KP, Pichichero M. Increased antimicrobial resistance among nonvaccine serotypes of Streptococcus pneumoniae in the pediatric population after the introduction of 7-valent pneumococcal vaccine in the United States. Pediatr Infect Dis J. 2007;26:123-128.

•  Pichichero ME, 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;298:1772-1778.

•  Jacobs MR, Good CE, Sellner T, et al. Nasopharyngeal carriage of respiratory pathogens in children undergoing pressure equalization tube placement in the era of pneumococcal protein conjugate vaccine use. Laryngoscope. 2007; 117:295-29

•  Moore MR, Gertz RE Jr, Woodbury RL, et al. Population snapshot of emergent Streptococcus pneumoniae serotype 19A in the United States, 2005. J Infect Dis. 2008;197:1016-1027.

• Hwa Choi E, Hee Kim S, Wook Eun B, et al. Streptococcus pneumoniae serotype 19A in children, South Korea. Emerg Infect Dis. 2008;14:275-281.