Streptococcus pneumoniae Serotypes Identified in Mexican Children with Invasive Disease Before and After the Introduction of PCV7 (1993-2012)

Abstract

Background and aims: Streptococcus pneumoniae is the leading cause of acute otitis media, pneumonia, meningitis, and sepsis. The heptavalent pneumococcal conjugate vaccine (PCV7) was incorporated into the national immunization program in Mexico in 2008. The aim of the study was to analyze the frequency of S. pneumoniae serotypes isolated from children ≤5 years of age with invasive diseases before and after the introduction of PCV7.

Methods: Isolates from sterile fluids, tissues and other body fluids were obtained from 1993 to 2012. Isolates collected in hospitals for the surveillance network were sent to the Instituto Nacional de Salud Publica. Serotyping was done using the Quellung reaction. The pre-vaccination period was considered from 1993-2007.

Results: A total of 1346 isolates were collected during 1993-2012. In the pre-vaccination era, serotypes included in PCV7 accounted for 59.7% of the strains, whereas in 2012 they represented only 21% of cases. There was a significant decrease in all PCV7-included serotypes. A gradual increase of the 19A serotype was detected during the vaccination period from 7% in 2008 to 39% of the isolates in 2012. In this year, 29% of the serotypes causing invasive disease were not included in any of the pneumococcal conjugate vaccines.

Conclusion: The emergence of PCV7 non-included serotypes after vaccination demands increased surveillance. Currently in Mexico, the 13-valent conjugate vaccine (PCV13) offers better coverage than the 10-valent pneumococcal conjugate vaccine (PCV10).

Keywords: Children; Immunization program; Mexico; Pneumococcal vaccine; Streptococcus pneumoniae.