title: Changing trends in serotypes of S. pneumoniae isolates causing invasive and non-invasive diseases in unvaccinated population in Mexico (2000-2014).
abstract: OBJECTIVE
  Introduction of pneumococcal conjugate vaccines (PCV) targeted against a limited number of serotypes substantially decreased invasive (IPD) and non-invasive pneumococcal diseases (NIPD) but it was accompanied by non-vaccine type replacement disease. After 9 years of introduction of PCV in Mexico, we analyze the evidence of the indirect effects on IPD and NIPD serotype distribution among groups not targeted to receive the vaccine.
  
  
  METHODS
  From January 2000 to December 2014, pneumococcal strains isolated from IPD and NIPD cases from patients ≥5 years of age from participant hospitals of the SIREVA II (Sistema Regional de Vacunas) network were serotyped. A regression analysis was performed considering year and proportion of serotypes included in the different vaccine formulations (PCV7, PCV10 and PCV13). The slope was obtained for each regression line and their correspondent p-value. The proportion of each serotype in the pre-PCV7 and post-PCV7 periods was evaluated by χ2 test.
  
  
  RESULTS
  From a total of 1147 pneumococcal strains recovered, 570 corresponded to the pre-PCV7 and 577 to the post-PCV7 periods. The proportion of vaccine serotypes included in the three PCV formulations decreased by 2.4, 2.6 and 1.3%, respectively per year during the study period. A significant increase of serotype 19A was observed in the post-vaccine period in all age groups.
  
  
  CONCLUSIONS
  A percentage of annual decline of serotypes causing IPD and NIPD included in PCV was detected among groups not targeted to receive the vaccine, probably due to herd effect. Considering pneumococcal serotype distribution is a dynamic process, we highlight the importance of surveillance programs.
authors.affiliation: Instituto Nacional de Salud Pública, Av. Universidad 655, Cuernavaca, Morelos 62100, Mexico.
authors.forename: María Noemí
authors.initials: MN
authors.lastname: Carnalla-Barajas
authors.affiliation: Instituto Nacional de Salud Pública, Av. Universidad 655, Cuernavaca, Morelos 62100, Mexico.
authors.forename: Araceli
authors.initials: A
authors.lastname: Soto-Noguerón
authors.affiliation: Instituto Nacional de Salud Pública, Av. Universidad 655, Cuernavaca, Morelos 62100, Mexico.
authors.forename: Miguel Angel
authors.initials: MA
authors.lastname: Sánchez-Alemán
authors.affiliation: Unidad Médica de Alta Especialidad, Hospital de Pediatría Centro Médico Nacional SXXI, Instituto Mexicano del Seguro Social, Av. Cuauhtemoc 330, Col. Doctores, CP 06720 Mexico City.
authors.forename: Fortino
authors.initials: F
authors.lastname: Solórzano-Santos
authors.affiliation: Instituto Nacional de Salud Pública, Av. Universidad 655, Cuernavaca, Morelos 62100, Mexico.
authors.forename: María Elena
authors.initials: ME
authors.lastname: Velazquez-Meza
authors.affiliation: Instituto Nacional de Salud Pública, Av. Universidad 655, Cuernavaca, Morelos 62100, Mexico. Electronic address: igechaniz@insp.mx.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Echániz-Aviles
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D006761:Hospitals; D006801:Humans; D008297:Male; D008800:Mexico; D008875:Middle Aged; D011008:Pneumococcal Infections / Q000382:microbiology*; D022242:Pneumococcal Vaccines / Q000008:administration & dosage; D012703:Serotyping; D013296:Streptococcus pneumoniae / Q000145:classification* / Q000302:isolation & purification; D018074:Vaccines, Conjugate / Q000008:administration & dosage; D055815:Young Adult
chemical_list: D022242:Pneumococcal Vaccines; D018074:Vaccines, Conjugate
keywords: Mexico; S. pneumoniae; herd effect; pneumococcal conjugate vaccine; serotype distribution