title: Real-time Polymerase Chain Reaction Analysis of Sewage Samples to Determine Oral Polio Vaccine Circulation Duration and Mutation After Mexican National Immunization Weeks.
abstract: BACKGROUND
  Oral polio vaccine (OPV) can mutate and cause outbreaks of paralytic poliomyelitis with prolonged replication. After poliovirus eradication, global use of inactivated polio vaccine (IPV) may be needed until all OPV stops circulating. Mexico, where children receive routine IPV but where OPV is given only during biannual national immunization weeks (NIWs), provides a natural setting to study duration of OPV circulation in a community primarily vaccinated with IPV.
  
  
  METHODS
  One-liter sewage samples from four separate arroyos (creeks) near Orizaba, Mexico, were collected monthly for 12 months. Concentrated sewage underwent RNA extraction, reverse transcription, and real-time polymerase chain reaction (PCR) to detect OPV serotypes 1, 2, and 3 and their variants containing the serotype-specific point mutation in the 5' untranslated region associated with neurovirulence.
  
  
  RESULTS
  OPV was detected 3, 4, 5, and 7 months after the May 2010 NIW, but was not detected at 6 or 8 months. A second and third NIW occurred in February 2011 and May 2011, and OPV was detected in the sewage monthly after both of these NIW through July 2011 when collection stopped. The OPV detected was primarily serotype 2 and predominantly contained the point mutations in the 5' untranslated region associated with increased neurovirulence.
  
  
  CONCLUSIONS
  OPV was detected in sewage as late as 7 months after an NIW in a Mexican community primarily vaccinated with IPV, but was not detected at 8 months, suggesting that OPV circulation may have ceased. These data suggest that in communities with high vaccination rates, 1 or 2 years of IPV administration after OPV cessation could be sufficient to prevent outbreaks of paralytic poliomyelitis from vaccine-derived strains.
authors.affiliation: Stanford University School of Medicine, California Eastern Virginia Medical School, Norfolk.
authors.forename: Stephanie B
authors.initials: SB
authors.lastname: Troy
authors.affiliation: Instituto Nacional de Salud Pública, Cuernavaca, Morelos, Mexico.
authors.forename: Leticia
authors.initials: L
authors.lastname: Ferreyra-Reyes
authors.affiliation: Instituto Nacional de Salud Pública, Cuernavaca, Morelos, Mexico.
authors.forename: Sergio
authors.initials: S
authors.lastname: Canizales-Quintero
authors.affiliation: Stanford University School of Medicine, California.
authors.forename: ChunHong
authors.initials: C
authors.lastname: Huang
authors.affiliation: Stanford University School of Medicine, California.
authors.forename: Yu-Jin
authors.initials: YJ
authors.lastname: Lee
authors.affiliation: Instituto Nacional de Salud Pública, Cuernavaca, Morelos, Mexico.
authors.forename: Renata
authors.initials: R
authors.lastname: Báez-Saldaña
authors.affiliation: Instituto Nacional de Salud Pública, Cuernavaca, Morelos, Mexico.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Ferreira-Guerrero
authors.affiliation: Instituto Nacional de Salud Pública, Cuernavaca, Morelos, Mexico.
authors.forename: Lourdes
authors.initials: L
authors.lastname: García-García
authors.affiliation: Stanford University School of Medicine, California.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Maldonado
keywords: Mexico; OPV; PCR; Polio; Sewage