title: Norovirus Infection and Acquired Immunity in 8 Countries: Results From the MAL-ED Study.
abstract: Norovirus is an important cause of childhood diarrhea. We present data from a longitudinal, multicountry study describing norovirus epidemiology during the first 2 years of life.
  
  
  
  A birth cohort of 1457 children across 8 countries contributed 7077 diarrheal stools for norovirus testing. A subset of 199 children contributed additional asymptomatic samples (2307) and diarrheal stools (770), which were used to derive incidence rates and evaluate evidence for acquired immunity.
  
  
  
  Across sites, 89% of children experienced at least 1 norovirus infection before 24 months, and 22.7% of all diarrheal stools were norovirus positive. Severity of norovirus-positive diarrhea was comparable to other enteropathogens, with the exception of rotavirus. Incidence of genogroup II (GII) infection was higher than genogroup I and peaked at 6-11 months across sites. Undernutrition was a risk factor for symptomatic norovirus infection, with an increase in 1 standard deviation of length-for-age z score associated with a 17% reduction (odds ratio, 0.83 [95% confidence interval, .72-.97]; P = .011) in the odds of experiencing diarrhea when norovirus was present, after accounting for genogroup, rotavirus vaccine, and age. Evidence of acquired immunity was observed among GII infections only: Children with prior GII infection were found to have a 27% reduction in the hazard of subsequent infection (hazard ratio, 0.727; P = .010).
  
  
  
  The high prevalence of norovirus across 8 sites in highly variable epidemiologic settings and demonstration of protective immunity for GII infections provide support for investment in vaccine development.
authors.affiliation: Johns Hopkins School of Public Health.
authors.forename: Saba
authors.initials: S
authors.lastname: Rouhani
authors.affiliation: Johns Hopkins University, Baltimore, Maryland.
authors.forename: Pablo
authors.initials: P
authors.lastname: Peñataro Yori
authors.affiliation: A.B. PRISMA, Iquitos, Peru.
authors.forename: Maribel
authors.initials: M
authors.lastname: Paredes Olortegui
authors.affiliation: A.B. PRISMA, Iquitos, Peru.
authors.forename: Mery
authors.initials: M
authors.lastname: Siguas Salas
authors.affiliation: A.B. PRISMA, Iquitos, Peru.
authors.forename: Dixner
authors.initials: D
authors.lastname: Rengifo Trigoso
authors.affiliation: International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b), Dhaka.
authors.forename: Dinesh
authors.initials: D
authors.lastname: Mondal
authors.affiliation: Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand.
authors.forename: Ladaporn
authors.initials: L
authors.lastname: Bodhidatta
authors.affiliation: University of Virginia, Charlottesville.
authors.forename: James
authors.initials: J
authors.lastname: Platts-Mills
authors.affiliation: University of Venda, Thohoyandou, South Africa.
authors.forename: Amidou
authors.initials: A
authors.lastname: Samie
authors.affiliation: Aga Khan University, Naushahro Feroze, Pakistan.
authors.forename: Furqan
authors.initials: F
authors.lastname: Kabir
authors.affiliation: Universidade Federal do Ceará, Fortaleza, Brazil.
authors.forename: Aldo
authors.initials: A
authors.lastname: Lima
authors.affiliation: Christian Medical College, Vellore, India.
authors.forename: Sudhir
authors.initials: S
authors.lastname: Babji
authors.affiliation: Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand.
authors.forename: Carl J
authors.initials: CJ
authors.lastname: Mason
authors.affiliation: Aga Khan University, Naushahro Feroze, Pakistan.
authors.forename: Adil
authors.initials: A
authors.lastname: Kalam
authors.affiliation: Aga Khan University, Naushahro Feroze, Pakistan.
authors.forename: Pascal
authors.initials: P
authors.lastname: Bessong
authors.affiliation: International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b), Dhaka.
authors.forename: Tahmeed
authors.initials: T
authors.lastname: Ahmed
authors.affiliation: Haydom Lutheran Hospital, Haydom, Tanzania.
authors.forename: Estomih
authors.initials: E
authors.lastname: Mduma
authors.affiliation: Aga Khan University, Naushahro Feroze, Pakistan.
authors.forename: Zulfiqar A
authors.initials: ZA
authors.lastname: Bhutta
authors.affiliation: Universidade Federal do Ceará, Fortaleza, Brazil.
authors.forename: Ila
authors.initials: I
authors.lastname: Lima
authors.affiliation: Christian Medical College, Vellore, India.
authors.forename: Rakhi
authors.initials: R
authors.lastname: Ramdass
authors.affiliation: Foundation for the National Institutes of Health, Bethesda, Maryland.
authors.forename: Dennis
authors.initials: D
authors.lastname: Lang
authors.affiliation: Christian Medical College, Vellore, India.
authors.forename: Ajila
authors.initials: A
authors.lastname: George
authors.affiliation: Aga Khan University, Naushahro Feroze, Pakistan.
authors.forename: Anita K M
authors.initials: AK
authors.lastname: Zaidi
authors.affiliation: Christian Medical College, Vellore, India.
authors.forename: Gagandeep
authors.initials: G
authors.lastname: Kang
authors.affiliation: University of Virginia, Charlottesville.
authors.forename: Eric
authors.initials: E
authors.lastname: Houpt
authors.affiliation: Johns Hopkins School of Public Health.
authors.forename: Margaret N
authors.initials: MN
authors.lastname: Kosek
mesh_terms: D017250:Caliciviridae Infections / Q000453:epidemiology / Q000276:immunology / Q000821:virology; D002675:Child, Preschool; D015331:Cohort Studies; D003967:Diarrhea / Q000453:epidemiology / Q000276:immunology / Q000821:virology; D005243:Feces / Q000821:virology; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D029322:Norovirus / Q000235:genetics*
keywords: diarrhea; immunity; norovirus