title: Seroprevalence of pertussis in the Gambia: evidence for continued circulation of bordetella pertussis despite high vaccination rates.
abstract: BACKGROUND
  Bordetella pertussis can cause severe respiratory disease and death in children. In recent years, large outbreaks have occurred in high-income countries; however, little is known about pertussis incidence in sub-Saharan Africa.
  
  
  METHODS
  We evaluated antibody responses to pertussis toxin (Ptx) from individuals aged between 2 and 90 years in rural Gambia. IgG-Ptx was measured using luminex xMAP technology. IgG-Ptx geometric mean concentrations (GMC) and their 95% confidence intervals were calculated. The proportion seropositive (>20 EU/mL or ≥62.5 EU/mL) and GMCs were compared by age, sex, ethnic group, vaccination status, birth order and number of siblings per household using logistic and linear regression.
  
  
  RESULTS
  76.3% had anti-Ptx levels <20 EU/mL, 17.5% had concentrations between 20 and 62.5 EU/mL, 4.4% had concentrations between 62.5 and 125 EU/mL and 1.8% had concentrations ≥125 EU/mL. The overall Ptx antibody GMC was 6.4 EU/mL (95% confidence interval: 5.8-6.9). Higher antibody concentrations were observed in older populations with evidence for an increase in infection risk with increasing age (1.9% yearly increase, 95% confidence interval: 1.3-2.5). No child under 6 years of age had GMC above 62.5 EU/mL but 29.5% had concentrations between 20 and 62.5 EU/mL.
  
  
  CONCLUSIONS
  These data provide evidence that B. pertussis is being transmitted within this population despite high vaccination coverage. Re-infection may occur implying that immunity from childhood vaccination may not be lifelong. In the absence of data on actual clinical cases of pertussis, seroprevalence studies remain valuable tools to assess the transmission dynamics of B. pertussis.
authors.affiliation: From the *Medical Research Council (MRC) Unit, The Gambia, Fajara, The Gambia, West Africa; †Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, London, United Kingdom; ‡National Institute of Public Health and the Environment (RIVM), Centre for Infectious Diseases Control (CIb), Bilthoven, The Netherlands; §Julius Centre for Health Sciences and Primary Care, Utrecht University, Utrecht, The Netherlands; ¶International Agency for Research on Cancer, Lyon, France; and ‖Department of Paediatrics, Imperial College, London, United Kingdom.
authors.forename: Susana
authors.initials: S
authors.lastname: Scott
authors.forename: Marianne
authors.initials: M
authors.lastname: van der Sande
authors.forename: Tisbeh
authors.initials: T
authors.lastname: Faye-Joof
authors.forename: Maimuna
authors.initials: M
authors.lastname: Mendy
authors.forename: Bakary
authors.initials: B
authors.lastname: Sanneh
authors.forename: Fatou
authors.initials: F
authors.lastname: Barry Jallow
authors.forename: Hester
authors.initials: H
authors.lastname: de Melker
authors.forename: Fiona
authors.initials: F
authors.lastname: van der Klis
authors.forename: Pieter
authors.initials: P
authors.lastname: van Gageldonk
authors.forename: Frits
authors.initials: F
authors.lastname: Mooi
authors.forename: Beate
authors.initials: B
authors.lastname: Kampmann
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000907:Antibodies, Bacterial / Q000097:blood*; D000992:Antitoxins / Q000097:blood*; D001886:Bordetella pertussis; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D005714:Gambia / Q000453:epidemiology; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D015994:Incidence; D008297:Male; D008875:Middle Aged; D037342:Pertussis Toxin / Q000276:immunology; D011446:Prospective Studies; D016036:Seroepidemiologic Studies; D014917:Whooping Cough / Q000453:epidemiology*; D055815:Young Adult
chemical_list: D000907:Antibodies, Bacterial; D000992:Antitoxins; D007074:Immunoglobulin G; D037342:Pertussis Toxin