title: Nutrition surveillance using a small open cohort: experience from Burkina Faso.
abstract: BACKGROUND
  Nutritional surveillance remains generally weak and early warning systems are needed in areas with high burden of acute under-nutrition. In order to enhance insight into nutritional surveillance, a community-based sentinel sites approach, known as the Listening Posts (LP) Project, was piloted in Burkina Faso by Action Contre la Faim (ACF). This paper presents ACF's experience with the LP approach and investigates potential selection and observational biases.
  
  
  METHODS
  Six primary sampling units (PSUs) were selected in each livelihood zone using the centric systematic area sampling methodology. In each PSU, 22 children aged between 6 and 24 months were selected by proximity sampling. The prevalence of GAM for each month from January 2011 to December 2013 was estimated using a Bayesian normal-normal conjugate analysis followed by PROBIT estimation. To validate the LP approach in detecting changes over time, the time trends of MUAC from LP and from five cross-sectional surveys were modelled using polynomial regression and compared by using a Wald test. The differences between prevalence estimates from the two data sources were used to assess selection and observational biases.
  
  
  RESULTS
  The 95 % credible interval around GAM prevalence estimates using LP approach ranged between +6.5 %/-6.0 % on a prevalence of 36.1 % and +3.5 %/-2.9 % on a prevalence of 10.8 %. LP and cross-sectional surveys time trend models were well correlated (p = 0.6337). Although LP showed a slight but significant trend for GAM to decrease over time at a rate of -0.26 %/visit, the prevalence estimates from the two data sources showed good agreement over a 3-year period.
  
  
  CONCLUSIONS
  The LP methodology has proved to be valid in following trends of GAM prevalence for a period of 3 years without selection bias. However, a slight observational bias was observed, requiring a periodical reselection of the sentinel sites. This kind of surveillance project is suited to use in areas with high burden of acute under-nutrition where early warning systems are strongly needed. Advocacy is necessary to develop sustainable nutrition surveillance system and to support the use of surveillance data in guiding nutritional programs.
authors.affiliation: Action Contre la Faim, 16 Boulevard Douaumont, 75017 Paris, France.
authors.forename: Mathias
authors.initials: M
authors.lastname: Altmann
authors.affiliation: EHESP Sorbonne Paris Cité, Avenue du Professeur Léon-Bernard, 35043 Rennes, France.
authors.forename: Christophe
authors.initials: C
authors.lastname: Fermanian
authors.affiliation: Ecole des Hautes Etudes en Santé Publique, Avenue du Professeur Léon-Bernard, 35043 Rennes, France.
authors.forename: Boshen
authors.initials: B
authors.lastname: Jiao
authors.affiliation: Action Contre la Faim, 16 Boulevard Douaumont, 75017 Paris, France.
authors.forename: Chiara
authors.initials: C
authors.lastname: Altare
authors.affiliation: Action Contre la Faim, Ouagadougou, Burkina Faso.
authors.forename: Martin
authors.initials: M
authors.lastname: Loada
authors.affiliation: Brixton Heath, Llawryglyn, Powys, Wales UK.
authors.forename: Mark
authors.initials: M
authors.lastname: Myatt
keywords: Burkina Faso; Humanitarian; Nutrition; Observational bias; Selection bias; Surveillance