title: Markov model to forecast the change in prevalence of soil-transmitted helminths during a control programme: a case study in Vietnam.
abstract: BACKGROUND
  A mathematical model based on the Markov methodology to predict the change in prevalence of soil-transmitted helminth (STH) infections during public health control activities is not available, but would be an extremely efficient planning tool.
  
  
  METHODS
  We used the parasitological data collected during a deworming and iron supplementation programme for women of child-bearing age conducted in Vietnam between 2006 and 2011 to develop a Markov transition probability model. The transition probabilities were calculated from the observed changes in prevalence in the different classes of intensity for each STH species during the first year of intervention. The model was then developed and used to estimate the prevalence in year 2, 3, 4 and 5 for each STH species and for 'any STH infection'. The prevalence predicted by the model was then compared with the prevalence observed at different times during programme implementation.
  
  
  RESULTS
  The comparison between the model-predicted prevalence and the observed prevalence proved a good fit of the model.
  
  
  CONCLUSIONS
  We consider the Markov transition probability model to be a promising method of predicting changes in STH prevalence during control efforts. Further research to validate the model with observed data in different geographical and epidemiological settings is suggested to refine the prediction model.
authors.affiliation: Department of Control of Neglected Tropical Diseases, World Heath Organization, Avenue Appia 20, 1211 Geneva, Switzerland. montresora@who.int
authors.forename: Antonio
authors.initials: A
authors.lastname: Montresor
authors.forename: Albis Francesco
authors.initials: AF
authors.lastname: Gabrielli
authors.forename: Aya
authors.initials: A
authors.lastname: Yajima
authors.forename: Nam
authors.initials: N
authors.lastname: Lethanh
authors.forename: Beverley-Ann
authors.initials: BA
authors.lastname: Biggs
authors.forename: Gerald J
authors.initials: GJ
authors.lastname: Casey
authors.forename: Ta Thi
authors.initials: TT
authors.lastname: Tinh
authors.forename: Dirk
authors.initials: D
authors.lastname: Engels
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Savioli
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D005260:Female; D005544:Forecasting; D006373:Helminthiasis / Q000453:epidemiology* / Q000469:parasitology / Q000635:transmission; D006376:Helminths / Q000469:parasitology*; D006801:Humans; D008137:Longitudinal Studies; D008390:Markov Chains; D008875:Middle Aged; D015995:Prevalence; D012987:Soil / Q000469:parasitology*; D012988:Soil Microbiology; D014744:Vietnam; D055815:Young Adult
chemical_list: D012987:Soil