title: Assessing the impact of misclassification error on an epidemiological association between two helminthic infections.
abstract: BACKGROUND
  Polyparasitism can lead to severe disability in endemic populations. Yet, the association between soil-transmitted helminth (STH) and the cumulative incidence of Schistosoma japonicum infection has not been described. The aim of this work was to quantify the effect of misclassification error, which occurs when less than 100% accurate tests are used, in STH and S. japonicum infection status on the estimation of this association.
  
  
  RESULTS
  Longitudinal data from 2276 participants in 50 villages in Samar province, Philippines treated at baseline for S. japonicum infection and followed for one year, served as the basis for this analysis. Participants provided 1-3 stool samples at baseline and 12 months later (2004-2005) to detect infections with STH and S. japonicum using the Kato-Katz technique. Variation from day-to-day in the excretion of eggs in feces introduces individual variations in the sensitivity and specificity of the Kato-Katz to detect infection. Bayesian logit models were used to take this variation into account and to investigate the impact of misclassification error on the association between these infections. Uniform priors for sensitivity and specificity of the diagnostic test to detect the three STH and S. japonicum were used. All results were adjusted for age, sex, occupation, and village-level clustering. Without correction for misclassification error, the odds ratios (ORs) between hookworm, Ascaris lumbricoides, and Trichuris trichiura, and S. japonicum infections were 1.28 (95% Bayesian credible intervals: 0.93, 1.76), 0.91 (95% BCI: 0.66, 1.26), and 1.11 (95% BCI: 0.80, 1.55), respectively, and 2.13 (95% BCI: 1.16, 4.08), 0.74 (95% BCI: 0.43, 1.25), and 1.32 (95% BCI: 0.80, 2.27), respectively, after correction for misclassification error for both exposure and outcome.
  
  
  CONCLUSIONS
  The misclassification bias increased with decreasing test accuracy. Hookworm infection was found to be associated with increased 12-month cumulative incidence of S. japonicum infection after correction for misclassification error. Such important associations might be missed in analyses which do not adjust for misclassification errors.
authors.affiliation: Department of Biostatistics and Epidemiology, College of Public Health, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States of America. mtarafder@tcmedc.org
authors.forename: Mushfiqur R
authors.initials: MR
authors.lastname: Tarafder
authors.forename: Hélène
authors.initials: H
authors.lastname: Carabin
authors.forename: Stephen T
authors.initials: ST
authors.lastname: McGarvey
authors.forename: Lawrence
authors.initials: L
authors.lastname: Joseph
authors.forename: Ernesto
authors.initials: E
authors.lastname: Balolong
authors.forename: Remigio
authors.initials: R
authors.lastname: Olveda
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D000871:Anthelmintics / Q000008:administration & dosage; D017164:Ascaris lumbricoides / Q000302:isolation & purification; D002648:Child; D002675:Child, Preschool; D015897:Comorbidity; D003951:Diagnostic Errors; D005243:Feces / Q000469:parasitology; D005260:Female; D006373:Helminthiasis / Q000188:drug therapy / Q000453:epidemiology*; D006376:Helminths / Q000145:classification* / Q000302:isolation & purification*; D006801:Humans; D015994:Incidence; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D010274:Parasitology / Q000379:methods; D010679:Philippines / Q000453:epidemiology; D012549:Schistosoma japonicum / Q000302:isolation & purification; D014258:Trichuris / Q000302:isolation & purification; D055815:Young Adult
chemical_list: D000871:Anthelmintics