Epidemiology and Infection

Improving sensitivity of oral fluid testing in IgG prevalence studies: application of mixture models to a rubella antibody survey

N. J. GAY a1c1, A. J. VYSE a1, F. ENQUSELASSIE a2, W. NIGATU a3 and D. J. NOKES a4p1
a1 Immunisation Division, PHLS Communicable Disease Surveillance Centre, 61 Colindale Avenue, London NW9 5EQ, UK
a2 Department of Community Health, Faculty of Medicine, University of Addis Ababa, Addis Ababa, Ethiopia
a3 Department of Infectious and Other Disease Research, Ethiopian Health and Nutrition Research Institute, Addis Ababa, Ethiopia
a4 Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK


A method for the analysis of age-stratified antibody prevalence surveys is applied to a previously reported survey of antibody to rubella virus using oral fluid samples in which the sensitivity of the assay used was shown to be compromised. The age-specific distribution of the quantitative results of antibody tests using oral fluids is modelled as a mixture of strong positive, weak positive and negative components. This yields maximum likelihood estimates of the prevalence at each age and demonstrates that, when used in conjunction with mixture modelling techniques, the results of antibody prevalence studies using oral fluids accurately reflect those obtained using sera.

(Accepted October 19 2002)

c1 Author for correspondence: CDSC, 61 Colindale Avenue, London NW9 5EQ, UK.
p1 Present address: Wellcome Trust Research Labs, Kenya Units, PO Box 230, Kilifi, Kenya.