The effect of participant non-response on the HIV prevalence estimates in a population based survey in two informal settlements in Nairobi city

Background:Participant non-response in an HIV sero-survey can affect estimates of HIV prevalence. Non-response can arise from refusals to provide a blood sample or failure to trace a sampled individual. In a sero-survey conducted by the African Population and Health Research Center and Kenya Medical Research Centre in the slums of Nairobi, 46% of the sampled individuals did not provide a blood sample. This paper describes selective participation in the sero-survey and also estimates bias in HIV prevalence figures.Methods:The paper uses data derived from an HIV sero-survey nested in an ongoing demographic surveillance system. Non-response was assessed using logistic regression and multiple imputation methods to impute missing data for HIV status using a set of common variables available for all sampled participants.Results:Age, residence, high mobility, wealth and ethnicity were independent predictors of a sampled individual not being contacted. Individuals aged 30-34 years, females, individuals from the Kikuyu and Kamba ethnicity, the married and residents of Viwandani were all less likely to accept to be tested. Although men were less likely to be contacted, those found were more willing to be tested compared to females. The overall observed HIV prevalence was overestimated by 2%. The observed prevalence for male participants was underestimated by about 2% and that for females was overestimated by 4%. These differences were small and did not affect the overall estimate substantially as the observed estimates fell within the confidence limits of the corrected prevalence estimate. Conclusions:Non-response to HIV sero-survey in informal settlements is high. The effect on the overall prevalence estimate was however minimal.