Dropouts in a long-term follow-up study involving voluntary counseling and HIV testing: Experience from a cohort of police officers in Dar Es Salaam, Tanzania

Background: Results of most population-based studies primarily are derived from people who responded positively and thereby continued to participate in such studies. It is, however, equally important to know the characteristics of study subjects who drop out to learn the reasons that kept them from continuing to participate in the study, especially because they had initially agreed to participate in such a study. In studies with long-term follow-up, reasons for nonresponse may provide invaluable information that may be gathered through continued contact with study subjects who have withdrawn from the study. Objectives: To determine characteristics of study participants who withdrew from an ongoing study of police officers, which involved counseling and HIV testing, and to determine reasons for their discontinued participation. Methods: Demographic characteristics of a cohort of police officers who had been participating in a study to determine their suitability for HIV vaccine trials were analyzed. Characteristics of those who did not return for the second survey of appointments for HIV testing were compared with those who continued their participation. A randomly selected sample of 132 police officers who did not participate in the second survey of HIV testing were asked why they did not return. Answers were obtained from 84 people who had discontinued their participation. Results: Of eligible police officers, 2087 (72.1%) responded to the call for follow-up appointments, whereas 807 (27.9%) did not return. Those who did not return to participate in the second survey had significantly higher rates of HIV seropositivity (17.2%) than those who did return (13.5%) (p <.05). The rate of return in unmarried participants was worse (p <.05) than the rate among married participants. Rates of sexual contacts with partners other than their spouses and levels of alcohol consumption did not differ between the two groups. Reasons for dropping out of the study included fear of knowing results of HIV testing in 54.6%, lack of time to continue in 34.5%, and fears about job security in 3.6%. Conclusion: Fears of finding out that one might be seropositive need to be answered at recruitment, and practical arrangements must be made to facilitate further follow-up. A bias for lower incidence might be introduced in vaccine trials if participants thought to be at highest risk for HIV infection discontinue participation.