ABSTRACT
<p><b>OBJECTIVE</b>To study the loss to follow-up (LTF) rate, HIV emerging incidence and influencing factors in the longitudinal study of female sex workers (FSWs) in Kaiyuan, Yunnan, and their influence on HIV emerging incidence estimate.</p><p><b>METHODS</b>The open cohort study on FSWs was launched in March 2006 and ended in June 2013 in Kaiyuan, Yunnan. Investigations were made every six months and lasted for 7 years. 661 FSWs found as HIV negative in the baseline study in March 2006 were chosen to study their LTF in the 7 year follow-up investigation. The Cox regression model was used to explore risk factors for HIV emerging infection and those for LTF. In June 2013, a survey was also conducted to explore the detailed reasons for loss to follow-up by contacting FSWs themselves.</p><p><b>RESULTS</b>During 1 238.5 person-years of follow-up among 661 HIV negative FSWs, the HIV incidence rate was 1.29 (95% CI: 0.74-2.10)/100 person-year, and the LFT incidence rate was 48.68 (95% CI: 44.88-52.73) /100 person-year. The multivariate analysis showed drug abuse as an independent risk factor for FSWs' infection of HIV (adjusted risk ratio = 4.15, 95% CI: 1.43-12.02); FSWs over 25 years old (adjusted risk ratio = 0.68, 95% CI: 0.57-0.81), and drug abuse (adjusted risk ratio = 0.52, 95% CI: 0.35-0.79) were found with lower LFT rate to remain in the cohort.</p><p><b>CONCLUSION</b>High LFT rate was found in FSW cohort study in Kaiyuan, Yunnan, while the HIV infection risk exposure of the LFT group was lower than the groups of HIV follow-up. HIV prevalence of FSWs in the city might be overestimated. Causes of LFT of FSWs group required further study in the future, and the cohort follow-up retention strategy for FSWs needs to be developed.</p>