| ObjectivesBehavioral interventions are effective strategies for HIV/AIDS prevention and control.However, implementation of such strategies relies heavily on the accurate estimationof the high-risk population size. Populations at high risk for humanimmunodeficiency virus mainly include female sex workers, men who have sex withmen, and injection drug users). These groups are considered as hidden orhard-to-reach populations with two characteristics that create difficulties forestimating population size:1) They tend to hide their true identities from the publicbecause of the stigma; and2) There is no sampling frame used for surveys. However,without reliable estimates of the size of these at-risk populations, the ability ofgovernments to carry out intervention planning, resource allocation, estimate thenumber of people infected with HIV, project disease burden, measure coverage, andevaluate interventions is limited. With these issues in mind, the Joint United NationsProgramme on HIV/AIDS and the World Health Organization released guidelines in2003, which were updated in2010, for estimating the size of populations at high riskfor HIV. The guideline encompasses enumeration methods, capture-recapture method,nomination methods, multiplier method, population surveys and generalized networkscale-up methods. The most important advantage of the multiplier method is that it ismuch more straightforward to use. However, studies of the multiplier method used toestimate the population prevalence of men who have sex with men in China publishedbetween July1,2003and July1,2013were reviewed. The median of studies usingthe multiplier method to estimate the population prevalence of men who have sexwith men in China was4-8times lower than the national level estimate.The network scale-up method was first proposed by Bernard, Killworth, Johnsen,and Robinson in1991and uses information collected in general population surveys toestimate the size of populations that have a high risk of HIV. The generalized network scale-up method proposed by Salganik et al. based on the network scale-upmethod lies in adjusting information transmission bias with the popularity ratio andinformation transmission rate. The multiplier method and generalized networkscale-up method were used to estimate the number of heavy-drug users in Curitiba,Brazil in2011. However, Salganik et al. found that the estimate yielded by thegeneralized network scale-up method was5times higher than that of the multipliermethod. It is possible that the generalized network scale-up method producedoverestimates or the multiplier method produced underestimates in the absence of agold standard for the number of heavy-drug users. Thus, Salganik et al. recommendedthat additional studies be undertaken to assess these two methods. This study aims toassess and compare the two methods for estimating the size of populations at highrisk for HIV, and to provide practical guidelines and suggestions for implementingthe two methods.MethodsStudies of the multiplier method used to estimate the population prevalence of menwho have sex with men and female sex workers in China published between July1,2003and July1,2013were reviewed. The MOOSE recommendations were used toconduct the reviews. Five electronic databases were searched in Chinese and English:PubMed, Wanfang Data, China National Knowledge Infrastructure, VIP Database forChinese Technical Periodicals, and Chinese BioMedical Literature Database.A survey of the general population using stratified two-stage cluster samplingwas conducted in the urban district of Taiyuan. For the first stage,174primary units(institutions/organizations/companies/governments) from all20industries wereselected from the sampling frame, with the probability of selection being proportionalto industry size. For the second stage,405second-stage units (departments) weredrawn from those chosen in the first stage wherein8,031third-stage units(respondents) aged18and above were interviewed and randomized responsetechnique was applied to eliminate response bias. A national-level estimate proposedby the National Center for AIDS and Sexually Transmitted Disease Control andPrevention in collaboration with UNAIDS/WHO in2007was selected as a reference to assess these two results.ResultsAfter the removal of5studies (3duplicate publications and2studies did not obtainappropriate data),13studies (1in English and12in Chinese) were from13cities.The estimated MSM population prevalence of the adult male population of the13cities were0.066%,0.249%,0.486%,1.220%, and6.884%for the minimum,25thpercentile, median,75th percentile, and maximum, respectively. The median (0.486%)of the13cities was4-8times lower than the national-level estimate (2.0-4.0%).After the removal of3duplicate studies,7studies remained (2in English and5in Chinese) that originated from7cities. The estimated FSW prevalence of the adultfemale population (aged15-49) of the7cities was0.777%,1.766%,2.485%,3.600%and4.365%for the minimum,25th percentile, median,75th percentile, and maximum,respectively. The median (2.485%) of the7cities fell within the range ofnational-level estimate (0.2-2.6%).The generalized network scale-up method allowed us to estimate the number ofMSM in Taiyuan as being26,870(95%CI:23,556,30,184), which corresponds to2.927%(95%CI:2.566%,3.288%) of the adult male population (aged15-49). Theestimates of generalized network scale-up method fall within the range ofnational-level estimate. The generalized network scale-up method allowed us toestimate the number of FSW in the urban district of Taiyuan as being11,787(95%CI:10,767,12,808), corresponding to1.284%(95%CI:1.172%,1.400%) of the femalepopulation aged15-49.ConclusionsWhen high-quality existing data are not readily available, the multiplier methodfrequently yields underestimated results. We thus suggest that the generalizednetwork scale-up method is preferred when sampling frames for the generalpopulation and accurate demographic information are available. |
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