| BackgroundThe first AIDS cases were reported in the United States in 1981. Since then, HIV infections appear to spread rapidly in the world. The estimated number of persons living with HIV worldwide is 33.2 million in 2007. In Shenzhen, the first HIV case was reported in 1992 while the cumulative infections reach 2614 at the end of 2007. However, surveillance data understate the magnitude of HIV epidemic because such data are subject to reporting delays, underreporting and changing patterns in HIV testing behaviours. The reasons are as follows: firstly, HIV is a chronic infection with a long incubation period, many newly infected persons may only be diagnosed in years after infection. Secondly, the susceptible population usually means IDUs, FSWs, ISWs, Clients, MSWs and MSMs in Shenzhen. They are easily discriminated, have frequent migration but few opportunities to accept HIV/STD education, and are likely to be untested or undiagnosed. Thirdly, lacking of professional staffs in this field is also concerned with the problem. From the above reasons or more, estimations and projections of HIV/AIDS epidemic status are recommended to describe the real situation for better policy, raising money and allocating it efficiently, evaluating the efforts of interventions. Multiple evaluated methods are developed, such as Component method, Back-calculation method, Epimodel, Workbook method, Estimation and projection package(EPP), Spectrum model, Asian epidemic model(AEM) and Goal model. Workbook method is popular in China, while more and more attention is paid to AEM.The Workbook method is built on the process of identifying groups at high risk of becoming infected with HIV, estimating the size and HIV prevalence of those groups, and combining the groups to obtain an estimated number of adult HIV infections in the places with concentrated or low level epidemics.AEM, which is a process model for exploring HIV policy and programme alternatives in Asia, considers HIV transmission within a population aged 15 and above. The population is then divided into 7 compartments (Clents, FSWs, MSMs, MSWs, IDUs, GMs and GFs) and lots of fomulars, designed in the AEM intenal model, are used to caculate the number of new infections, current infections and cumulative infections. AEM will produce a fit curve by adjusting the transmission probabilities and cofactors, and then generate useful outputs for policy and programming.Objectives1. To estimate the number of current HIV infections using Workbook method.2. To project the past, current and futrue state of HIV/AIDS epidemic in Shenzhen, and evaluate the effects of baseline scenario and 4 expanded intervention scenarios.3. To analyze the strengths and limitations of Workbook method and AEM, explore the applicability of AEM in China, and provide a certain useful information on HIV/AIDS epidemic projections.Material and methodsMaterial: Cumulative number of reported HIV/AIDS cases and their individual information, sentinel surveillance data, comprehensive behavioural surveillance data, epidemic investigation results and screening test results from 1992 to 2006, demographic information from 1980 to 2006 were collected. Method 1: According to Workbook method, Clients, FSWs, MSWs&MSMs and IDUs were identified to be the higher risk groups in Shenzhen. Data bank was built up to collect data and evaluate their quality. The best data were chosen to put in computer and results could be observed after consistency check.Method 2: The AEM had much more stringent input requirements than Workbook method. The inputs fell into a number of general categories: population size, heterosexual behaviours, injection behaviours, same sex behaviours, epidemic factors, prevalece of each subgorups and migration parameters. After data collection, the best data were chosen to put in EXCEL table, and then imported to AEM process. The process found the best fit status and then produced the results. This study had designed 4 expanded intervention scenarios to evaluate the effects of different intervention, such as encouraging condom use among MSWs&MSMs, reducing needle sharing among IDUs, reducing the prevalence of STDs and so on.Results1.Results from Workbook methodThe estimated number of current infections of HIV/AIDS was 4199, including 1695 IDUs, 699 MSWs&MSMs, 309 FSWs, 1116 Clients, 102 IDUs'partners, 9 MSWs'partners or MSMs'partners, 28 FSWs'partners and 138 Clients'partners.2.Results from AEMNumbers of new infections, current infections, cumulative infections in 2006 were 762, 4177 and 4683, and the epidemic would arise in future. The number of male new infections increased rapidly and accounted for more than 80% of the total number of new infection. The major mode of transmission was needle sharing before 2007, while after that time, unprotected sex behaviour, especially among MSWs&MSMs, became more and more important.The projection results of 4 expanded intervention scenarios showed that, scenario1, 2, 3 and 4 could avert 7217, 8727, 9623 and 9755 new infections separately, knowing that the scenario 1 had a major impact as it could prevent 6792 HIV infections among MSWs&MSMs.3.Comparision of projection results and surveillance data Compare the estimated results of current infections in 2006 from the 2 mathematical model with the number of cumulative infections from sentinal surveillance. The results showed that total number of current infections from Workbook method and AEM were 4199 and 4177, while there was some difference in projecting numbers among subgroups.Compare the scenario 4 projection results with surveillance data on new infections in 2007. These results showed that the AEM projections fit to the surveillance data very well.Conclusion1. The number of current infections at the end of 2006 in Shenzhen estimated by Workbook method and AEM is very close, which is about 2 times more than the HIV cumulative number from sentinal surveillance.2. AEM baseline projection results show that, if the intervention effect remains as it is in 2006, HIV/AIDS epidemic will arise in the coming 10 years, especially among MSWs and MSMs, while intervention measures in different scenario can largely avert new infections. Accordingly, comprehensive intervention is needed to yeild the most, but effective intervention among MSWs&MSMs is urgent.3. AEM projections reasonably reproduce epidemic trends in the coming years, but it is better to apply this mathematical model to data rich districts for its stringent input requirements. Either Workbook method or AEM has its strengths and limitations, therefore we need to combine the information from the 2 methods when projecting or analyzing the HIV/AIDS epidemic.In a word, this study makes an initial explore of AEM, and describes its validity by comparing its projection results with the data from surveillance and Workbook method. We hope it can provide a certain useful information of HIV/AIDS epidemic estimation about AEM. |
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