AEM Model as a Suitable Tool for Estimating and Predicting the HIV/AIDS Epidemic in Sichuan Province
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IDUs, FSWs, and MSMs are the main factors fueling the HIV/AIDS epidemics in various Asian countries and regions. As the disease progresses, FSWs contribute to the infection of clients, while IDUs transmit the infection to their heterosexual partners. This heterosexual transmission is a noteworthy component of the epidemic in this region[7]. According to the characteristics of the epidemic in Asia, Dr. Tim Brown and other foreign scholars developed the Asian AEM, which is suitable for the estimation and prediction of the HIV/AIDS epidemic in the clustered epidemic region of Asia[8].
At the end of 2015, data from the Sichuan report indicated the main transmission route of PLWHA was heterosexual, accounting for 57.06% of cases, followed by injection of drugs (25.31%) and homosexuality (12.31%). Since 2010, the newly reported rate of HIV/AIDS sexual transmission in Sichuan Province has surpassed that of drug injections as the primary transmission route. Therefore, the HIV epidemic in Sichuan Province is characterized by a clustered pattern with sexual transmission emerging as the main feature, which is suitable for the use of the AEM.
Gradual Increase in the Number of New HIV Infections and Persistent Rise in the Number of PLWHA
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According to the AEM fitting results, the number of new HIV infections in Sichuan increased rapidly from 1994, peaked in 2004, experienced a slight decline, showed a gradual increase after 2007, and then declined again in 2015. By 2025, the number of PLWHA in Sichuan is projected to reach 212,168, while the HIV infection rate of the entire population in Sichuan is projected to increase to 0.306%. Analysis of the results revealed that the peak of new infections in 2004 was consistent with the peak of new infections among IDUs, while the peak of new infections in 2015 was consistent with the increase in new infections among MSMs, FSWs, and clients. The decline in the number of new infections after 2004 was largely due to the initiation of antiretroviral treatment. In Sichuan, free antiviral treatment was introduced in 2003, which has directly led to a decline in the number of new HIV infections in 2003. In 2004, the indication for free antiviral treatment was a CD4+T lymphocyte count of < 200; in 2012, the indication for treatment was changed to a CD4+T lymphocyte count of < 350; in 2015, the indication for treatment was further adjusted to a CD4+T lymphocyte count of < 500; and in 2016, the requirement for treatment based on CD4+T lymphocyte count was abolished. Treatment is now available for all individuals with HIV infection. Each change in the standard of care has led to a decline in the number of new infections. With the expansion of the coverage of antiviral treatment and the improvement in antiviral treatment effects in Sichuan, the viral load was effectively suppressed, the fatality rate of patients decreased, and the survival cycle was prolonged. Therefore, the number of new infections tended to stabilize; however, the number of PLWHA rapidly increased.
High Prevalence of Infection among Men with an Increasing Proportion of Women Affected
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In 2015, the PLWHA population comprised 97,724 men (75.89%) and 31,042 women (24.11%). By the end of 2025, 159,970 men (73.51%) and 53,198 women (26.49%) are predicted to comprise the PLWHA population. The HIV infection rate in the entire population of Sichuan was higher in men than in women. Based on the projected infection rates for each population, the five groups with the highest HIV infection rates were male IDUs, MSMs, MSWs, female IDUs, and clients of FSWs, with four out of these five groups being men. As can be observed from the number of PLWHA, MSMs, IDUs, and clients of FSWs account for more than 70% of all infection cases. Therefore, we believe that HIV/AIDS infections primarily occur among men.
Based on the prediction results, the proportion of women infected is increasing, from 24.11% to 26.49%. Approximately 90% of new infections in women were observed among low-risk women, and more than 90% of new infections in low-risk groups occurred among women. According to the predicted results of transmission routes, the infection in newly infected low-risk women was primarily transmitted from one spouse to another. Based on these results, we believe that HIV infection in Sichuan is spreading from a high-risk male population to a low-risk female population.
Heterosexual Transmission as the Main Route of HIV Transmission
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The prediction results of the AEM show that among the PLWHA in Sichuan, the proportion of IDUs is decreasing, the proportion of MSMs is increasing, the proportion of FSWs and clients of FSWs is increasing, and the proportion of low-risk male and female heterosexual transmission is increasing. Therefore, heterosexual transmission has replaced the IDU as the primary route of infection.
Prediction of HIV Epidemic Trends under Different Levels of Comprehensive Interventions
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If the comprehensive intervention coverage rates of FSW/IDU/MSM increase from the current situation to 50%, 60%, 70%, 80%, and 90%, respectively, in 2025, a total of 7,822, 9,539, 11,002, 12,645, and 13,910 new HIV infection and AIDS cases will be avoided, respectively. This could reduce the number of PLWHA to 38,476, 47,245, 55,621, 65,428, and 75,679, respectively, by 2025. If the intervention coverage rate is expanded to 90%, the HIV infection rates would be reduced from 0.306% to 0.197%.
If the coverage rates of clean needle exchange and methadone maintenance treatment increase to 14%, 18%, 22%, 26%, and 30% among IDUs, respectively, in 2025, a total of 1,486, 2,125, 2,606, 3,415, and 3,954 new HIV infections in the whole population could be avoided, respectively. Additionally, the number of PLWHA in Sichuan can be reduced by 5,576, 7,266, 8,381, 10,581, and 12,091, respectively, in 2025.
If the intervention coverage rates of MSM and MSW increase to 50%, 60%, 70%, 80%, and 90%, respectively, by 2025, and the condom utilization rates will increase to 75%, 80%, 85%, 90%, and 95%, respectively; hence, 4,260, 4,956, 5,604, 6,269, and 6,912 new HIV/AIDS infections in the whole population will be avoided, and 2,1841, 2,6482, 31,323, 36,602, and 42,860 PLWHA in Sichuan will be reduced.
In 2025, if the intervention coverage rates of FSW increase to 50%, 60%, 70%, 80%, and 90%, the condom use rates of FSWs and clients of FSWs will increase to 75%, 80%, 85%, 90%, and 95%, respectively. This will prevent 2,614, 3,034, 3,402, 3,797, and 4,175 new HIV infections in the whole population, and reduce 11,882, 14,502, 17,102, 19,811, and 22,821 PLWHA in the province, respectively.
In summary, improving the coverage rate of clean needle exchange and methadone maintenance treatment in IDUs and improving the condom utilization rate in MSMs, FSWs, and clients of FSWs are the most influential factors in predicting the continuous rising trend in the number of HIV/AIDS patients living in Sichuan Province from 2015 to 2025. Based on the above results, a comprehensive intervention targeting high-risk groups would yield the most significant impact if sufficient funds are available. In cases of limited funding, the primary focus should be on addressing male population behavior and implementing interventions for MSMs and MSWs. Strengthening interventions in these groups can effectively reduce the number of new HIV infections and cases of PLWHA. Following this, increased intervention among the FSWs is recommended; meanwhile, intensive intervention among the IDUs can reduce the number of HIV infections and cases. This analysis is rooted in the observation that HIV is primarily spread in Sichuan through sexual contact, making targeted interventions in this domain the most beneficial. Emphasizing the correct usage of condoms remains the most effective method of preventing the sexual transmission of AIDS.
PLWHA Epidemic “Inflection Point” in Response to Different Interventions
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According to the prediction results of the AEM, if the current intervention coverage rate remains unchanged, the number of PLWHA in Sichuan will continue to increase, reaching 212,168 (0.306%) by 2025. To alter the trajectory of increasing HIV prevalence in Sichuan Province and transition to a turning point of decline over the next decade, a comprehensive intervention coverage rate of more than 60% is essential for IDUs, MSMs, MSWs, and FSWs. If only the proportion of a single group increases, the intervention efforts will not be able to reverse the rising trend in Sichuan. To limit the number of PLWHA to 180,000 in Sichuan, it is imperative to either increase the comprehensive intervention coverage rate of the whole population to more than 50% or increase the condom use rate of the MSM/MSW population to more than 90%.
Expanding the Coverage of Needle Exchange and Methadone Maintenance Interventions
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The results of this study underscore the potential impact of increasing the coverage of clean needle exchanges and methadone maintenance treatment among IDUs in reducing the number of new HIV infections and PLWHA in IDUs and the entire population. If the intervention coverage rate of needle exchange/methadone maintenance therapy among IDUs is increased to more than 14% (i.e., ensuring that the proportion of people who do not receive needle exchange or methadone treatment intervention is < 58%), 1,486 new HIV infections can be avoided, the number of PLWHA can be reduced to 5,576, and the number of new HIV infections in Sichuan will decrease annually.
Sichuan Province is close to the “Golden Triangle”. Drug traffickers have been using it as an important drug trafficking channel, a transit center, and an underground sales market from the “Golden Triangle” to the mainland due to its special geographical location. The results of this study also predicted that the largest proportion of new infections will continue to occur among drug users. Therefore, we suggest that Sichuan Province focus on IDUs, strengthen methadone maintenance treatment, improve the treatment coverage and maintenance rate of the IDU population, and improve community drug rehabilitation and referral mechanisms. Moreover, clean needles should be provided to drug users in areas where methadone replacement therapy is not available to reduce the risk of infection through needle sharing among drug users[9].
Increasing the Rate of Condom Use among MSMs and FSWs
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The prediction results show that the proportion of HIV infections among IDUs will decrease annually, whereas the proportion of HIV infections among MSM will increase annually. The majority of MSMs in Sichuan are young people, including male college and technical secondary school students[10]. They generally have a high willingness to accept AIDS prevention and intervention services and sufficient AIDS-related knowledge. In this population, after receiving a large number of AIDS awareness interventions, the condom utilization rate did not significantly improve[11], unsafe sex continued to exist among MSMs, and existing interventions failed to achieve the expected effect. Therefore, MSMs and MSWs will be key intervention groups in the future. Increasing the condom use rate in these groups will effectively control the number of newly infected HIV patients and PLWHA in Sichuan.
FSWs are a bridge group in the commercial sex service network, and the risk of HIV transmission is relatively high among IDUs, MSMs, clients of FSWs, and low-risk populations. Although the monitoring data show that the HIV-positive rate of FSW has remained low, ranging from 0.3% to 0.5%, the data may be more indicative of new infection rates rather than prevalence rates due to the influence of sampling points and the high mobility of the population sampled. After testing for HIV antibody positivity, FSWs choose to change prostitution venues or relocate to avoid potential isolation or the exposure of their privacy related to sexual services. The substantial mobility of this group presents challenges in monitoring. Thus, the annual rate of HIV infection detected at sentinel sites is likely reflective of the rate of new HIV infections among FSWs rather than its prevalence. BED capture-ELISA tests conducted by the Sichuan Center for Disease Control and Prevention[12] revealed fluctuating new infection rates of HIV-1 among FSWs between 0.09% and 0.51% from 2011 to 2015, a statistically significant difference. Similar results were confirmed by the new infection rate and sentinel monitoring of the incidence rate. Therefore, FSW should remain the focus of future interventions.
Strengthening Interventions for Low-Risk Population
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The results of the AEM in this study showed that the proportion of PLWHA (men and women) in Sichuan is increasing. At present, AIDS intervention work in Sichuan is mainly concentrated in the high-risk population; therefore, we believe that intervention work in the low-risk population needs to be strengthened. The primary infection routes in the low-risk population in Sichuan were through spousal and casual sexual transmission, often involving multiple sex partners.
The results of cohort studies in China showed that the transmission rate of HIV between couples of single-positive families was 30.0%, and the male-to-female transmission rate was higher than the female-to-male transmission rate[13]. Similar studies conducted both domestically and internationally have confirmed that the probability of sexually transmitted HIV from men to women is higher than that from women to men in couples of single-positive families[14,15]. This observation may be attributed to the higher HIV concentration in semen than in vaginal secretions or the differences in male and female genital anatomy, leading to more extensive and prolonged contact for women with the virus. AIDS prevention and control efforts should focus on male propaganda and interventions. The survey results of Sichuan Province indicate that the condom utilization rate of couples in single-positive families remains low. Only 32.35% of HIV-positive individuals consistently use condoms when engaging in sexual activities with a fixed partner or spouse, even after being informed of the infection[16]. Early notification of the spouse's infection is recommended. Some researchers have shown that spouses receiving notification services and HIV testing within 3 months can help reduce the risk of spousal transmission in couples with single-positive families[17]. In addition, regular follow-ups, guidance for infected people to use condoms correctly during sexual intercourse, and timely antiviral treatment of AIDS should be effective in reducing HIV transmission between spouses and sexual partners.
Liangshan Prefecture in Sichuan Province bears the most severe HIV/AIDS epidemic in the province and is home to the Yi ethnic minority group. In addition to Liangshan Prefecture, ethnic minorities such as Tibetans and Qiang in Ganzi and Aba Prefectures are prevalent in agricultural and pastoral areas, where non-commercial polysexual partners are more common. Owing to the relatively backward economy, limited healthcare infrastructure, low levels of public education, and language barriers in ethnic minority areas, it is difficult to implement effective public awareness campaigns and AIDS prevention efforts. Traditional health education has little effect on AIDS, and the public awareness rate of AIDS is relatively low. Some ethnic minority communities have relatively open attitudes toward sex. In some situations, such as ethnic traditional festivals, fairs, weddings, and funerals, people tend to have non-commercial and non-fixed sexual behaviors. The lack of condom availability and low utilization rates increase the risk of sexually transmitted diseases and AIDS transmission within these populations[18]. To address these challenges, it is recommended to engage local village doctors and community members as health education advocates in ethnic minority rural areas, conduct AIDS knowledge dissemination and promote the use of condoms among villagers, improve villagers’ awareness of AIDS and their self-protection ability, and strengthen awareness of condom use. In addition, the availability and accessibility of condoms should be ensured, and free condom self-collection points should be established in places where villagers gather, such as village activity rooms and clinics. Thus, condom access can be enhanced, condom use can be increased, and sexual transmission of AIDS can be reduced.
In addition, the active development of personalized intervention software is an important intervention measure for preventing HIV infection in the future, especially in low-risk groups. Combining the insights gained from the AEM with the development of personalized software based on different risk areas holds the potential for achieving enhanced and more comprehensive protection for low-risk groups.
Expanding the Coverage of Antiviral Treatment and Increasing the Number of People Receiving Antiviral Treatment
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The results of this study showed that the case fatality rate of AIDS will decrease annually from 2015 to 2025, which also reflects the effectiveness of current HIV antiviral treatment. Currently, highly active antiretroviral therapy (HAART) is the most effective AIDS treatment worldwide. Cohort studies[19] have shown that HAART effectively reduces mortality and prolongs survival. Clinical studies[20] have shown that HAART can effectively increase the number of CD4+T lymphocytes and reduce the viral load. Sichuan Province began implementing free antiviral treatments in 2003. The indications for receiving free treatment include a CD4+T lymphocyte count of < 200 in 2004, a CD4+T lymphocyte count of < 350 in 2012, and a CD4+T lymphocyte count of < 5 00 in 2015. The CD4+T lymphocyte criterion was eventually abolished in 2016, and the number of people receiving ART treatment increased. The results of the AEM also suggest that an increase in the number of people treated with ART and the treatment coverage rate can promote a decrease in the number of new HIV infections; the greater the number of people treated, the greater the decline. ART effectively suppresses the viral load and reduces infectivity, thereby reducing the number of new infections. With the change in CD4+T lymphocyte treatment standards, the number of people requiring treatment increases. In addition to newly infected people with HIV, PLWHA who do not meet the criteria for CD4+T lymphocyte treatment will become the target of antiviral treatment, underscoring the considerable treatment gap that persists. Therefore, it is necessary to strengthen the monitoring and testing in Sichuan Province to increase the proportion of HIV-infected persons and patients, strengthen departmental coordination, expand ART coverage of antiretroviral treatment, and increase the number of people receiving antiretroviral treatment.