In this study, we conducted a cross-sectional HIV-1 molecular epidemiological study to track the characteristics and distribution of HIV-1 genotypes and TDR in newly diagnosed infections in Sichuan. For the first time, the TDR of HIV-1 infection in Sichuan, which was one of the highest AIDS epidemic provinces was analyzed.
This results were inconsistent with the national monitoring in 2016 and the survey results in some other areas[20, 21], while were similar to that of the study conducted in Sichuan 2014. Compared with the 2014 survey, it is found that the PLWH in this study were older and less educated, shown that elderly people with low educational background in our province are the people who need to be paid attention to. Heterosexual transmission is the main route of infection, in which the proportion of commercial heterosexual is the highest, moreover, results of transmission cluster analysis showed similar results. It showed that this group of the PLWH has spread in a short time, indicating that commercial sexual activity is an important factor causing HIV transmission. 67.65% of HIV-infected men were over 50 year-old ,who infection came mainly from commercial sexual activity, as such groups often exist with spouse separation and widowhood, their sexual needs are hard to be met, and their cognition of AIDS is insufficient. Note that although men younger than 25 years old account for a low proportion of infected people, most of their infection routes are male transmission, which increases with the decrease in age.There was little difference in transmission routes among women of different ages, mainly noncommercial heterosexual transmission, suggesting that further attention should be paid to the source of infection of such populations for more accurate intervention.
A total of 15 HIV-1 genotypes were detected, and 4 URFs were identified. It showed a much more gene diversity of HIV in Sichuan, which may reflect the active mobility of people across the province. Similar to the survey in 2014, the main prevailing HIV-1 genotypes in Sichuan remain CRF07_BC and CRF01_AE, but the proportion decreased slightly, which was obviously different from other regions that CRF01_AE (i.e., Anhui, liaoning and Guangxi), B (i.e., Henan), CRF08_BC (i.e., Yunnan) was the dominant strain[21, 23–25]. CRF01_AE was identified in the 1990s as being imported from Thailand to Southwestern China (i.e., Yunnan and Guangxi) in commercial sex worker (CSW)[26, 27]. The recombinant subtypes of CRF07_BC and CRF08_BC have common origin which were first circulating in intravenous drug users (IDUs) in Yunnan[8, 28], which was introduced fromand from Liangshan to Sichuan. The proportion of CRF08_BC and CRF85_BC among HIV-1 PLWH in Sichuan increased from 4.96% and 3.39–8.87% and 5.17% in 2019, and eight different subtypes were identified more than in 2014. The proportion of URFs also increased significantly, which may be due to the complexity of HIV-1 gene pool caused by long-term epidemic.The genetic diversity of HIV-1 is abundant in Sichuan, in addition to the known circulating recombinant forms (CRFs), some URFs were also detected in Sichuan. URFs contributed to the formation of novel CRFs, recently, new CRFs were identified in Sichuan[12, 13, 31].
In our study, most of the infected people entering the transmission network are heterosexual transmission, but, research in Guangxi showed that most HIV-1 infection clusters were MSM, and Liu suggested that factors such as sex, mode of transmission, education level and ethnicity were not significantly correlated with access to the genetic transmission network in Liangshan. It showed that the situation of transmission networks in different regions was various, and targeted prevention and control measures need to be put forward for different regions, especially in cities with high clustering rate.In addition, it was observed a high clustering rate of subtype B (66.67%, 24/36), which was much higher than other subtypes (10%-25%). This result found out a molecular cluster that rapidly propagates in a short time, it showed that timely molecular subtype monitoring is conducive to more accurate prevention and control of HIV transmission.
The results also showed that there were significant differences in the distribution of subtypes in different regions. The frequent reconstitution of the HIV genome will accelerate the evolution of the HIV, which may lead to the emergence of a highly adaptive virus [34, 35]. It was worth noting that the subtypes in Leshan, Chengdu and Luzhou are more complex. The existence of multiple subtypes increasees the probability of mutual recombination to form new subtypes, therefore, it is necessary to further strengthen the monitoring of HIV subtypes in Sichuan Province, timely grasp the epidemic trends and reduce the generation of recombinant subtypes.
Recently, the trend of virus strain diversification in Sichuan province was gradually obvious, CRF55_ 01B, CRF79_0107, CRF59_01B[38, 39] were found for the first time in China's MSM population. In this study, these three subtypes were detected in men, only one female was transmitted by spouse, but only 38.46% (5/13) CRF55_ 01B, 40% (2/5) CRF79_0107 PLWH were transmitted by MSM, and the rest were heterosexual sexual transmission. There may be a concealed sexual orientation because of the social homosexual cultural identity and discrimination. Some MSM will have sex with women inside and outside the marriage, and increase the difficulty of AIDS prevention and treatment, and suggest that the proportion of homosexual transmission in this province may be underestimated. CRF105_0108 was the subtype found for the first time among heterosexual people in Liangshan Prefecture, Sichuan Province, which was found that there was an aggregated epidemic in Luzhou, and one case is also found in Meishan, suggesting that this subtype may have spread in Sichuan Province, and 54.54% (6/11) PLWH infection with this subtype were transmitted by commercial heterosexual, indicating that commercial sex workers (CSWs) need to be further found in Luzhou to reduce virus transmission.
Another serious consequence of the high variability of HIV-1 is drug resistance, which is a new threat to epidemic control and can lead to treatment failure and further transmission of resistant HIV. Our study in Sichuan showed the overall prevalence of TDR was 5.55% among the 1297 participants, belonging to the moderate drug resistance level (5% - 15%). The result was higher than the currently reported national total prevalence rate and transmissible drug resistance rate of 3% - 5%[16, 42–44]. Su found through meta-analysis that the rate of transmissible drug resistance in Beijing, Henan and Hubei has reached the level of moderate drug resistance. The studies of Zhejiang and Shanghai [47, 48] showed that the rate of transmissible drug resistance has been greater than 10%, which may be due to the early start of antiretroviral treatment in some areas and large treatment coverage. The pretreatment drug resistance rate was 9.9% in Liangshan Prefecture from 2017 to 2018, the results were in keeping with our findings that the drug resistance rate of Liangshan was 9.8%. The high rate of TDR in some cities indicated that the monitoring of TDR rate should be carried out in these cities. It could be seen that the longer the antiviral time, the higher the proportion of drug resistance. With the increase in the number of people receiving antiviral treatment, the risk of HIV drug resistance also increases, which may lead to the increase the transmissible drug resistance rate, it directly affects the effect of antiviral therapy.The drug resistance survey results of infected people receiving antiviral treatment showed that the national acquired drug resistance rate was 8.6%, and the drug resistance rate of infected people who fail to inhibit the virus exceeds 50% [51, 52].
According to our study, TDR mutation frequency to NNRTIs was much higher than NRTIs and PIs, due to NNRTI had a low resistance barrier, and it was more prone to drug resistance. Because of the limited availability of drugs in China, the regimen composed of TDF, 3TC and EFV was currently the most commonly used free first-line therapy. The above three kinds of drugs exhibited the degree of resistance was mainly at a potential low level, therefore, the first-line treatment drugs can still be used continuously in Sichuan Province. The most frequent NNRTI-associated DRMs were V106 and E138, which were mainly resulted in low-resistance to RPV and DOR, whereas were K103N in whole country[16, 21]and V179D/E in Shanghai. There were 21 cases of DOR resistance, accounting for a high proportion, DOR is a new NNRTI, which has not provided through the NFATPI in China, suggesting that the use of DOR in the future needs to pay close attention to whether it will have a certain impact on the treatment effect. The proportion of K103N mutationin our study was also high, and it is highly resulted in resistant to EFV and NVP, these two drugs were free NNRTI drugs used in China, therefore, we need to be vigilant about the mutation of K103N. The NRTI-associated DRMs were K65KR/R, K70KR and M41L, among which K65KR/R mutation causes high resistance to d4T, DDI and TDF, but M184V, the most common mutation site of NRTI resistance, is not found in our study, which may be related to the current first-line treatment scheme and the low rate of NRTI resistance in Sichuan Province. The main DRMs of PI were M46 and Q58, which produced low or intermediate-resistance to NFV, and low-resistance to TPV/r. The most frequent DRMs M46 was consistent in previous reports[16, 43, 47], and the main DRMs Q58 could be related to the high prevalence of CRF07_BC in Sichuan. Thus, it was considered that, the mutation of drug resistance discovered in the study could be induced by the mutation of exogenous population or non-drug selection pressure.
However, our study has limitations. First, a potential sampling bias, on the one hand, in our study only one cross-sectional study was conducted, and the results could not be used to observe the dynamics of the local HIV epidemic, on the other hand, we could analyze only the samples that had been diagnosed, but those that had been infected but not diagnosed could not be included in the analysis. Second, our analysis of TDR concentrated only on NRTI, NNRTI and PI, not containing integrase inhibitors, which are increasingly infected people began using this drug.