Our study showed that the morbidity of AIDS in Chinese population increased from 1999 to 2018, which were consistent with the results of Yong-Chao and Zun-you Wu's study[10, 11]. The rising tendency was the most pronounced during 2002-2005. The possible reasons are the abuse of intravenous drug, the increase in the number of homosexual men and infection occurred after irregular blood collection[12]. Since the implementation of the blood donation law in 1998, the transmission of HIV through blood collection and supply has been controlled in China. At present, the transmission of HIV is mainly through sexual transmission[13-15]. The introduction of "four exemptions and one care" policy in 2006 and the implementation of the "six expansion and five strengthening" prevention and control measures in 2011 have also effectively slowed down the rising tendency of AIDS morbidity, which is consistent with our study results[16-18]. In addition, a research report on the global AIDS epidemic showed that compared with other countries, the current AIDS epidemic in China is at a low epidemic level[19].
Previous study indicated that the epidemic of gonorrhea in China rose rapidly in the 1970s, reached its peak in 1999, and then declined, which was consistent with our study results[20]. But our study showed that the morbidity of gonorrhea began to rising in 2012-2018, which was similar to that of the United States and the United Kingdom in the same years[21]. This phenomenon may be due to the expanded coverage of gonorrhea screening, the increased sensitivity of diagnostic methods and the increase in the number of MSM patients[22, 23]. Although our study indicated that the morbidity of gonorrhea in China from 1999 to 2018 had an overall trend of decline, it is still in the forefront of the notifiable infectious diseases, especially in 2018 its morbidity reached 9.58%, ranking fourth. Additionally, many studies found neisseria gonorrhoeae was resistant to many antibiotics, making the treatment of gonorrhea become a major challenge for clinicians in recent years[14, 24-26].
The results of our study showed that the morbidity of syphilis in China was on the rise during 1999 to 2018, which was contrary to the overall trend of gonorrhea incidence[20]. The trend changes in the both SIDs were similar to developed countries. On the one hand, this phenomenon may be due to the increased number of syphilis infection population in MSM; On the other hand, it mainly because the government launched a national plan on expanding syphilis screening in 2010, which led to an increase in the number of cases diagnosed as latent syphilis[27, 28]. And the related literature also suggested that syphilis morbidity rate was higher than AIDS in Chinese MSM population[10]. Our study indicated that the morbidity of syphilis had been increasing per year since it reached lowest level in 2003, and its morbidity was higher than that of AIDS and gonorrhea. Moreover, previous studies also showed that the majority of Chinese people's knowledge of syphilis is far lower than the standard of 10-year plan set by our country[27, 29, 30].
We also used hierarchical clustering analysis to describe the region distribution of three STIs. Compared with previous years, the current high incidence of the three STIs is mainly concentrated in the southeast coastal areas and Xinjiang. The reason for the high morbidity of STIs in southern cities is mainly due to the sexual disorder caused by the rapid increase of floating population in recent years. However, the cause of the high morbidity of STIs in Xinjiang still needs further study. The above results suggest that the government should strengthen the prevention and treatment of southeast coastal areas and Xinjiang.
Some limitations also need to be noted. First, the sample size of our study is very small. Second, the study data comes from passive monitoring, exact morbidity rates are hard to obtain, and reported morbidity rates may underestimate the true status of STIs. In final, the morbidity of infectious diseases is related to the natural environment, social economy and personal hygiene habits, which may lead to unstable prediction results.