Estimated direct medical cost per syphilis case
There were 3767 patients with syphilis diagnosed at PUMCH from 2008 to 2018, whose demographic features were presented in Table1. Among 3767 patients, 1749 patients (46.81%) received treatment in our hospital, including only three cases of congenital syphilis (Table 1). The median and extreme value of costs for examination and treatment were characterized by age, gender, and syphilis stage (Table1). The highest median value of total cost was obtained in tertiary syphilis (US $ 186.14), followed by congenital syphilis (US $ 96.92), secondary syphilis (US $ 56.87), primary syphilis (US $ 48.99), and latent syphilis (US $ 46.74). To avoid underestimating of direct medical cost per syphilis case, only the data about direct medical costs in 1746 patients, including primary syphilis (n=151), secondary syphilis (n=518), tertiary syphilis (n=50) and latent syphilis (n=1027), was used to estimate direct medical cost per syphilis case according to different syphilis stage. The data about direct medical costs in three cases of congenital syphilis were excepted due to such a small sample size. Based on 36 months follow up, the estimated average costs per case was obtained as US $ 134.43 in primary syphilis, US $ 119.24 in secondary syphilis, US $ 503.76 in tertiary syphilis and US $ 97.59 in latent syphilis. (Table s1)
Distribution of syphilis cases in China
In 2016, there were 438199 cases newly reported in China. The highest yearly incidence of total syphilis was reported in Xinjiang (89.05 cases per 100 000), followed by southeast coast area (48.73-62.16 cases per 100 000), including Zhejiang, Shanghai, Fujian, Hainan and Guangdong, and western regions (48.47-56.70 cases per 100 000), including Ningxia, Qinghai and Chongqing (Figure s1). Lorenz curve in Figure s2a showed the distribution of syphilis cases in 31 Chinese provincial districts in relation to the population in each district in 2016. The X-axis represents the cumulative proportion of the population of each provincial district, and the Y-axis is the corresponding cumulative percentage of the number of syphilis cases. Each line segments between adjacent marked points along the Lorenz curve represents a single province, ordered by ascending syphilis incidence. About 21% of the syphilis occurred in the 10% of the population in southeast coast area and western regions. The value of the Gini index of the number of syphilis cases in 31 Chinese provincial districts in relation to the population in each district in 2016 was 0.27, indicating moderate equality in the distribution of syphilis cases.
Yearly incidence of syphilis in China rapidly increased from 7.12 to 30.44 per 100000 persons from 2004 to 2012, and slowly increased from 30.44 to 31.97 per 100000 persons from 2012 to 2016 (Figure s2b). The value of the Gini index of the number of syphilis cases in 31 Chinese provincial districts in relation to the population in each district continuously decreased from 0.52 to 0.27 from 2004 to 2013, and stabilized around 0.27 from 2013 to 2016 (Figure s2b). The value of the Gini index ranged from 0.52 to 0.42 from 2004 to 2009, indicating high inequality in the distribution of syphilis cases, 0.39 to 0.35 from 2010 to 2011, indicating inequality in the distribution of syphilis cases, and 0.29 to 0.27 from 2012 to 2016, indicating moderate equality in the distribution of syphilis cases.
Distribution of economic burden caused by direct medical cost of syphilis in China
The estimated absolute and relative directed medical costs of syphilis except for congenital syphilis were US $ 46.89 million and 3.99 per million of GDP, respectively, in China in 2016. The estimated absolute and relative directed medical costs in 31 Chinese provincial districts in 2016 were mapped in Figure 1A and 1B, respectively. Among 31 Chinese provincial districts, Guangdong had the largest absolute cost for syphilis (US $ 5.49 million), followed by eastern regions, including Zhejiang (US $ 3.73 million), Jiangsu (US $ 2.69 million), and Anhui (US $ 2.49 million). However, the largest relative cost as percentage of GDP was observed in Xinjiang (15.78 per million of GDP), followed by western regions (6.14-7.86 per million of GDP), including Ningxia, Yunnan, Qinghai, Xizang, Chongqing and Guizhou, and Hainan (7.80 per million of GDP) and Anhui (6.78 per million of GDP).
Bubble chart was drawn to present the relative medical cost of syphilis in 31 Chinese provincial districts from 2004 to 2016. (Figure 2) The largest relative cost as percentage of GDP was always observed in western region (i.e., Guangxi or Xinjiang) from 2004 to 2016. Between 2009 and 2016, a yearly relative medical cost more than 5.01 per million of GDP was observed in 7 to 9 provinces in western region, 3 to 5 provinces in eastern region, 1 to 4 provinces in central region, 1 to 2 provinces in northeastern region. By 2016, the relative cost had been tending to decline in all of the provinces in eastern and northeastern regions, except for Shandong, Hebei, Hainan and Liaoning. However, no downward trends of the relative cost had been observed in more than half of the provinces in western and northeastern regions. Lorenz curve in Figure 3a showed the distribution of the direct medical cost of syphilis in 31 Chinese provincial districts in relation to GDP in each district in 2016. The X-axis represents the cumulative proportion of the GDP of each provincial district, and the Y-axis is the corresponding cumulative percentage of the direct medical cost of syphilis. Each line segments between adjacent marked points along the Lorenz curve represents a single province, ordered by ascending relative costs, which were defined as the direct medical cost in per million of GDP. About 20% of the direct medical cost of syphilis occurred in certain regions with only 10% of the GDP. The value of the Gini index of the direct medical cost of syphilis in 31 Chinese provincial districts in relation to GDP in each district in 2016 was 0.27, indicating moderate equality in the match between direct medical cost of syphilis and GDP.
Absolute medical cost of syphilis in China increased from US $ 11.15 million to US $46.89 million from 2004 to 2016. Relative cost in China increased from 2.85 to 5.26 per million of GDP from 2004 to 2010, and decreased from 5.26 to 3.99 per million of GDP from 2010 to 2016. (Table s2 and Figure 3b) The value of the Gini index for the direct medical cost of syphilis in 31 Chinese provincial districts in relation to GDP in each district decreased from 0.40 to 0.25 from 2004 to 2014, and slowly increased from 0.25 to 0.27 from 2014 to 2016. (Table s2 and Figure 3b) The value the Gini index was 0.40 in 2004, indicating high inequality in the match between direct medical cost of syphilis and GDP, and ranged from 0.33 to 0.40 (0.399 in 3 decimal places) between 2005 and 2011, indicating inequality in the match between direct medical cost of syphilis and GDP, and 0.25 to 0.27 between 2012 and 2016, indicating moderate equality in the match between direct medical cost of syphilis and GDP.