The overall epidemic situation of RIDs from 2010 to 2019
From 2010 to 2019, there were 18 746 367 notifiable cases of RIDs in mainland China. The incidence rate of RIDs increased from 109.85/100 000 in 2010 to 340.94/100 000 in 2019. PTB was the most prevalent and accounted for 42.08% ~ 67.62% of RIDs notifiable cases between 2010 and 2018, while seasonal influenza was most prevalent in 2019, accounting for 74.31% of notifiable RIDs cases in 2019. During the period 2010 to 2019, PTB had the highest average annual incidence rate (63.15/100 000), followed by seasonal influenza (46.79/100 000), mumps (20.27/100 000), scarlet fever (3.98/100 000), rubella (1.54/100 000), measles (1.43/100 000), pertussis (0.60/100 000) and epidemic cerebrospinal meningitis (0.01/100 000). The incidence of HPAI and H7N9 were extremely low, there were only 14 notifiable cases of HPAI during 2010-2015 and 1385 notifiable cases of H7N9 seasonal influenza which mainly occurred from 2013 to 2017. No diphtheria cases were reported (Table 1).
During the 10 years, a total of 28 816 death cases were reported for the 12 RIDs, and the mortality decreased from 0.24/100 000 in 2010 to 0.23/100 000 in 2019. PTB accounted for 89.70%~98.37% of the RID death cases from 2010 to 2019, ranking the first, followed by seasonal influenza (0.26%~8.23%). There were a total of 928 reported deaths from other RIDs during the 10 years, including H7N9 influenza (561 deaths), epidemic cerebrospinal meningitis (173 deaths), measles (153 deaths), pertussis (15 deaths), HPAI (10 deaths), mumps (7 deaths), scarlet fever (6 deaths), and rubella (3 deaths).
Age-specific incidence rates and mortalities of the six chosen RIDs from 2010 to 2018
The age-specific incidence rates of the six RIDs were shown in Fig. 1. For PTB, the highest age-specific incidence rate was in the group of people aged 65 years old and over, and varied from 183.78/100 000 in 2010 to 131.81/100 000 in 2018 (Fig. 1A), however, our collected data showed that the notifiable cases of PTB were the most in the group aged 40-64 and accounted for 39.68% to 42.39% during 2010 to 2018. Pertussis was mostly observed to occur in children, and the 0-4 age group carried the highest incidence rate (1.75/100 000 in 2010 to 23.92/100 000 in 2018) and majority of incidence cases (accounted for 84.47% to 91.90% during 2010 to 2018) (Fig. 1B). For the measles, the 0-4 age group owned the highest incidence cases and rate, followed by the 15-39 age group (Fig. 1C). The most incidence cases and the highest rate of seasonal influenza were both in the 0-4 age group, followed by the 5-14 age group (Fig. 1D). In contrast to the seasonal influenza, the most incidence cases and the highest rate of mumps were both in the 5-14 age group, followed by the 0-4 age group (Fig. 1E). The incidence cases of rubella were mostly found in the 15-39 age group, however, the highest incidence rate was found in people less than 15 years old (Fig. 1F).
Due to the relative higher burden posed by the PTB and seasonal influenza of the six chosen RIDs, we only analyzed the age-specific mortalities of these two RIDs (Fig. 2). We found that the reported deaths and mortality of the PTB all increased with age, and the highest were both in people aged 65 and over (Fig. 2A). For the seasonal influenza, the highest reported deaths were in the 40-64 age group, while the mortality was more frequent in the 0-4 age group and 65+ years groups (Fig. 2B).
Temporal trends of incidence rates and mortalities of the six chosen RIDs from 2010 to 2018
The temporal trends of the age standardized incidence rates of the six chosen RIDs were shown in Fig. 3. We observed that the six RIDs were with different temporal trends from 2010 to 2018. The age standardized incidence rate of PTB declined yearly from 76.81/100 000 in 2010 to 57.16/100 000 in 2018, with -3.57% APC (95% CI: -4.03 ~ -3.12, p<0.001) (Fig. 3A), while the age standardized incidence rate of pertussis increased from 0.11/100 000 in 2010 to 1.47/100 000 in 2018, with APC was 41.55% (95% CI: 27.63 ~ 56.99, p<0.001) (Fig. 3B), for the measles and mumps, both age standardized incidence rates remained stable over the nine years with APCs of -2.49% (95% CI: -25.12 ~ 26.99, p=0.828) (Fig. 3C) and -8.44% (95% CI: -17.16 ~ 1.20, p=0.076) (Fig. 3E), respectively, and the age standardized incidence rate of rubella declined with APC of -31.62% (95% CI: -42.96 ~ -18.03, p=0.002) (Fig. 3F). For the seasonal influenza, one joinpoint was identified in 2016, the age standardized incidence rate increased with APC of 25.93% (95% CI: 11.95 ~ 41.64, p=0.006) from 2010 to 2016, and increased with APC of 58.35% (95%CI: 15.49 ~ 117.13, p=0.016) from 2016 to 2018 (Fig. 3D).
We also analyzed the temporal trends of the age standardized mortalities of PTB and seasonal influenza (Fig. 4). For the PTB, the age standardized mortality declined from 0.25/100 000 in 2010 to 0.20/100 000 in 2018, and one joinpoint was found in 2015, from 2010 to 2015 the APC declined by -8.71% (95% CI: -11.09 ~ 6.26, p=0.001) and increased by 9.20% (95% CI: 3.15 ~ 15.60, p=0.013) from 2015 to 2018 (Fig. 4A). For the seasonal influenza, the age standardized mortality remained stable across the decades, although one joinpoint was identified in 2015, with the APCs of -31.51% (95% CI: -54.91 ~ 4.03, p=0.066) from 2010 to 2015 and 81.88% (95% CI: -23.77 ~ 333.97, p=0.129) from 2015 to 2018 (Fig. 4B).
Seasonal distributions of incidence rates of the six chosen RIDs from 2010 to 2018
The results from seasonal decomposition analysis showed that almost all of the six RIDs occured in winter or spring, and each has its own characteristics (Fig. 5). The incidence rate of PTB presented two peaks in Nov and Mar, respectively (Fig. 5A). The high-incidence seasons of seasonal influenza were in Dec, Jan, Feb and Mar with a peak in Jan (Fig. 5D). We then found an interesting phenomenon that the peak-incidence seasons of the other four RIDs appeared in sequence after the influenza seasons. For example, measles showed the peak incidence in Apr (higher incidence in Mar, Apr and May, Fig. 5C), rubella in May (higher incidence in Apr, May and Jun, Fig. 5F), mumps in Jun (higher incidence in May, Jun and Jul, Fig. 5E), and pertussis in Jul (higher incidence in Jun, Jul and Aug, Fig. 5B).
Spatial distribution of incidence rates and mortalities of the six chosen RIDs from 2010 to 2018
In most provinces of mainland China, the majority of RIDs incidence trends were consistent with the national trend, with only a few provinces showing opposite trends in the incidence of a few RIDs. (Table 2). The incidences of the six chosen RIDs showed different spatial distributions in the 31 provinces (Fig. 6). By comparing to 2010, the incidence rates of PTB in 2018 were found decreased in 27 provinces, with the greatest decrease in Gansu (57.30%) of northwestern China, while found increased in four provinces, including Tibet, Qinghai, Yunnan and Xinjiang with percentage change of 40.84%, 60.65%, 7.21% and 0.77%, respectively (Table 2). During the nine years, the incidence rate of PTB were relatively higher in the northwestern and southwestern China comparing to other five regions of mainland China (Fig. 6A). The incidence rate of pertussis showed a rebound in most provinces, especially in Guangdong, Fujian, Chongqing and Hunan from 2015 to 2018, and kept stable in three provinces of northeastern China (Table 2, Fig. 6B). Measles was rare in most provinces but showed a rebound from 2014 to 2016 in some provinces (Fig. 6C). By comparing to 2010, three provinces, Yunnan, Hainan, and Fujian, showed increases in the incidence rate of measles in 2018, while the whole country showed decrease trend (Table 2). Seasonal influenza was prevalent throughout the country, especially in southern, central, eastern and northern China in recent years (Fig. 6D). The incidence rate of seasonal influenza increased in 29 provinces, with the greatest increase in Beijing, Hubei, Guangdong and Zhejiang (Table 2). The incidence rate of mumps decreased in 16 out of 31 provinces, and the largest percentage change was 79.34% and found in Ningxia, while increased in 15 provinces with the greatest change found in Tibet (107.38%), followed by Hunan (46.36%) and Qinghai (46.58%) (Table 2). The mumps was prevalent in the whole country before 2014, and incidence rate of mumps was relatively higher in southern and central China since 2014 (Fig. 6E). The incidence rate of rubella kept low level in the whole country since 2013 (Fig. 6F). By comparing to 2010, the incidence rate of rubella decreased in 29 out of 31 provinces, while increased in Hainan (324.94%) and Guangxi (9.95%) (Table 2).
We also analyzed the spatial distributions of the mortalities for PTB and seasonal influenza (Fig. 7). The mortality of PTB decreased in 21 provinces with the greatest decrease in Beijing (76.18%), while increased in 10 provinces, especially in Xinjiang with an increase of 215.58%. The mortality of PTB kept relatively lower in eastern, northeastern and central China during the nine years (Fig. 7A). The reported deaths of seasonal influenza scattered and there was no death in some provinces during the nine years (Fig. 7B).