Trends in overall respiratory infectious diseases
From 2004 to 2018, a total of 23,444,640 cases and 45,291 deaths caused by seven respiratory infectious diseases were recorded in China, accounting for 25.96% and 19.53% of 44 notifiable infectious cases and deaths in China, respectively. The yearly average cases and deaths were 1,562,976 and 3,019, resulting in mean age-standardized incidence and mortality of 115.87/100,000 and 0.23/100,000, respectively. The incidence and mortality of 100,000 in 2018 were significantly higher than those in 2004, with an increase of 31.36% and 87.30%, respectively. Additionally, the AAPC of age-adjusted incidence was 0.23 across the whole of China during 2004-2018; however, the AAPC of age-adjusted mortality was -2.11. The overall case-fatality ratio (CFR) was 1.93 per 1,000, and the highest yearly CFR was for meningitis (91.08 per 1,000) (Tables 1 and 2). Of the seven respiratory diseases, pulmonary tuberculosis (PTB; 63.20%), mumps (18.21%), and influenza (12.49%) accounted for the majority. In contrast, PTB (93.76%), influenza (2.84%), and meningitis (2.21%) had the highest mortality rates (Figure 1).
Incidence and mortality of seven respiratory infectious diseases differed by age. The incidence and mortality of PTB was the highest in adolescents aged≥15 years (except in 2009). As for incidence, mumps was more prevalent in children aged 3 to 14 years, except in 2016 to 2018. Measles was the most common infection in children aged <1 year between 2004 and 2015 (except 2012); however, the leading disease was influenza between 2016 and 2018. Measles, influenza, and mumps were the most prevalent in children aged <3 years and varied with the particular year. For mortality, measles was the most common cause of death in those aged <14 years before 2008, while between 2008 and 2018, the top four diseases with the highest mortality were measles, meningitis, influenza and PTB (Figure 2). The detailed trend of seven respiratory diseases can be seen in Supplementary Figure 2-6.
Exposure–lag–response associations between air pollutants and respiratory infectious diseases
The DLNM model qualitatively showed that the risk of respiratory infectious diseases was increased when the PM10 concentration was higher than 100 µg/m3. In addition, the relative risk (RR) values increased at month lags 6–10, 2–8, 0–4, 0–12, 0–8, 0–6 for influenza, measle, mumps, pertussis, meningitis and PTB, respectively (Figure 3). The cumulative exposure-response curve of PM10 on mumps, meningitis and PTB showed J-shaped (Figure 4).
The risk of influenza, pertussis and rubella increases at month lags 3–9, 6–12 and 11–12, respectively when SO2 was higher than 50 µg/m3 (Supplementary Figure 7). However, low SO2 concentration (below the median, 17µg/m3) can slightly increase the risk for measle, meningitis, PTB and rubella (Supplementary Figure 8).
The risk of influenza, pertussis, mumps, meningitis and PTB increased at month lags 1–9, 0–4, 1–5 and 1–8, 0–3 respectively when CO was higher than 1.5 µg/m3 (Supplementary Figure 9). Additionally, high CO concentration (above the median) had a stronger effect on rubella which might increase risk significantly (RR > 1, Supplementary Figure 10).
The risk of meningitis, mumps, pertussis and PTB increases at month lags 0–2, 0–1, 0–9 and 0–1 respectively when NO2 was higher than 40 µg/m3 (Supplementary Figure 11). We also found with the protective effect for influenza at the NO2 concentration above the median (32 µg/m3), while it had statistically significant risk effects (RR > 1) at the NO2 concentration below the median (Supplementary Figure 12).
The protective effect for influenza, mumps and rubella at the O3 concentration above the median (84 µg/m3, Supplementary Figure 13), while it had statistically significant risk effects (RR > 1) at the O3 concentration below the median (Supplementary Figure 14).
Exposure–lag–response associations between meteorological factors and respiratory infectious diseases
The risk of mumps and measle increased when RH > 70% (the median) and > 86%, respectively, while the risk of increased of rubella when RH < 35% (Figure 4). The higher risks of PTB were found at lags 0–2 when mean temperature was between -20°C and -5°C (Supplementary Figure 15), and a U-shaped relationship was consistently found between mean temperature and PTB (Supplementary Figure 16). The RRs of influenza and measle were the highest at lags 0–0.3 when rainfall > 500mm (Supplementary Figure 17). The risk of influenza and pertussis increased significantly when the rainfall less than 20mm and 50mm, respectively. Moreover, the cumulative exposure-response curve of rainfall on measle and rubella showed N-shaped (Supplementary Figure 18).
For wind speed, lower wind speed increased the risk of influenza (Supplementary Figure 19); however, the wind speed had statistically significant risk effects on mumps (RR > 1) at wind speed > 3.8 m/s approximately (Supplementary Figure 20). In addition, both lower sunshine hour and higher sunshine hour were increased the risk of influenza, measle, meningitis, mumps and PTB (Supplementary Figure 21). Two U-shaped relationship was consistently found between measle and mumps and sunshine hour (Supplementary Figure 22). The sunshine hour less than 80 hours was significantly increased the risk of PTB (1 < RR < 3.2).