Burden and trends of infectious disease mortality attributed to air pollution, UWSH, and non-optimal temperature from 1990 to 2019

In 2019, global infectious disease deaths attributed to environmental risk factors reached a staggering 2,556,992, with contributions from air pollution, UWSH, and non-optimal temperature of 763,291, 1,656,887, and 245,814 deaths, respectively. The predominant cause of infectious disease deaths associated with air pollution was respiratory infections, contributing to 749,254 fatalities globally in 2019 (95% UI, 573,848 to 959,290). UWSH primarily resulted in deaths from enteric infections, while non-optimal temperature mainly caused respiratory infections, with 1,386,769 (95% UI, 978,063 to 2,009,500) and 245,814 (95% UI, 174,760 to 342,302) deaths, respectively, in 2019.

Examining different SDI regions in 2019, the highest number of infectious disease deaths attributed to air pollution and UWSH occurred in the Low SDI region, with 330,074 (95% UI, 250,942 to 423,208) respiratory infections attributed to air pollution, 6,546 (95% UI, 5,096 to 8,419) enteric infections attributed to air pollution, 2,529 (95% UI, 1,962 to 3,317) deaths from other infectious diseases attributed to air pollution, 640,329 (95% UI, 480,412 to 858,264) enteric infections attributed to UWSH, and 130,090 (95% UI, 58,429 to 200,590) respiratory infections attributed to UWSH. However, in the case of respiratory infections attributed to non-optimal temperatures, the highest death toll was observed in High SDI regions, with 69,216 (95% UI, 51,479 to 88,585) deaths in 2019 (Table 1).

Table 1 Burden and trends between 1990 and 2019 of infectious disease mortality attributed to air pollution, UWSH, and non-optimal temperature globally and in SDI regions

On a global scale, enteric infections, attributed to UWSH, were responsible for the highest number of deaths from 1990 to 2019, ranging from 52.01% to 54.67%. This trend persisted in Middle, Low-middle, and Low SDI regions, where enteric infections attributed to UWSH constituted 44.88% to 49.03%, 59.35% to 61.57%, and 55.10% to 56.89% of all deaths, respectively, from 1990 to 2019. Conversely, in the High-middle SDI region, respiratory infections attributed to air pollution dominated deaths from 1990 to 2015 (34.65% to 38.30%). Subsequently, respiratory infections attributed to non-optimal temperature became the primary cause of deaths from 2016 to 2019, accounting for over 37%. Moreover, in the High SDI region, respiratory infections attributed to non-optimal temperature constituted more than 60% of deaths from 1990 to 2019 (Fig. 1).

Fig. 1

Proportions of deaths of infectious diseases attributed to air pollution, UWSH, and non-optimal temperature from 1990 to 2019, globally and by SDI regions. SDI, Socio-Demographic Index; UWSH, unsafe water, sanitation, and handwashing

Among the three categories of infectious diseases tied to air pollution, respiratory infections had the highest ASMR both in 1990 (27.71 per 100,000 population, 95% UI, 21.66 to 34.76) and 2019 (10.38 per 100,000 population, 95% UI, 7.89 to 13.28). UWSH and non-optimal temperature primarily resulted in enteric infections and respiratory infections, with ASMRs of 18.94 (95% UI, 13.59 to 26.96) and 3.41 (95% UI, 2.42 to 4.77) per 100,000 population in 2019 (Table 1).

All infectious diseases attributed to air pollution, UWSH, and non-optimal temperature exhibited declining trends in ASMR globally from 1990 to 2019, with the most rapid decrease observed in enteric infections attributed to air pollution (EAPC = -5.20%, 95% CI, -5.52% to -4.78%). This category decreased from 0.74 (95% CI, 0.52 to 0.93) per 100,000 population in 1990 to 0.16 (95% CI, 0.13 to 0.20) per 100,000 population in 2019. Following closely were enteric infections attributed to UWSH, exhibiting an average annual decrease of 3.73% (95% CI, 3.60% to 3.85%), declining from 8.44 (95% UI, 3.63 to 12.97) per 100,000 in 1990 to 3.74 (95% UI, 1.66 to 5.83) per 100,000 in 2019.

Analyzing within different SDI regions, the highest ASMRs of infectious diseases associated with air pollution, UWSH, and non-optimal temperature were consistently observed in Low SDI regions, in both 1990 and 2019. Across all SDI regions, the ASMRs of infectious diseases attributed to air pollution, UWSH, and non-optimal temperature demonstrated declining patterns from 1990 to 2019 (all p < 0.05) (Fig. 2).

Fig. 2

Trends of ASMRs of infectious diseases attributed to air pollution, UWSH, and non-optimal temperature from 1990 to 2019, globally and by SDI regions. ASMR, Age-standardized mortality rate; SDI, Socio-Demographic Index; UWSH, unsafe water, sanitation, and handwashing

Age disparities of infectious disease mortality attributed to air pollution, UWSH, and non-optimal temperature

Figure 3 illustrated the global mortality rates of infectious diseases that are attributable to air pollution, UWSH, and non-optimal temperature, in various SDI regions, and across different age groups for the years 1990 and 2019. Notably, air pollution was exclusively linked with deaths from enteric infections and other infectious diseases only in children under the age of 5, with this correlation not being observed in other age groups. The highest mortality rates were observed in the Low SDI region in 2019: 3.83 (95% UI, 2.98 to 4.93) per 100,000 for enteric infections and 1.48 (95% UI, 1.15 to 1.94) per 100,000 for other infectious diseases.

Fig. 3

Mortality of infectious diseases attributed to air pollution, UWSH, and non-optimal temperature in different age groups, in 1990 and 2019, globally and by SDI regions. SDI, Socio-Demographic Index; UWSH, unsafe water, sanitation, and handwashing

In cases of respiratory infections attributed to air pollution, non-optimal temperature, UWSH, and enteric infections due to UWSH, both children under five years old and the elderly were significantly impacted. In 2019, the global mortality rates for these conditions in children under 5 were 45.90 (95% UI, 33.50 to 60.41), 8.69 (95% UI, 4.90 to 16.17), 17.24 (95% UI, 7.78 to 27.39), and 71.02 (95% UI, 54.77 to 92.29) per 100,000 population, respectively. In individuals aged over 80, the rates were 101.96 (95% UI, 74.03 to 135.37), 66.46 (95% UI, 49.13 to 87.47), 33.08 (95% UI, 14.11 to 52.85), and 202.05 (95% UI, 116.59 to 330.79) per 100,000 population, respectively. Low SDI regions consistently reported the highest mortality rates across all age groups.

From 1990 to 2019, most age brackets showed a downward trend in mortality rates for respiratory infections resulting from air pollution, non-optimal temperature, UWSH, along with enteric infections attributed to UWSH. Children under the age of 5 exhibited the most significant decline in all diseases and SDI regions. However, in High SDI region, there were increasing trends in mortality rates for enteric infections attributed to UWSH among individuals aged 65–69 (EAPC = 0.38%, 95% CI, 0.02% to 0.75%), 75–79 (EAPC = 0.61%, 95% CI, 0.02% to 1.20%), and over 80 years (EAPC = 1.81%, 95% CI, 1.20% to 2.42%) (Fig. 4).

Fig. 4

EAPC of mortality of infectious diseases attributed to air pollution, UWSH, and non-optimal temperature in different age groups, from 1990 to 2019, globally and by SDI regions. EAPC, Estimated Annual Percentage Change; SDI, Socio-Demographic Index; UWSH, unsafe water, sanitation, and handwashing

PAF of environmental risk factors for infectious disease mortality

On a global scale, diarrheal diseases emerged as the predominant cause of death among infectious diseases linked to environmental risk factors, with lower respiratory infections following closely. The primary contributors to diarrheal disease deaths were unsafe sanitation, an insecure water source, and lack of access to handwashing facilities. Ambient particulate matter pollution and household air pollution from solid fuel played subsidiary roles in a minority of diarrheal disease deaths. Lower respiratory infections were attributed to factors such as the absence of handwashing facilities, ambient particulate matter pollution, household air pollution from solid fuel, high temperature, and low temperature. These conditions persisted across Middle, Low-middle, and Low SDI regions. However, in High and High-middle SDI regions, lower respiratory infections accounted for the majority of infectious disease deaths (Fig. 5).

Fig. 5

Contribution Proportion of air pollution, UWSH, and non-optimal temperature to Infectious Disease Mortality, in 1990 and 2019, globally and by SDI regions. SDI, Socio-Demographic Index

Examining the global scenario, for deaths related to diarrheal diseases, the highest PAF in 2019 was associated with an unsafe water source (PAF = 80.17%), followed by unsafe sanitation (49.31%), and lack of access to handwashing facilities (23.32%). Concerning lower respiratory infections, household air pollution stemming from solid fuels had the highest PAF (16.96% in 2019), followed by ambient particulate matter pollution (13.09%), and the absence of handwashing facilities (10.83%). Moreover, the PAF of household air pollution played a central role in lower respiratory infections across Middle, Low-middle, and Low SDI regions. In contrast, High and High-middle SDI regions were primarily impacted by low temperature (17.43% in High SDI region and 11.77% in High-middle SDI region, in 2019). Notably, the PAF of ambient particulate matter pollution for lower respiratory infections exhibited an upward trend from 1990 to 2019. This trend was consistent in Middle (from 13.10% to 16.77%), Low-middle (from 7.62% to 18.16%), and Low (from 4.79% to 10.33%) SDI regions. Similarly, the PAF of high temperature for lower respiratory infections also exhibited an upward trajectory in these three SDI regions, rising from 2.50% to 2.61%, 5.12% to 5.58%, and 5.09% to 5.41%, from 1990 to 2019 respectively (Table 2).

Table 2 PAF of air pollution, UWSH, and non-optimal temperature for infectious disease mortality, in 1990 and 2019, globally and by SDI regionsAssociation between SDI and infectious disease mortality attributed to air pollution, UWSH, and non-optimal temperature in 21 GBD regions

For enteric infections attributed to air pollution and UWSH, as well as other infectious diseases attributed to air pollution, and respiratory infections attributed to air pollution and UWSH, there was a consistent decrease in the ASMR of infectious diseases with the rise in SDI. The second order polynomial regression revealed a strong correlation (R-squared ranging from 0.78 to 0.91). Nonetheless, for respiratory infections triggered by non-optimal temperatures, the association between ASMR and SDI lacked statistical significance (R-squared of the second order polynomial regression was lower than 0.1).

On analyzing particular diseases, the Caribbean displayed the highest ASMR for enteric infections and other infectious diseases resulting from air pollution, surpassing other regions with similar SDIs. In contrast, Central, Western, and Southern Sub-Saharan Africa reported the highest ASMR for respiratory infections attributed to air pollution and UWSH compared to other regions with comparable SDIs. Additionally, South Asia recorded the highest ASMR for enteric infections attributed to UWSH when compared to regions with similar SDIs (Fig. 6).

Fig. 6

The correlation between ASMR of infectious diseases attributed to air pollution, UWSH, and non-optimal temperature and SDI in 21 GBD regions. ASMR, Age-standardized mortality rate; SDI, Socio-Demographic Index; GBD, Global Burden of Disease Study; UWSH, unsafe water, sanitation, and handwashing