An increased risk of acute hemorrhagic conjunctivitis (AHC) is associated with long-term exposure to higher mean temperature, relative humidity (RH) and precipitation, according to findings published in Environmental Research.
A Chinese research team conducted a study to quantify the relationship between the environment and AHC. The researchers retrieved the monthly counts and incidence of AHC, meteorological variables, and air quality in mainland China between 2013 and 2018, and they evaluated exposure risks using multivariate distributed lag nonlinear models.
The study found that 219,599 cases of AHC had been reported in 31 Chinese provinces, with a seasonal increase in the summer. The cases were located predominantly in Southern and Central China. Between 2013 and 2018, AHC incidence increased by 7%, from 2.68 to 2.75 per 100,000 people. The researchers note a moderate, positive correlation between AHC and monthly mean temperature, RH and precipitation. Each unit increment was associated with a relative risk of AHC of 1.058 at 17° C to 32° C at lag 0 months, 1.017 at 65-71%RH at lag 1.4 months, and 1.039 at 4000 mm to 569 mm at lag 2.4 months. However, there was a negative correlation between monthly ambient [nitrogen dioxide] NO2 and AHC.
The researchers explain that, although an increase in enterovirus-related outbreaks in recent years globally, the efforts to identify their underlying mechanism is ongoing.
“Two emerging [enterovirus]-induced infectious diseases, AHC and [hand, foot and mouth disease], mostly occur in warmer, southern parts of China, with a summer peak,” the study notes. “This seasonal and geographical variation suggests that weather risk factors could promote [enterovirus] circulation.”
The study cites possible reasons for this increase as higher ambient temperatures leading to a faster rate of enterovirus, and thus AHC, transmission; the temperature-induced increase of enterovirus’s infectivity spanning a specific range; and the summertime increase in outdoor activity by children, leading to more contamination and thus an increase in AHC transmission.
Study limitations include the inability of the research to infer the effect of individual exposure levels from air pollution and meteorological conditions; its inability to justify causal relationship between air pollution and AHC incidence; its basis on monthly data online; and the possible influence of human behavior such as personal hygiene and masks on the associations observed.
Zhang L, Jiang H, Wang K, et al. Long-term effects of weather condition and air pollution on acute hemorrhagic conjunctivitis in China: A nationalwide surveillance study in China. Environ Res. 2021;201(10):111616. doi:10.1016/j.envres.2021.111616.