Nonlinear and Interactive Effects of Temperature and Humidity on Childhood Hand, Foot and Mouth Disease in Hefei, China.

Background: Hand, foot and mouth disease (HFMD) is one of the major infectious diseases among children and remains a health threat, especially among Asian countries. Many epidemiologic studies suggested significant association of air temperature and humidity with childhood HFMD; however, evidence on the temperature effects on childhood HFMD in temperate cities is limited, and the interactive effects of temperature and humidity have not been studied yet. Methods: Daily counts of HFMD in children younger than 15 years of age and daily meteorologic variables during 2010 to 2012 were obtained in Hefei, China. A distributed lag nonlinear model was applied to estimate the potential nonlinear association between temperature and childhood HFMD. The interactive effects between temperature and humidity on childhood HFMD were also investigated. Results: Temperature rise was associated with higher risk of childhood HFMD. Within the incubation period of HFMD, temperature rise appeared to have the acute effects on childhood HFMD, and a 5 degrees C increase of temperature at lag 0-6 days was associated with 24.8% (95% confidence interval: 11.94%-39.10%) increase of childhood HFMD. Females and children of 0-4 years of agewere more vulnerable to temperature rise. Notably, there were obvious combined effects between temperature and humidity on childhood HFMD-the risk of childhood HFMD elevated at higher temperature and humidity level. Conclusions: This study provides evidence that temperature and humidity may jointly affect childhood HFMD, and such interactive impact needs to be considered when evaluating the temperature-childhood HFMD relationship.