Weather effects on hand, foot, and mouth disease at individual level: a case-crossover study.
BACKGROUND
Hand, foot, and mouth disease (HFMD) raises an urgent public health issue in the Asia-Pacific region, especially in China. The associations between weather factors and HFMD have been widely studied but with inconsistent results. Moreover, previous studies utilizing ecological design could not rule out the bias of exposure misclassification and unobserved confounders.


METHODS
We used case-crossover analysis to assess the associations of weather factors on HFMD. Individual HFMD cases from 2009 to 2012 in Guangdong were collected and cases located within 10 km of the meteorological monitoring sites were included. Lag effects were examined through the previous 7 days. In addition, we explored the variability by changing the distance within 20 km and 30 km.


RESULTS
We observed associations between HFMD and weather factors, including temperature and relative humidity. An approximately U-shaped relationship was observed for the associations of temperature on HFMD across the same day and the previous 7 days, while an approximately exponential-shaped was seen for relative humidity. Statistically significant increases in rates of HFMD were associated with each 10-unit increases in temperature [Excess rate (ER): 7.7%; 95% Confidence Interval (CI): 3.9, 11.7%] and relative humidity (ER: 1.9%; 95% CI: 0.7, 3.0%) on lag days 0-6, when assessing within 10 km of the monitoring sites. Potential thresholds for temperature (30.0 °C) and relative humidity (70.3%) detected showed associations with HFMD. The associations remained robust for 20 km and 30 km.


CONCLUSIONS
Our study found that temperature and relative humidity are significantly associated with the increased rates of HFMD. Thresholds and lag effects were observed between weather factors and HFMD. Our findings are useful for planning on targeted prevention and control of HFMD.
['Du|Zhicheng|Z|', 'Lin|Shao|S|', 'Marks|Tia|T|', 'Zhang|Wangjian|W|', 'Deng|Te|T|', 'Yu|Shicheng|S|', 'Hao|Yuantao|Y|http://orcid.org/0000-0002-1155-8443']
D000293:Adolescent D002648:Child D002675:Child, Preschool D002681:China D018592:Cross-Over Studies D004463:Ecology D019550:Environmental Medicine D005260:Female D006232:Hand, Foot and Mouth Disease D006801:Humans D006813:Humidity D015994:Incidence D007223:Infant D007231:Infant, Newborn D016015:Logistic Models D008297:Male D013696:Temperature D014887:Weather
Weather effect Hand, foot, and mouth disease Case-crossover