A case-control study to identify environmental risk factors for hand, foot, and mouth disease outbreaks in Beijing

A matched case-control study was conducted in Beijing to identify the relative importance of major environmental risk factors for outbreaks of hand, foot, and mouth disease (HFMD). A case was defined as a kindergarten class with at least 1 HFMD outbreak. As a control, a kindergarten class that did not experience an HFMD outbreak was used. To identify potential transmission factors, the control group was divided into 2 subgroups: a sporadic group and an HFMD-negative group. We collected data for 8 environmental factors and basic information of each class. The correlations between the suspected environmental factors and HFMD outbreaks were analyzed. Thirty outbreak classes, 19 sporadic classes, and 30 HFMD-negative classes were enrolled. Class grade, indoor solar radiation, and ultraviolet (UV) radiation revealed significant differences among the 3 groups. After controlling for other factors, UV radiation (adjusted β = -0.42) and class grade (adjusted β = -0.46) as protective factors and temperature (adjusted β = 0.31) as a risk factor were significantly associated with the attack rate by multiple linear regression analysis. Logistic regression analysis showed that the probability of an HFMD outbreak in the lower grade was 6-fold greater than that in the higher grade (P = 0.0380, odds ratio = 0.157, 95% confidence interval = 0.027-0.903). We identified UV radiation and class grade as protective factors that were associated with the epidemic intensity in Beijing. However, more data is needed to evaluate the relationship between these factors and HFMD outbreaks.