The influence of temperature and humidity on the incidence of hand, foot, and mouth disease in Japan
Highlights
► We estimated the relationship of weather variability with pediatric HFMD cases. ► HFMD cases increased with increasing average temperature and relative humidity. ► This increase was most remarkable in children aged less than 10 years. ► Weather factors have a significant influence on the incidence of HFMD infections.
Introduction
Hand, foot, and mouth disease (HFMD) is a common viral infection whose main clinical symptoms include fever, mouth ulcers, and vesicles on the hands, feet, and mouth. Although the infection occurs most frequently in children, adolescents and occasionally adults can also acquire HFMD. In most cases, the disease is mild and self-limiting, but more severe clinical symptoms, including neurological abnormalities such as meningitis, encephalitis, and polio-like paralysis, may occur. HFMD is most frequently caused by coxsackievirus A16 (CA16) and enterovirus 71 (EV71) (Melnick, 1996, Tunnessen, 1992, Chen et al., 2007); however, EV71 is more commonly linked with severe symptoms, including central nervous system disorders, and even fatality resulting from pulmonary edema in a small proportion of children, particularly those aged 5 years and younger (Cohen, 1998).
The incidence of HFMD has been reported to exhibit seasonal variation in a number of different areas. For example, a bimodal seasonal pattern has been detected in the United Kingdom, which is characterized by peaks in HFMD incidence in the summer and late autumn/early winter (Bendig and Fleming, 1996). In Belgium, HFMD infections are typically present throughout the year, showing small peaks in summer and autumn (Druyts-Voets, 1997), while the incidence of HFMD is highest in summer in Taiwan (Chen et al., 2007). In Hong Kong, it has been suggested that the changing epidemiology (an occurrence of winter peak) was due to increase in winter temperature (Ma et al., 2010a). The incidence frequency also appears to be influenced by the infectious agent. For example, when CA16 was the predominant circulating enterovirus in Singapore, a single epidemic peak was observed, whereas two peaks were detected in other epidemic years (Ang et al., 2009). In Malaysia, outbreaks occurred in a cyclical pattern every 3 years involving the co-circulation of CA16 and EV71, with sporadic increases in activity observed between large outbreaks (Podin et al., 2006). The observed seasonality of HFMD suggests that its incidence may be influenced by weather factors and indicates the existence of multiple functional pathways leading to infection and subsequent outbreaks. Despite this speculation, the impact of weather variability on the incidence of HFMD with adjustment for the mutual confounding between weather and other seasonal factors has only been investigated in a limited number of studies.
Here, we examined the possible relationship of temperature and humidity variability with the incidence of pediatric HFMD cases using surveillance data collected in Fukuoka, Japan, from 2000 to 2010.
Section snippets
Data sources
In Fukuoka Prefecture, which is located in the southwest of Japan, the number of HFMD patients is reported on a weekly basis from 120 sentinel medical institutions (Onozuka et al., 2010). HFMD was defined by clinical factors, which included vesicular lesions on hands, feet, mouth (which were often ulcerated), and, frequently, buttocks, in accordance with the Act on Prevention of Infectious Diseases and Medical Care for Patients Suffering Infectious Diseases (Ministry of Health, Labour and
Results
A total of 73,684 (100%) HFMD cases from 2000 to 2010 were included in our analyses, of which 61,736 (83.8%) were in children aged 0–4 years, 10,815 (14.7%) in those aged 5–9 years, 619 (0.8%) in those aged 10–14 years, and 514 (0.7%) in those aged over 15 years. Descriptive statistics for the number of patients based on age and weather variables are summarized in Table 1. From the analysis of the weekly reported number of HFMD cases, the seasonal peak in cases was found to differ from year to
Discussion
Our analysis of the effects of temperature and humidity on the incidence of HFMD in Fukuoka, Japan has yielded several notable findings. After adjustment for potential confounding by seasonal patterns and inter-year variations, we detected that the number of HFMD cases increased with increasing temperature and relative humidity. Notably, this increase was most remarkable in children aged less than 10 years. Our results demonstrate that weather factors have a significant influence on the
Financial support
The study was supported in part by a Grant-in-Aid for Scientific Research from the Ministry of Health, Labour and Welfare, Japan.
Conflict of interest
None declared.
Acknowledgements
We thank the Fukuoka Prefectural Government, Department of Public Health and Medical Affairs, Division of Public Health for their painstaking efforts in infectious disease surveillance in Fukuoka, Japan. The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Fukuoka Prefectural Government.
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