Effects of relative humidity on childhood hand, foot, and mouth disease reinfection in Hefei, China
Graphical abstract
Introduction
Hand, foot, and mouth disease (HFMD) is a viral illness predominantly caused by Coxsackievirus A16 (CA16) and Enterovirus 71 (EV71) (Li et al., 2016) and may result in severe and fatal events (Luo et al., 2016), mostly affecting young children and infants (Koh et al., 2016). The symptoms of HFMD are fever, anorexia, headache, and small vesicular lesions or ulcers appearing in hands, feet, and other body parts. This disease can also lead to severe complications, such as myocarditis, pulmonary edema, and meningitis (Abedi et al., 2015). Viruses are transmitted from person to person and result in individual infection due to close contact with the secretions and contaminants of infected persons (Phyu et al., 2017). To the best of our knowledge, specific antiviral therapy could not be used for EV until now (Abzug, 2014).
Since the 1970s, HFMD outbreaks have been reported in several countries, mainly in the Western Pacific region, including Vietnam (Nguyen et al., 2017), Malaysia (NikNadia et al., 2016), and Singapore (Ang et al., 2015). Europe and America also suffered from the epidemic of HFMD. In 2015, France and Texas were attacked by CA16, which resulted in the infection of many children (Banta et al., 2016; Mirand et al., 2016). China has become one of the most affected areas and classified this disease as a Category C infectious disease in 2008. After a natural infection, antibodies protect the body from infections by the corresponding virus subtype, but these antibodies lack cross-protection against diverse subtypes (Huang et al., 2012). Chen et al., (2016) and Xie et al., (2014) found that HFMD reinfection rate is 2.02% and 3.15%, respectively. Those severe conditions prompt us to identify the risk factors of HFMD reinfection and adopt timely and effective measures to alleviate the burden of this disease.
Previous articles have presented evidence of the relationship between meteorological factors and HFMD. Nguyen et al., (2017) observed that the HFMD rate increased by 5.6% for every 1 °C increase in average temperature. A study in Guangdong (Zhang et al., 2016) revealed that sunshine contributed 6.21%–10.36% to HFMD epidemic and wind speed contributed 3.84%–11.37%. Wu et al., (2017) revealed a significant relationship between rainfall and HFMD. Meanwhile, the association between different climate factors, especially relative humidity, and HFMD could be inconsistent. Phung et al., (2018) found that HFMD increased by 3.1% for every 1% increase in monthly humidity above 76%. Kim et al., (2016) conducted a study in South Korea and revealed that HFMD rate decreased by 1.5% when relative humidity above 65% increased by 1%. In addition, in a research conducted in Huainan, no relationship was observed between humidity and HFMD (Zhao et al., 2017). Moreover, no study has examined the correlation between HFMD reinfection and relative humidity. Therefore, understanding the relationship between relative humidity and HFMD reinfection may provide insights valuable to the alleviation of the HFMD reinfection epidemic.
Most of existing studies did not consider the delayed effects of meteorological factors on HFMD reinfection, which may have caused the results to be inaccurate (Guo et al., 2016; Sumi et al., 2017; Xu and Xiao, 2017). Distributed lag nonlinear model (DLNM) was developed for the accurate description of the potential nonlinear and lag effects of the association between health outcomes and related factors. DLNM is therefore suitable for the illustration of the delayed effects of relative humidity on HFMD reinfection.
HFMD in Hefei City has worsened, and severe reinfection cases have occurred in recent years. In this study, we analyzed the effects of exposure to relative humidity on HFMD reinfection in Hefei City from 2011 to 2016. The results of this study will provide scientific evidence for early warning and rapid response.
Section snippets
Research location
This study was conducted in Hefei, which is the capital city of Anhui province and located in the east-central part of China (31°52′N, 117°17′E). Hefei City has an area of 11,445.1 km2 and a population of 9.6 million. Hefei features a subtropical monsoon climate with four distinct seasons and mild climate.
Data collection
Daily HFMD reinfection counts between January 1, 2011 and December 31, 2016 were obtained from Hefei Center for Disease Control and Prevention. Clinical diagnosis of HFMD complied with a
Descriptive analysis
The summary statistics for daily data on meteorological variables and childhood HFMD reinfection cases in Hefei during the study period are presented in Table 1. A total of 95,710 HFMD cases were reported in Hefei from 2011 to 2016, and 4873 reinfection cases were reported in children aged 0–11 years. The percentages of total reinfection cases were 65.3% for males and 71.9% for the group including individuals aged <4 years. The daily average number of HFMD reinfection cases was 2.2 (range: 0–15).
Discussion
Over the years, HFMD outbreaks have been frequently reported worldwide, particularly in the Asia-Pacific region (Tao et al., 2017; Wang et al., 2014). As a viral disease caused by different virus subtypes, HFMD reinfection is common in children because they lack cross immunity (Huang et al., 2013; Xie et al., 2014). Relative humidity has been considered a factor affecting the incidence of numerous diseases, including HFMD (Dong et al., 2016; Shaman et al., 2017; Zhai et al., 2017). Relative
Conclusions
Our study provides strong evidence of the significant relationship between relative humidity and childhood HFMD reinfection. The adverse effects of relative humidity are long term, but those of low relative humidity are more rapid. Female children and children aged ≥4 years are vulnerable to the effect of extremely high relative humidity. Findings from the current study are essential for the development of an early warning system capable of addressing HFMD reinfection epidemic influenced by
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Declarations of interest
None.
Ethical approval
Ethical approval for the analyses showed in this was not sought as the paper is based on deidentified data provided by Hefei CDC for the purposes of secondary analysis research.
Acknowledgments
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. The authors appreciate Hefei Center for Disease Control and Prevention, and Hefei Bureau of Meteorology for providing dataset needed in this study.
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Yuwei Yang and Enqing You contributed equally to this work and should be considered as co-first authors.