Age patterns and transmission characteristics of hand, foot and mouth disease in China

Abstract

Background: Hand, foot and mouth disease (HFMD) has circulated in China and caused yearly outbreak. To understand the transmission of the disease and to assess the spatial variation in cases reported, we examined age-specific transmission characteristics and reporting rates of HFMD for 31 provinces in mainland China.

Methods: We first analyzed incidence spatial patterns and age-specific incidence patterns using dataset from 2008 to 2012. Transmission characteristics were estimated based on catalytic model. Reporting rates were estimated using a simple mass action model from "Time Series Susceptible Infectious Recovered" (TSIR) modeling.

Results: We found age-specific spatial incidence patterns: age-specific proportions of HFMD cases varied geographically in China; larger case percentage was among children of 3-5 years old in the northern part of China and was among children of 0-2 years old in the southern part of China. Our analysis results revealed that: 1) reporting rates and transmission characteristics including the average age at infection, the force of infection and the basic reproduction number varied geographically in China; 2) patterns of the age-specific force of infection for 30 provinces were similar to that of childhood infections in developed countries; the age group that had the highest infection risk was 3-5 years old in 30 provinces, and 10-14 years old in Tibet; 3) a large difference in HFMD transmission existed between northwest region and southeast region; 4) transmission characteristics determined incidence patterns: the higher the disease transmission in a province, the earlier the annual seasonality started and the more case percentage was among children 0-2 years old and less among 3-5 years old.

Conclusion: Because HFMD has higher transmission than most childhood infections reported, high effective vaccine coverage is needed to substantially reduce HFMD incidence. Control measures before the vaccine implementation should focus on 2-6 years old children in 30 provinces and 10-14 years old children in Tibet.

Keywords: Average age at infection; Force of infection; Hand foot and mouth disease; Reporting rate.

Fig. 1

Incidence of HFMD for 31 provinces in China from May 2008 to December 2012. a Incidence of 31 provinces. Provinces from left to right were ranked by climate zone that the province is in and the latitude of province captical if provinces were in the same climate zone. b Scatter plot of average incidence and population density. Since many studies associate incidence with climate and population density, it is reasonable to include climate zone information and population density into the exhibit of incidence. c Provinces colored according to which climate zones they belong to. The country were divided into northwest and southeast regions

Fig. 2

Heatmaps of age-specific incidence of HFMD for 31 provinced in China from January 2008 to December 2011. a Heatmap of case percentage among 0–2 years old for 31 provinces. b Heatmap of case percentage among 3–5 years old for 31 provinces. c Case percentage among age groups of 0–2 years old (blue line), 3–5 years old (red line) and 6–19 years old (green line) of some selected provinces. Winter and summer vacations are shown in narrow bands. Winter and summer vacation times in China are: 1 month during January or February depending on Chinese lunar new year, and from early July to the end of August

Fig. 3

Age-specific force of HFMD infections at the country level and in 31 provinces in China. a Age-specific force of infection for HFMD in China from 2008 to 2012. b Heatmap of averaged age-specific force of infection for HFMD in 31 provinces from May 2008 to December 2011

Fig. 4

The average age at infection of HFMD in 31 provinces in China from 2008–2011. Figure was generated using Tableau Desktop version 8.3 (http://www.tableau.com/support/releases/8.3)

Fig. 5

The relationship of the average age at infection with case percentage among age groups and timing of seasonality for 31 provinces in Chia from 2008–2011. a Average age at infection vs proportion of incidence. Color of symbols according to climate zone, with filled circles representing case percentage among children of 0–2 years old and open triangle representing case percentage among children of 3–4 years old. Regression lines exclude data of Tibet. b Average age at infection vs starting time of spring seasonality of incidence. Tibet have fall seasonality instead of spring seasonality of incidence, hence it was excluded from the regression line