Epidemiological features and spatial clusters of hand, foot, and mouth disease in Qinghai Province, China, 2009-2015

Abstract

Background: Hand, Foot, and Mouth Disease (HFMD) is most frequently caused by Enterovirus71 (EV-A71) or Coxsackie virus A16 (CV-A16), infants and young children are at greatest risk. Describing the epidemiology of HFMD can help develop and better target interventions, including the use of pediatric EV-A71 vaccination.

Methods: We obtained data from the national surveillance system for HFMD cases with onset dates from 2009 to 2015. We defined probable cases as patient with skin papular or vesicular rashes on the hands, feet, mouth, or buttocks and confirmed cases as patients with the above symptoms along with laboratory-based enterovirus detection. We generated overall and age-specific annual incidence rates and described the temporal variability and seasonality of HFMD in Qinghai Province. We identified spatial clustering of HFMD incidence at the county level using the Local Indicator of Spatial Associationand an alpha level of 0.05.

Results: During the study period, 14,480 HFMD probable or confirmed cases were reported in Qinghai Province. Of the 2158 (14.9%) with laboratory confirmation, 924 (42.6%) were caused by CV-A16 and 830 (38.2%) were caused by EV-A71. The majority (89%) of all case-patients were ≤ 5 years of age and male (61.5%). The overall mean annual HFMD incidence rate was 36.4 cases per 100,000 populations, while the incidence rate for children ≤5 years of age was 379.5 cases per 100,000. Case reports peaked during the months of May through July. HFMD was predominantly caused by EV-A71, except in 2010 and 2014 when CV-A16 was the predominant causative agent. High incidence rates of HFMD were clustered (Moran's I = 0.59, P < 0.05) in the eastern region of the province.

Conclusion: HFMD remains an important cause of childhood disease in Qinghai Province, occurring in an acyclical pattern of increased incidence, primarily due to CV-A16 circulation every three years. Incidence is also seasonal and tends to spatially cluster in the eastern region of the province. Since approximately 40% of confirmed HFMD cases were due to EV-A71, EV-A71 vaccination is likely to have a positive impact on the HFMD disease burden. Routine analysis of local surveillance data is crucial for describing disease occurrence and changes in etiology.

Keywords: Cyclical pattern; HFMD; Qinghai Province; Spatial clusters.

Fig. 1

Map of Qinghai Province, China by climate zone and prefecture

Fig. 2

Reported cases Hand Foot and Mouth Disease, Qinghai, China, 2009–2015, by etiology and year (n = 14,480). (a) Distribution of Hand, Foot, and Mouth Disease by case definition (probable and confirmed) and etiology of laboratory-confirmed cases by year. (b) Distribution of Hand, Foot, and Mouth Disease of laboratory-confirmed cases by year. (c) Distribution of CV-A16 and EV-A71 etiology among laboratory-confirmed cases and overall incidence rate of HFMD by year

Fig. 3

Heatmap of reported cases of Hand, Foot, and Mouth Disease by prefecture and year, Qinghai Province, China, 2009–2015 (n = 14,480). (a) Time series of monthly reported cases of HFMD, standardized by the number of annual cases. (b) Seasonal distribution of cases of HFMD, standardized by range (maximum and minimum) normalization method from 2009 to 2015. For (A) and (b), prefectures were ordered top to bottom by latitude from north to south

Fig. 4

Annual and mean seven-year county-level incidence rates of HFMD for children 0 to 5 years of age, Qinghai Province, China, 2009–2015

Fig. 5

Statistically significant county-level high incidence and low incidence spatial clusters of Hand, Food, and Mouth Disease, for children 0 to 5 years of age, Qinghai Province, 2009–2015. Clusters detected using the Local Indicator for Spatial Autocorrelation (LISA) in GeoDa statistical software (http://geodacenter.github.io/download.html)