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. 2016 Aug 1;10(8):e0004875.
doi: 10.1371/journal.pntd.0004875. eCollection 2016 Aug.

Spatiotemporal Dynamics of Scrub Typhus Transmission in Mainland China, 2006-2014

Affiliations

Spatiotemporal Dynamics of Scrub Typhus Transmission in Mainland China, 2006-2014

Yi-Cheng Wu et al. PLoS Negl Trop Dis. .

Abstract

Background: Scrub typhus is endemic in the Asia-Pacific region including China, and the number of reported cases has increased dramatically in the past decade. However, the spatial-temporal dynamics and the potential risk factors in transmission of scrub typhus in mainland China have yet to be characterized.

Objective: This study aims to explore the spatiotemporal dynamics of reported scrub typhus cases in mainland China between January 2006 and December 2014, to detect the location of high risk spatiotemporal clusters of scrub typhus cases, and identify the potential risk factors affecting the re-emergence of the disease.

Method: Monthly cases of scrub typhus reported at the county level between 2006 and 2014 were obtained from the Chinese Center for Diseases Control and Prevention. Time-series analyses, spatiotemporal cluster analyses, and spatial scan statistics were used to explore the characteristics of the scrub typhus incidence. To explore the association between scrub typhus incidence and environmental variables panel Poisson regression analysis was conducted.

Results: During the time period between 2006 and 2014 a total of 54,558 scrub typhus cases were reported in mainland China, which grew exponentially. The majority of cases were reported each year between July and November, with peak incidence during October every year. The spatiotemporal dynamics of scrub typhus varied over the study period with high-risk clusters identified in southwest, southern, and middle-eastern part of China. Scrub typhus incidence was positively correlated with the percentage of shrub and meteorological variables including temperature and precipitation.

Conclusions: The results of this study demonstrate areas in China that could be targeted with public health interventions to mitigate the growing threat of scrub typhus in the country.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Temporal distribution of scrub typhus cases from 2006 to 2014 in mainland China.
The temporal distributions of reported scrub typhus cases in mainland China are presented as the monthly number of cases (blue line) and cumulative cases (gray spikes) in panel A and the total number of cases reported per year (blue dots) fit with an exponential growth function (black line) in panel B.
Fig 2
Fig 2. Seasonal patterns in reported scrub typhus cases from 2006 to 2014 in mainland China.
The seasonal patterns of reported scrub typhus cases in mainland China are presented as the average number of cases reported by month (blue dots) and the incidence rate ratios (IRR) with 95% confidence intervals for the IRR (dashed and dotted lines) derived from a categorical Poisson regression models for the number of reported cases per month, with all months compared to the number of cases reported in January of each year in panel A. The seasonal patterns as determined by monthly autocorrelation between the number of reported cases for each month is presented using time lags between 0 and 60 months in panel B.
Fig 3
Fig 3. Yearly Local Indicators of Spatial Association (LISA) cluster maps for scrub typhus incidence in mainland China, 2006–2014.
LISA spatial cluster map shows the center of the cluster in color. H-H indicates a statistically significant cluster of high scrub typhus incidence values; H-L represents high scrub typhus incidence values surrounded with low incidence values; L-H represents low scrub typhus incidence values surrounded with high incidence values.
Fig 4
Fig 4. Yearly spatiotemporal clusters overlay with annual incidence of scrub typhus in mainland China, 2006–2014.
Yearly spatiotemporal clusters were detected using a circular scan window with the maximum spatial size of 5% of the population at risk and a maximum temporal size of 10% of the study period.
Fig 5
Fig 5. Spatiotemporal clusters overlay with annual average incidence of scrub typhus across the period of 2006–2014 in mainland China.

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