[Epidemiological analysis on severe fever with thrombocytopenia syndrome under the national surveillance data from 2011 to 2014, China]

Abstract

Objective: To analyze the epidemiological features and surveillance management programs on severe fever with thrombocytopenia syndrome (SFTS) in China from 2011 to 2014.

Methods: The analysis of epidemiological characteristics and surveillance management programs was based on the annual reporting data collected from the National Disease Reporting Information System while the description of cluster incidents was based on those reports collected from the Public Health Emergency Information Management System (PHEIMS). Association between age groups and fatality rate was tested under the Cochran-Armitage Trend Test. The difference of fatality rates between differing groups was analyzed, using the chi-square test, with statistical significance on α = 0.05.

Results: Between 2011 and 2014, 5 352 suspected, probable and lab-confirmed cases of SFTS were reported in 23 provinces, of which 16 provinces reported 2 750 lab-confirmed cases with a fatality of 7.9%, accounting for 51.4% of all the cases, nation-wide. Henan, Shandong, Hubei, Anhui, Liaoning, Zhejiang and Jiangsu reported 99.3% of those lab-confirmed cases. The period between April and October appeared the epidemic season, with its peak from May to July. Most cases were farmers, accounted for 88.3% of the lab-confirmed cases. People at the age between 50-74 occupied 67.6% of all the cases. Fatality of the disease continually increased from 3.7% in the age group 40-44 to 13.5% in the age group older than 80. Fatality rates appeared statistically different between the groups with or without misdiagnosis, with OR as 3.06 (95% CI: 1.61-5.90). Secondary cases of the cluster incidents were most likely to result from contacting the blood of the index cases.

Conclusion: Number of reported SFTS cases showed a rising trend in China. Henan, Hubei, Anhui, Shandong and Liaoning provinces appeared at high risk of the disease. Geographical distribution of the SFTS cases' seemed highly sporadic, with May to July being the peak season. Farmers and elderly were considered as high risk population. Occasionally, cluster incidents might be seen, as the result of contacting the blood of cases or corpses. Being at older age and misdiagnosis seemed to be risk factors for fatality.