The Evaluation of Expanded Epidemic Investigations on Dengue Fever Cases in Taiwan between 2009 and 2011

Shu-Kuan Lai1, Jiun-Shian Kuo1, Jhy-Wen Wu2, Ding-Ping Liu3

2013 Vol.29 NO.22

Correspondence Author: Shu-Kuan Lai

  • 1.Division of Acute Infectious Diseases, Centers for Disease Control, Ministry of Health and Welfare
  • 2.Northern Regional Center, Centers for Disease Control, Ministry of Health and Welfare
  • 3.Epidemic Intelligence Center, Centers for Disease Control, Ministry of Health and Welfare


       Dengue fever, with the highest incidence rate of confirmed cases in the last ten years, is the most common acute infectious disease in Taiwan. Annually more than ten thousand people had their samples collected and tested for the dengue virus over the past three years. In order to apply dengue prevention resources more effectively, this article reviewed the expanded epidemic investigations which was conducted between 2009 and 2011. Through the data collected from notificable surveillance system and expanded epidemic investigations, the results indicated the followings: (1) an average of 3,400 suspected dengue cases were reported each year, with 1,500 confirmed cases. Most of cases were reported by medical clinics or hospitals, followed by positive cases through expanded investigations (positive contacts from dengue confirmed cases); (2) an average of 15,700 people were tested for dengue virus each year. Among them, 3,370 (21.5%) came from the surveillance system, while 12,330 (78.5%) came from expanded investigations. The former group had a positive rate of 46%, which was 23 times compared to the later group (2%); (3) less than 1% of dengue confirmed cases collected over 100 contacts through expanded investigations. Although those contacts are 16.4% of the totals, yielded a positive rate of 0.7%, much less than the overall rate of 2%; (4) through expanded investigations, contacts with symptoms were 1.8 to 41.5 times more likely to have a positive result than asymptomatic contacts. This study showed that only 2% of contacts collected from expanded investigations tested positive from 2009 to 2011, while 39.9% of the cases reported by medical clinics or hospitals tested positive. Each positive case through expanded investigations was 20 times more costly than a case identified through reporting source of clinics or hospitals. Because of the high costs associated, expanded epidemic investigations should be conducted on people who have dengue-like symptoms, or possible dengue clusters, or who have travelled to epidemic areas, for the best results. Large-scaled mass investigations should be discouraged during outbreaks.