Dual Seasonal Patterns for Influenza, China

EID Journal Home > Volume 16, Number 4–April 2010

Volume 16, Number 4–April 2010
Letter
Dual Seasonal Patterns for Influenza, China
Yue-Long Shu,1 Li-Qun Fang,1 Sake J. de Vlas, Yan Gao, Jan Hendrik Richardus, and Wu-Chun Cao1
Author affilations: Chinese Center for Disease Control and Prevention, Beijing, People's Republic of China (Y.L. Shu, Y. Gao); Beijing Institute of Microbiology and Epidemiology, Beijing (L.-Q. Fang); University Medical Center Rotterdam, Rotterdam, the Netherlands (S.J. de Vlas, J.H. Richardus); and State Key Laboratory of Pathogen and Biosecurity, Beijing (W.-C. Cao)

Suggested citation for this article

To the Editor: Since 2000, the People's Republic of China has had a nationwide surveillance network for influenza, which as of 2005 has been reported on the Chinese Center for Disease Control and Prevention website (www.cnic.org.cn/ch). This surveillance has shown a remarkable dual pattern of seasonal influenza on mainland China. Whereas a regular winter pattern is noted for northern China (similar to that in most parts of the Northern Hemisphere), the pattern in southern China differs. In southern China, influenza is prevalent throughout the year; it has a clear peak in the summer and a less pronounced peak in the winter. Because this dual seasonal pattern of influenza has not been reported outside China and is relevant to pandemic (H1N1) 2009, we describe surveillance data for rates of consultation for influenza-like illness (ILI) and influenza subtypes in patients with ILI. We emphasize the spread of influenza from southern to northern China.

Before it was extended in June 2009, the National Influenza Surveillance Network had been composed of 63 influenza laboratories and 197 sentinel hospitals across 31 provinces of mainland China. In 13 of 16 northern provinces, surveillance began from the week including October 1 and ended in the week including March 31 of the following year. In the 3 northern provincial areas of Liaoning, Tianjin, and Gansu and in all southern provinces, surveillance was conducted throughout the year. Data consisted of information about ILI cases and virus subtypes. The sentinel hospitals defined ILI cases according to World Health Organization criteria: sudden onset of fever >38°C, cough or sore throat, and absence of other diagnoses (1). The number of ILI cases and the total number of outpatients at the sites (ILI consultation rate) were recorded each day and reported to the National Influenza Surveillance Information System each week.

Sentinel hospitals were required to collect 5–15 nasopharyngeal swabs each week from ILI patients who had not taken antiviral drugs and who had fever (>38°C) for no longer than 3 days. The swabs were sent to the corresponding influenza laboratories for virus isolation and identification; results were reported to the National Influenza Surveillance Information System within 24 hours.

Suggested Citation for this Article
Shu Y-L, Fang L-Q, de Vlas SJ, Gao Y, Richardus JH, Cao W-C. Dual seasonal patterns for influenza, China [letter]. Emerg Infect Dis [serial on the Internet]. 2010 Apr [date cited]. http://www.cdc.gov/EID/content/16/4/725.htm

DOI: 10.3201/eid1604.091578

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