中国2001～2003年流行性感冒流行特征分析

Epidemiologic characteristics of influenza in China, from 2001 to 2003

目的 分析中国2001～2003年流行性感冒(流感)流行特征。方法 收集2001～2003年全国流感监测网流感样病例(ILI)监测资料,流感病毒分离与鉴定结果以及爆发疫情信息进行分析。结果 2001～2003年,中国北方地区流感流行高峰为12月或次年1月,南方地区则为4、5、7、8月和11、12月。北方、南方地区ILI就诊百分比基线值分别为13.68％、13.08％。ILI的年龄构成与流感流行季节类型有关。流感爆发疫情以5月份最多(32％),一般在6月前后流感疫情毒株类型发生改变。结论 中国南、北方流感流行特征有所不同。南方地区可能存在春季流行高峰,尚需进一步监测和分析。南方地区4～6月期间流感爆发的毒株类型变化值得关注。

Objective To understand the epidemiologic charcters of influenza in China from 2001 to 2003. Methode Deta of outpatient visits for influenza-like illness(ILI) each week and outbreaks of influenza were collected through National Influenza Surveillance Network, which includes 11 northern and 12 anthern provinces of China. Samples wee colected in the outpatients of ILI from 2001 to 2003 and influenza viruses were isolated and identifial. Results Epidemiologica and labatory surveillance data showed that the annual seasonality of influenza epidemic was clear. The peak Of epidemic of influenza in northern areas was in winter season, during December to January. However, ther were three peaks distributed to Spring (Apr.-May.), Summer (Jun.-Aug.) and Winter (Dec.-Jan) seasons in the southern areas. In the peak months, the number of ILI visits per day and per surveillance hospital had increased two-fold in northern and by 37% in southern China. The baseline of percentages for ILI visits, which calculated with 75th percentiles (P_(75) ), was 13. 68% in the north and 13. 08% in southern China. The age distributbo of ILI was related to seasonal types of influenza. When the predominated strain of the season was influenza B virus, the ratio of the ILI visits younger than 15 year-old, increased obviously. when the predominated stains became influenza A virus, the ratio of patient visits for ILI aged over 25 year-old increased. Of 63 outbreaks of influenza, 92% of them occurred at primary and miaddle schools and usually occured in May (32%). The type of strains usually changed around June. Conclusion The quality of national influenza survillance system is reliable since it was matched between percentages of ILI visits and rates of influenza virus isolation. The different epidemiologic charcteristics in north and south of China was noticed. Peak in spring was shown in southern area and which called for more analysis. The change of the types of strains in the outbreaks during April to June in the southern China could provide data for better understanding on the trend of epidemics in the next season.