Influenza-associated mortality in temperate and subtropical Chinese cities, 2003–2008

Abstract

Methods Mortality data and population denominatorsAs China has no national system for the registration of vital statistics, we focused on eight cities (Appendix A, available at: http://www.chinacdc.cn/xiazai/Feng-BullWorldHealthOrgan- 2012-AppendixA.pdf)with high-quality, population-based systems for mortality registration and low rates of underreporting and misclassification in the study period (2003-2008).Three of the cities (Dalian, Qingdao and Zhaoyuan) lie in the temperate north of China and have a combined population Objective To estimate influenza-associated mortality in urban China.Methods Influenza-associated excess mortality for the period 2003-2008 was estimated in three cities in temperate northern China and five cities in the subtropical south of the country.The estimates were derived from models based on negative binomial regressions, vital statistics and the results of weekly influenza virus surveillance.Findings Annual influenza-associated excess mortality, for all causes, was 18.0 (range: 10.9-32.7)deaths per 100 000 population in the northern cities and 11.3 (range: 7.3-17.8)deaths per 100 000 in the southern cities.Excess mortality for respiratory and circulatory disease was 12.4 (range: 7.4-22.2) and 8.8 (range: 5.5-13.6)deaths per 100 000 people in the northern and southern cities, respectively.Most (86%) deaths occurred among people aged ≥ 65 years.Influenza-associated excess mortality was higher in B-virus-dominant seasons than in seasons when A(H3N2) or A(H1N1) predominated, and more than half of all influenza-associated mortality was associated with influenza B virus.Conclusion Between 2003 and 2008, seasonal influenza, particularly that caused by the influenza B virus, was associated with substantial mortality in three cities in the temperate north of China and five cities in the subtropical south of the country.