Influenza surveillance and excess associated mortality in Guangzhou, China

Abstract

Background/Aims: Although surveillance for influenza-like illness (ILI) is widely accepted as syndromic surveillance of influenza, the question remains whether ILI surveillance can serve as an early warning of influenza activity. There is a great deal of evidence that influenza is associated with considerable morbidity and mortality. However, few studies of disease burden of influenza are from outside developed countries. This study aimed to describe surveillance of influenza and assess mortality impact of influenza in Guangzhou, China.

Methods: Guangdong Center of Disease Control and Prevention (CDC) provided data of weekly number of ILI and influenza virology data for the 3-year period of 2004–2006 in Guangzhou, China. The influenza data was matched with weekly counts of mortality and meteorological measures. Cross-correlation was performed to examine the time lag between weekly number of cases with ILI and positive rate of influenza isolation, after filtering the trend and seasonality of each time-series and controlling for meteorological effects. Poisson regression was used to model weekly counts of mortality on influenza activity after adjustment for potential confounding.

Results: Influenza was circulated through the whole year during the period 2004–2006 in Influenza was circulated through the whole year during the period 2004–2006 in Guangzhou, China. Variation of weekly number of ILI cases preceded the positive rate of influenza isolates by 3 weeks. The excess mortality associated with influenza was 2.8% and 6.6% for cardiovascular diseases and respiratory diseases, respectively. Correspondingly, the influence-associated deaths per 1000 population were 6.4 and 7.3, respectively. The estimates of ILI-associated mortality were triple or fourfold.

Conclusion: Compared with laboratory-based virology surveillance, clinical surveillance of ILI from sentinel hospitals offers earlier warning of increased incidence of influenza in population. Influenza poses a substantial burden on mortality in Guangzhou, China, where the virology surveillance of influenza should be strengthened.