Syndromic surveillance and prediction of influenza in Zhuhai,2006-2008

Objective To analyze and predict the trend of prevalence and predominant strains of influenza viruses and provide scientific basis for the prevention and control of influenza in Zhuhai.Methods Epidemiological surveillance was performed by 28 sentinels. Influenza-like illness(ILI) cases of out-patient were reported weekly. Influenza viruses were isolated from nasopharynx specimens collected by doctors from ILI cases in sentinel hospitals. The information of outbreaks collected through influenza surveillance network and daily surveillance was used to predict the tendency of ILI% in 2009 with autoregressive integrated moving average model (ARIMA).Results Influenza virus prevalence exhibited seasonal bimodal pattern,with one peak in March to April and another in Jun to July. The weekly percentage of out-patient visitors for ILI (ILI%) ranged from 1.5% to 10.1% during 2006 -2008,and the average was 4.1%.Children under five years of age were the main part (50.3%) of ILI. There were 3,216 specimens tested for influenza viruses and 321 (10.0%) were positive. Of the positive specimens,230 (71.7%) were influenza A virus,and 91 (28.3%) were influenza B virus.The influenza A (H1N1) virus and influenza A (H3N2) virus circulated simultaneously in 2006,influenza A(H3N2) virus predominated circulation in 2007,and influenza A(H1N1) viruses and influenza A(H3N2) virus circulated simultaneously in 2008. Outbreaks of influenza occured mostly in March to June.Conclusion Influenza prevalence showed two peaks distributed in spring and early summer in Zhuhai.ILI precedeed the oscillations of laboratory surveillance by about four weeks. The construction of subtype strains usually take turns to be the annually outstanding subtype. The curve predicts that the epidemic tendency of seasonal influenza in 2009 will be stable.