The Study And Its Application Of Influenza Surveillance In Guangdong Province

Objective To explore the law of influenza activity for the control and prevention of influenza. Methods By active surveillance system(influenza surveillance system), and passive surveillance system (the reporting system of legally determined infectious diseases), surveilling influenza epidemiologically, etiologically, serologically and molecular epidemiologically. Results Epidemiological surveillance in 2001 Active surveillance system found that 35.24%~42.18% of the total outpatients in 2001 were respiratory infection cases in 9 monitor hospitals of 7 area-class cities in Guangdong province, the percentage from January to July showed an increasing trend and reached the peak in July (42.18%), while it showed a decreasing trend in the latter half year. There were only two outbreaks of B-type influenza reported during the whole year. Pathogenic surveillance in 2001 There were 258 strains of influenza viruses isolated, 101 identified as A(H1N1), 47 as A(H3N2) and 110 as B type. The predominance strain was B type during January to June, 2001, yet was A(H1N1) during July to August, and change to A(H3N2) after September. The positive rate of the isolated viruses had a great reduction after August. Serological surveillance in 2001 The positive rates of antibodies against H1N1, H3N2, B(Victoria) and B(Yamagata) in general group were 64.44%, 70.22%, 57.76% and 20.84% respectively. The positive rates of antibodies against H5 and H9 in avian related group were about 0% and 28.67% respectively. Molecular epidemiological surveillance in 2001 The surveillance found that there was still "D" phase influenza A(H3N2) virus prevalent in Guangdong. This subtype, with only 91.5-93.6% of HA1 homology and 5 amino acids'variation in the receptor-binding site (RBS), was much different from "O" phase virus currently prevalent in their antigenicity. The passive surveillance system found that in recent 5 years influenza activity was gradually becoming weak, and its activity peak was mainly in April to July, which corresponded to the law of influenza activity in Guangdong province. It is quite different in the north of China. Conclusion Influenza surveillance predicted accurately that there was no epidemic in 2001 in Guangdong province. After H3N2 influenza virus appeared "O" phase variation globally in 1996, there was still the activity of D phase influenza A(H3N2) virus, which suggested that a close attention must be paid in our future surveillance work and proper isolation methods and identification sera had to be chosen. Passive surveillance system, because of too high missing report rate, is not suitable to be used to estimate the incidence and only can be use for the estimation of epidemic trend. For surveillance sensitivity, the speed of data transmission in the influenza surveillance network needs to be further promoted in Guangdong province. According to the law of influenza activity, there would be consequentially a new epidemic peak coming after keeping silent for some time. We must strengthen further the later prevention and control work although the influenza activity appeared silent in recent years. Influenza surveillance in Guangdong is very important, because of the special geographical situation of this province, Southern China postulated as the epicenter of influenza epidemics, and the outbreak caused by an influenza virus (H5N1, H9N2) in year 1997 to 1999. Whether or not there is any possibility that the avian flu virus becomes a pandemic strain in human has became a matter of global concern.