ABSTRACT
Objective To understand the infection status of pandemic 2009 H1N1 influenza after the first epidemic wave and to estimate the infected population. Methods Multi-stage stratified random sampling was introduced with 4500 subjects chosen in Guangdong province. 1500 people were selected from 5 districts (3 streets were selected in every district) in Guangzhou city which was representing the large cities. 1500 people were respectively selected from medium-sized city and rural areas, including 20 cities (1 county or district was selected in every city, at least 1 street or town was selected in every county or district respectively and then 1-2 residential area or county was selected in every street or township, respectively). Every sample was selected in accordance with the principle of random sampling, excluding those who had injected with novel H1N1 vaccine. We used hemagglutination inhibition test to understand the serum antibody level of novel H1N1, with title of 1∶40 as positive. Results A number of 4319 specimens, distributed in 21 cities, 25 counties, 85 streets or townships, 144 residential areas, were tested, with an overall positive rate as 22.82% (985/4319). The positive rate of those who had no symptoms of cold since June was 23.47% (471/2007).The positive rate of those who had fever, cough or sore throat was 26.25% (714/2720). The positive rate of those who had influenza-like illness (ILI) was 29.69% (337/1135 ). Conclusion The infection rate in the first epidemic wave of the novel influenza A (H1N1) pandemic in Guangdong province was 22.82%(985/4317). Based on the number of residonts in Guangdong province, the number of natural was estimated to have reached 21.78 million.