Surveillance of influenza viruses in Guangdong Province, China in 1998: a preliminary report

Background: Since cases of humans infected with avian influenza A(H5N1) virus were reported in Hong Kong, the world has been surprised. Guangdong Province has a similar climate and geographic environment to Hong Kong, and a prosperous poultry market gives rise to the potentiality of an epidemic or outbreak of human infection with A(H5N1) virus. Therefore, a strengthened surveillance of influenza viruses was carried out in eight cities of Guangdong Province during March-October 1998. Methods: Samples of throat swabs were taken from outpatients with influenza-like illness and inpatients with bronchitis, pneumonia or other infections in the lungs, and of pharynx fluid from chickens in fanning markets, and then inoculated into embryonated chicken eggs for isolation of influenza viruses. The hemagglutination (HA)-positive fluid derived from the embryonated eggs was then identified by the hemagglutination inhibition (HAI) test. Sera of the occupational group of raising, selling and slaughtering chickens and the general group were taken and tested for antibody to influenza viruses by HAI. Results A total of 8563 specimens of human throat swabs were collected and 242 isolates were identified as flu viruses. Of 242 isolates, 193 were A(H3N2), 4 were A(H1N1), 36 were type B and 9 were A(H9N2). A(H5N1) virus was not found. The predominant strain was A(H3N2), making up 79.8% of the all isolates, followed by type B (14.8%), Of 9 A(H9N2) viruses, 4 were isolated in Shaoguan City and 5 in Shantou City, respectively. The time distribution of influenza viruses isolated was 10 isolates in March, 52 in April, 45 in May, 52 in June, 34 in July, 28 in August, 17 in September and 4 in October. Of 9. A(H9N2) viruses, 2 strains were isolated in July, 6 in August and 1 in September, respectively. HAI titers of H9 antibody were 1:160 in one of nine suspected cases from whom A(H9N2) were isolated. Antibodies to A(H5N1) were not detectable in 1512 sera of occupational group and 885 sera of general individuals. Conclusions: In the surveillance of influenza, 242 influenza viruses were isolated from 8563 specimens of human throat swabs viruses in Guangdong Province, China 1998. The predominant strain was A(H3N2). Nine strains of A(H9N2) were isolated from human throat swabs. (C) 2001 Elsevier Science B.V. All rights reserved.