Influenza surveillance in Pune, India, 1978-90

Abstract

Continuous surveillance of influenza was carried out in Pune between 1978 and 1990. Most of the cases were identified during investigation of 16 outbreaks of influenza in Pune over this period. The majority of cases were children. Ten of the outbreaks occurred during rainy seasons. A total of 290 isolates consisting of several antigenic variants of influenza type A (H3N2), type A (H1N1), and type B viruses were isolated from throat/nasal swabs that were processed in chick embryos and MDCK cell culture and identified using the haemagglutination inhibition test. These variants circulated every year or in alternate years. Nearly two-thirds of the influenza virus isolates (181 out of 290) were from children aged < 10 years. Seasonal analysis indicated that the highest number of isolates (174) were collected during the rainy months of July, August and September, with the maximum number (93) in July.

PIP: Under an influenza surveillance initiated in Pune, India, 2 or 3 dispensaries and small hospitals where patients with acute respiratory disease (ARD) sought medical assistance were chosen for regular weekly visits to collect a sufficient number of specimens. A case of ARD included individuals with the following conditions: common cold, pharyngitis, laryngitis, tracheitis, bronchitis, bronchiolitis, pneumonia, or bronchopneumonia. During the period of surveillance of 1978-90, more than 10,000 cases of ARD among various age groups were investigated. The majority of cases were in children and infants. Most of the patients were seen during investigations of 16 outbreaks of influenza. Generally, the cases presented with 2 or 3 symptoms of respiratory disease and 1 or 2 systemic manifestations. Throat and nasal swabs were collected from ARD cases during the acute phase of their illness (1-4 days). Throat/nasal swabs were taken from over 10,000 ARD cases. About 80% of these specimens were cultivated for influenza virus in embryonated chicken eggs (9-11 days' old) and about 39% in Madin-Darby canine kidney cell culture (MDCK) with crystalline trypsin. Several variants of influenza virus types A and B were isolated during the 16 outbreaks including these variant strains: A/USSR/77 (H1N1) in 1978; A/Singapore/6/86 (H1N1) in 1986; and B/Yamagata/16/88-like in 1990. A total of 290 influenza virus isolates comprising several variants of influenza type A (H3N2) and A (H1N1) and type B were isolated. The variant strains of influenza type A (H1N1), type A (H3N2), and type B circulated regularly either every year or in alternate years. 181 of 290 of the influenza isolates were from children aged 10 years. Analysis of the isolates showed that 174 were from the rainy months of July, August, and September, and the maximum number of 93 occurred in July. Of the 16 outbreaks of influenza, 10 occurred in the rainy season, 3 in the hot season, 1 in the cool season, and 2 in February and March.