Childhood Influenza in the Outpatient Setting in Shanghai, China

Abstract

Influenza is a common cause of outpatient visits in childhood. Influenza vaccine has been widely used for children ≥ 6 months of age in developed countries based on accumulating evidence on the substantial socioeconomic burden of influenza in children. However, the data of childhood influenza in China are scarce. We carried out a prospective surveillance of influenza among children visiting outpatient clinic for influenza-like illness between June 2009 and May 2011. Respiratory samples were obtained from the enrolled cases and the demographic and clinical data were collected. Of 2356 enrolled cases, influenza was virologically confirmed in 608 (25.81%) otherwise healthy children. Four hundred sixty-eight (76.97%) were influenza A positive (A/H3N2:236, pandemic A/H1N1:219, seasonal A/H1N1:4, A/H3N2 coinfected with pandemic A/H1N1:3, untyped:6) and 142 (23.35%) were influenza B positive (2 coinfected with pandemic A/H1N1). The outbreaks of A/H3N2, pandemic A/H1N1 and influenza B took place in fall, winter and spring, alternatively. More institutionalized children were affected when the outbreaks overlapped with school opening. Among 603 children with a single influenza virus infection, 289 (47.93%) were <3 years old and 283 (46.93%) had close contact with persons who had fever or respiratory infection, of whom, 192 (67.84%) contacts were family members. The annual outbreak of influenza led to a high rate of outpatient visits among children in Shanghai. Outbreaks occurred in younger and institutionalized children. Household members were the main disseminators to spread influenza among children.