Viral spectrum of 36 outbreaks of influenza like-illness in Shandong province

Objective To understand the viral spectrum of influenza-like illness (ILI), Shandong province during 2013-2014. Methods The data of 36 ILI outbreaks were collected and analyzed. Multiple respiratory pathogens were detected with RT-PCR in pharynx swab specimens. Results Totally, 35 outbreaks occurred in winter and spring, and dispersed in 12 cities; 27 outbreaks happened in primary and secondary schools. Many of the outbreaks, 17 (47.2%), were caused by influenza virus type B (FluB), followed by FluA H1 and H3, 5 (13.8%) outbreaks, respectively. Mixed infection caused 7 outbreaks. Totally 437 samples were collected, with 235 (53.8%) positive specimens, in which FluB was mostly detected, 142 (32.5%). Except Flu, parainfluenza virus type 2 (PIV2) was the most frequently detected, followed by coronavirus (CoV). The constituent ratio of FluB under 15 years of age was the highest, such as CoV in 25-59 years old group and FluA H1 in others groups. Conclusions ILI outbreaks occurred mostly in primary and secondary schools. Virus was the main pathogen, with the dominant strains of FluB. However, the dominant strain in different age groups was different. Key words: Influenza-like illness; Influenza virus; Outbreak; Parainfluenza virus; Coronavirus