Key result
Among 24,868 samples from patients with influenza-like illness in Chongqing between 2011 and 2015, 13.3% tested positive for influenza virus, with the highest isolation rate in children aged 5-14 years.
Observational (n=24,868)
Yes
Influenza is a significant cause of influenza-like illness in Chongqing, particularly among school-aged children, with seasonal peaks and varying predominant subtypes each year.
Hypothesis-generating for age-targeted influenza surveillance in Chongqing; prospective studies needed to confirm patterns.
BACKGROUND: Chongqing is the largest municipality and located in Southwestern of China, with over 30 million registered inhabitants. There are few reports regarding the epidemiology of influenza in Chongqing. The objective of the paper is to explore the epidemiology of influenza in Chongqing, in order to provide scientific basis for prevention and control of influenza. METHODOLOGY /PRINCIPAL FINDINGS: From 2011 to 2015, we collected information on influenza-like illness (ILI) patients fulfilling the case definition, and took nasalpharyngeal or throat swabs specimens from ILI cases per week at the 7 sentinel hospitals. Specimens were tested by reverse transcription-polymerase chain reaction(RT-PCR) for influenza. Descriptive epidemiology was applied to analyze the epidemiology and etiology of influenza. A total of 9,696,212 cases were enrolled, of which 111,589 were ILI. Of those 24,868 samples from ILI cases, 13.3% (3,314/24,868) tested positive for influenza virus (65.7% influenza A, 34.1% influenza B, and 0.2% influenza A and B co-infection). Among the influenza A viruses, 71.3% were seasonal influenza A(H3N2) and 28.7% were influenza A(H1N1)pdm09. No cases of seasonal A(H1N1) were detected. The isolation rate was highest in children aged 5-14 years old. Influenza activity consistently peaked during January-March in 2011-2015, and June-July in 2012, 2014 and 2015. CONCLUSIONS: Influenza is an important public health problem among ILI patients in Chongqing, especially among school-aged children. It might be beneficial to prioritize influenza vaccination for school-aged children and implement the school-based intervention to prevent and mitigating influenza outbreaks in Chongqing, particularly during the seasonal peaks.
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Li et al. (2016) conducted an observational in Influenza-like illness (n=24,868). Influenza virus was evaluated on Influenza virus positivity rate. Among 24,868 samples from patients with influenza-like illness in Chongqing between 2011 and 2015, 13.3% tested positive for influenza virus, with the highest isolation rate in children aged 5-14 years.
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