Characterizing the epidemiology, virology, and clinical features of influenza in China's first severe acute respiratory infection sentinel surveillance system, February 2011-October 2013.

BACKGROUND: After the 2009 influenza A(H1N1)pdm09 pandemic, China established its first severe acute respiratory infections (SARI) sentinel surveillance system. METHODS: We analyzed data from SARI cases in 10 hospitals in 10 provinces in China from February 2011 to October 2013. RESULTS: Among 5,644 SARI cases, 330 (6%) were influenza-positive. Among these, 62% were influenza A and 38% were influenza B. Compared with influenza-negative cases, influenza-positive SARI cases had a higher median age (20.0 years vs.11.0, p=0.003) and were more likely to have at least one underlying chronic medical condition (age adjusted percent: 28% vs. 25%, p<0.001). The types/subtypes of dominant strains identified by SARI surveillance was almost always among dominant strains identified by the influenza like illness (ILI) surveillance system and influenza activity in both systems peaked at the same time. CONCLUSIONS: Data from China's first SARI sentinel surveillance system suggest that types/subtypes of circulating influenza strains and epidemic trends among SARI cases were similar to those among ILI cases.

[Clinical characteristics of hospitalized cases of severe acute respiratory infection with laboratory-confirmed influenza and the risk factors analysis of influenza infection for children under 15 years old in ten provinces in China during 2009-2014].

OBJECTIVE: To identify clinical characteristics of hospitalized laboratory-confirmed influenza cases of children under 15 years old, and their risk factors of influenza infection. METHODS: Analyzing the reports of hospitalized laboratory-confirmed influenza cases of children under 15 years old who were detected by the sentinel surveillance systems in 10 provinces from December 2009 to June 2014. Such data as their demographic, medical history, clinical symptoms and signs, treatment and outcome were collected using questionnaires, with their clinical characteristics and their risk factors of influenza infection described. RESULTS: Of the 2 937 severe acute respiratory infection inpatients, 190 (6.5%) were laboratory-confirmed influenza cases. 123 (64.7%) of such confirmed cases were male, and 139 (73.2%) were children under 5 years old, with age median of 3.0 years (IQR: 1.0-5.0 years). 20 (10.5%) of them had at least one chronic medical condition, mostly chronic cardiovascular disease (3.2%), immunosuppressive disease (3.2%), and cancer/tumor (2.6%). Most common clinical symptoms of the cases were fever (92.6%) and cough (88.8%), of which abnormal pulmonary auscultation (51.1%) and abnormal chest X-ray performance (36.1%) were the most common clinical signs. 29 cases (15.8%) had complications, of which pneumonia (15.3%) was most common. 16 cases (8.6%) used antiviral drugs, and 4 cases (2.2%) were admitted into ICU. Risk factor analysis suggested that age < 6 months (OR = 0.406, 95% CI: 0.203-0.815) was a protective factor against influenza infection; and age 5-9 years old (OR = 2.535, 95% CI: 1.059-6.066) was a risk factor for influenza infection. CONCLUSION: Hospitalized laboratory-confirmed influenza cases were found mostly in children under 5 years old. Risk exposure for influenza infection varied among age groups.