Influenza surveillance in Huzhou during 2011-2017

ObjectiveThe influenza monitoring results in Huzhou city were analyzed to understand the characteristics of influenza pandemic and to provide a scientific basis for prevention and control of influenza.

MethodsThe influenza-like cases(ILI)were collected from two sentinel hospitals in Huzhou according to the protocol of The National Influenza Surveillance Program. Pharynx swab samples of the ILI were taken randomly for the test of influenza virus.

ResultsAmong 5 322 788 patients who went to the sentinel hospitals in Huzhou from 2011 to 2017, 185 010 were ILI. The percentage of ILI was 3.48% and there was a slowly rising trend in ILI% of month from 2011 to 2017(trend χ² = 2 970.93, P < 0.001). Winter /spring and summer seasons marked the peaks in influenza epidemics. Patients were mostly children under 14 years old(accounting for 89.1%). In a total of 11 490 throat swabs collected from ILI, 1 975 were tested to be positive for influenza virus(positive rate 17.19%). These included A type H3N2, 1 008; A type H1N1, 350; B type, 614(160 Victoria type, 238 Yamagata, 216 unclarified B type), and 3 mixed type. The correlation between positive rate of influenza nucleic acid test and ILI% is statistically significant(r = 0.40, P < 0.001).

ConclusionThe incidence peaks of influenza in Huzhou are mainly in the winter /spring and summer periods. The influenza is mainly occurs in young people under 14 years old and the main type virus is A(H3N2). The prevalence of influenza B and H1N1 occurs at intervals. There is a positive correlation between influenza activity and ILI%.