Epidemic changes of influenza A virus and analysis of differences in laboratory detection methods in Nanyang, Henan from September 2019 to April 2023

Objective To understand the epidemiological characteristics and method specific detection of Influenza A viruses in Nanyang, Henan province.

Methods Peripheral venous blood, pharyngeal swabs and alveolar lavage fluid samples of fever patients with suspected influenza A virus infection were collected from Nanyang Central Hospital, Nanyang First People's Hospital, Nanyang Kangsheng Medical Laboratory Corporation and Zhengzhou Jinyu Clinical Testing Center Corporation from September 2019 to April 2023. Indirect immunofluorescence (IFA), magnetic particle chemiluminescence (CLIA), colloidal gold method, first generation sequencing, reverse transcription-polymerase chain reaction (RT-PCR) and Target next generation sequencin (tNGS) were used for the sample detection. The advantages, disadvantages, and correlations of different detection methods were analyzed, and then the spread of influenza A virus was analyzed.

Results A large number of the samples were sent from fever clinics, the influenza A virus infection cases were distributed in all age groups, indicating that all populations were susceptible to influenza A virus, The spread level of influenza A virus was low during 2020–2022, but was high in 2019 and 2023. There were no significant differences in the positive rate of RNA of influenza A virus detected by tNGS, first-generation sequencing, and RT-PCR (χ²=1.449, 0.838, P=0.229, 0.360), including IAV-IgM detection (EUROIMMUN). tNGS and the first-generation sequencing can be used to classify influenza A virus, but the differences in detecting influenza A virus and influenza A (H3N2) virus were significant (u=4.335, 4.213, P<0.001). When the Ct value of RNA of influenza A virus was less than 25, the detection rate of gIAV-A in the patient's throat swabs was relatively stable, with a sensitivity of 97.78%, when the Ct value was ≥30, the detection rate of IAV-Ag remained above 40.00%, and the total sensitivity of the gold standard method for detecting IAV-Ag could reach 77.22%. The first generation sequencing and tNGS showed advantage in detecting RNA of influenza A virus, but IFA and CLIA showed advantage in detecting IgM of Mycoplasma pneumoniae

Conclusion Influenza A virus spread all the year round in Nanyang, but mainly in winter. The detection rate of influenza A virus varied with different methods in different laboratories. The co-detection of RNA and IgM of influenza A virus could provide accurate influenza A virus detection results in clinical practices.