Clinical Characteristics and Outcomes of Influenza A (H3N2/H1N1) Infection in Hospitalized Patients: A Report From Iran 2022-2023 Cold Season Outbreak

Background and Aim: Influenza A subtypes H3N2 and H1N1 are currently circulating among humans and are the main cause of seasonal epidemics in the temperate regions. The specific clinical features of influenza H1N1 and H3N2 infections have not been well evaluated in Iranian patients. Materials and Methods: An observational study was conducted on influenza-confirmed patients in Imam Khomeini Hospital Complex, Tehran, Iran from October 2022 to March 2023. The specimens tested positive for influenza, using RT-PCR, were transported to the National Influenza Center (NIC) Laboratory for the typing identification. Different data, including demographics, comorbidities, length of hospitalization, outcomes, paraclinical features, and recent influenza vaccination, were collected. Results: A number of 165 hospitalized patients with influenza infection were included: 148 (89.70%) patients with H3N2 and 17 (10.30%) with H1N1 infections. Among the patients 55.20% were male. The median age was 49 years. The patients were symptomatic for an average of 8 days. The most common symptoms were dyspnea (60.6%), fever (58.8%), and productive cough (37.6%). The median oxygen saturation was significantly lower in the H3N2 group (91%–81.0, 96.0) than in the H1N1 group (95%–90.0, 97.5) (P=0.029). The ground glass opacity (GGO) was the most common (69.1%) pulmonary radiological pattern. Only one patient had received the influenza vaccine in the recent year.. The mortality rate (19 patients: 11.55%) was associated with the cancer and liver diseases. Conclusion: Influenza A (H3N2 and H1N1) can be considered the outbreak cause in Iran in 2022–2023. The vaccination rate was very low and the mortality rate was high. Influenza vaccination is recommended to prevent death, especially in the patients with cancer.