Epidemiology of Influenza in Fars Province, Southern Iran; a Population-Based Study (2015-2019)

Background: Influenza is one of the most important viral diseases with high mortality and morbidity that can have a great impact on public health and economy. Objective: To investigate the clinical and epidemiological features of influenza virus A/H1N1, A/H3N2, and B infection in Fars province, southern Iran, in 2015-2019. Methods: In this retrospective cross-sectional study, we assessed the archived data of Syndromic Surveillance System of Iran's Health Ministry, allowed access by Communicable Diseases' Unit of Health chancellor of Shiraz University of Medical Sciences, from December 22, 2015 to September 22, 2019. The participants included all patients whose data were recorded as influenza-like illness (ILI) and severe acute respiratory infections/illness (SARI). Influenza viral infection was confirmed by reverse-transcriptase polymerase chain reaction (RT-PCR). Results: Totally, 1269 patients suspected of influenza were sampled. The mean +/- SD of age was 29.40 +/- 26.91 years. Fever was the most common symptom (68.6%). The highest incidence was in winter (55.9%). Of 928/1269 laboratory's results which were recorded in the registry, 204 (16.08%) samples were positive and 724 (57.05%) were negative. Among 204 positive results, 191 (15.05%) were influenza type A, and 8 (0.63%) influenza type B. Among patients with definite influenza type A, 34 (2.68%) had H1N1/p subtype, 58 (4.57%) H3N2, and one (0.08%) had other subtypes; however, subtypes were not identified in 7.72% of patients. Six (3.0%) patients with confirmed influenza expired. Conclusion: The incidence of influenza, especially type A, in Fars province, southern Iran is considerable and requires more attention for prevention in health policy programs.