Demographic, clinical, and virological characteristics of patients with a laboratory-confirmed diagnosis of influenza during three consecutive seasons, 2015/2016-2017/18, in the Islamic Republic of Iran.

Background: There are minimal data on the differences in demographics, clinical presentations and outcomes for patients with different types and sub-types of influenza in the Middle East.

Objectives: To use population-based data from Iran to investigate factors associated with unfavorable disease outcome.

Study Design: Clinical data were compiled from the Iranian Ministry of Health for patients of all ages who fulfilled the severe acute respiratory infections (SARI) definition according to World Health Organization criteriatested for any reason and found to have and had laboratory proven influenza September 21, 2015 through March 20, 2018. Pulmonary, cardiac, renal, hematologic and neurologic complications were recorded. Results were compared by type, age, gender and health status. Multivariate analysis was used to analyze risk factors for complications and death.

Results: Of 11,080 enrolled patients, 10,046 (90.7 %) were inpatients, 2254 (20.4 %) were children, 8403 (75.8 %) had influenza A, 2599 (23.5 %) had influenza B, and 78 (0.7 %) had unidentified types. Fever was less common in older patients (OR 0.99; 95 % CI 0.98-0.99, p < 0.001 and in those with comorbidity (OR 0.87; 95 % CI 0.77-0.97, p = 0.013). Although the rate of complications was lower with A(H1N1) pdm09 influenza than with A(H3N2) infection (12.8 % versus 15.6 %, p = 0.001), the mortality rate was higher (7.0 % versus 3.0 %, p < 0.001). Complications occurred more often during late versus early influenza season (OR 1.22; 95 % CI 1.08-1.37, p = 0.002). Patients with type B influenza (OR 0.85; 95 % CI 0.74-0.98, p = 0.025), or who presented with sore throat (OR 0.74; 95 % CI 0.65-0.84, p < 0.001) were less likely to develop complications. The risk of developing complications was increased in patients who had chronic heart disease (OR 1.51; 95 % CI 1.29-1.76, p < 0.001), chronic pulmonary disease (OR 1.62; 95 % CI 1.37-1.91, p < 0.001), diabetes (OR 1.24; 95 % CI 1.03-1.50, p = 022), or epilepsy (OR 1.55; 95 % CI 1.17-2.05). Older age and male gender increased the risk of death but not of complications.

Conclusions: The clinical features, complications and outcomes of influenza vary by age and by viral type and sub-type. Comorbidites appear to be more important than age in predicting complications.