Swine-Origin Influenza A (H1N1) and Seasonal Influenza in Qazvin Province, Iran: Comparison of Epidemiological Features, Clinical Manifestations and Outcome of the 2009 Pandemic

Background: Emergence of a novel swine-origin influenza A (H1N1) pandemic since 2009 attracted the attention of scientists to characterize epidemiological features and clinical manifestations of this disease in comparison to seasonal flu in different parts of the world. Objectives: The goal of this investigation was to compare these features in confirmed cases of swine-origin influenza A (H1N1) and seasonal flu in the 2009 epidemic in Qazvin province, Iran. Patients and Methods: This cross sectional study was performed during 2009 in the Qazvin province. The epidemiological characteristics and clinical manifestations of all cases with severe flu-like manifestations were registered. Diagnosis of confirmed cases of both groups was performed by Real Time-Polymerase Chain Reaction (RT-PCR) on respiratory secretions of positive cases of swine-origin influenza A (H1N1) and seasonal influenza that were entered in the study. Analysis of quantitative data was performed using paired t-test and those of qualitative variables by chi square and Fisher’s exact test. Results: Among a total of 518 patients with clinical signs of severe influenza throughout the Qazvin province, 76 confirmed cases of swine-origin influenza A (H1N1) and 36 cases of other types of influenza A (seasonal influenza) were detected. The mean age of the first group was 25.67 ± 16.9 years and that of the second group was 36.03 ± 19.8, with a significant difference between the two groups (P < 0.01). The appearance of diarrhea was significantly higher in patients with swine-origin influenza compared to those with seasonal influenza (P < 0.005). There was no statistically significant difference in the number of hospitalizations, need for intensive care, assisted ventilation, and mortality rate between the two groups. Conclusions: Higher prevalence of disease in younger individuals, higher rate of gastrointestinal manifestations and occurrence outside of the epidemic season, were the most important characteristics of swine-origin influenza in comparison to seasonal influenza, in the 2009 pandemic of Qazvin province, Iran. Keywords: Influenza A Virus, H1N1 Subtype; Epidemiology