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

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. 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. 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. 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. 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.