The Seasonal Frequency of Viruses Associated With Upper Respiratory Tract Infections in Children

Upper respiratory tract infections (URTI) in children are the most frequent reasons for visiting a family doctor, commonly resulting in inappropriate prescription of antibiotics. In underdeveloped countries, a viral respiratory tract infection may be followed by serious complications. More than 200 viral species are associated with respiratory tract diseases in humans and this number is increasing. This study was carried out to determine the distribution of common viruses responsible for clinical manifestations of upper respiratory tract infections (URTI) in children throughout the 4 seasons of year. This cross-sectional study was performed from October 2009 to September 2010 on 2- month and 12- year -old children with clinical manifestations of acute upper respiratory tract infections referring to the outpatient clinics of a children’s hospital affiliated to Shahid Beheshti University of Medical Sciences in Tehran, Iran. Nasopharyngeal samples were collected and tested for Influenza virus, Parainfluenza, Adenovirus, Respiratory syncytial virus (RSV), Rhinovirus and Enterovirus, by polymerase chain reaction (PCR). One hundred thirty four out of 330 samples (40.7%) were positive for at least 1 of the tested viruses. Adenovirus was detected with a frequency of 29.9%, followed by Rhinovirus (23.1%), Influenza virus (21.6%), RSV and Parainfluenza viruses (12.7% each) and Enterovirus (9%). Adenovirus was more frequent in spring, summer and winter (35%, 22%, and 36.7%, respectively) and Rhinovirus was common in winter (26.7%), followed by spring and autumn (25% each). Frequency of Influenza virus was 22.5% in spring, 15.6% in summer,21.9% in autumn and 26.7% in winter .The rates of RSV were 9.4% ,15.6% ,12.5% and 13.3%, from spring to winter. Enterovirus was isolated in 7.5% samples in spring, rising to 15.6% in summer, falling to 9.4% and then to 3.3% in cold seasons. Parainfluenza was found 2.5% in spring, 21.9% in summer, 18.8% in the fall and 10% in winter. Adenoviruses are the most commonly detected viruses in childhood URTI. Although frequency of different viruses varies according to the seasons of year, this difference is not significant.