Objective: to estimate the prevalence and clinical-epidemiological features of acute respiratory infections of various etiology in children of the first three years of life, hospitalized to the intensive care unit of a children’sinfectious hospital.

150 children of the first three years of life of the total number of patients, hospitalized to the intensive care unit of the Republican Clinical Infectious Diseases Hospital of Kazan with a severe ARI, were randomly selected. The design of the research was consistent with the observational analytic.

Results: the etiology of  ARI was interpreted in  74% (95% CI 67–81), 111/150 cases. Rhinovirus infection is the main cause of development of severe forms of ARI in young children; in second place – influenza viruses – 13.9-28.7% in different age groups. Clinically significant in all age groups were respiratory syncitial viruses (7.1–16.7%), in children up to one year – parainfluenza viruses (13.9% (95% CI 6–21.8), 10/72, and in  patients older than 2 years  – adenoviruses (12–14.2%). Seasonal rise in  the incidence of ARI was noted in the cold season. It was caused by influenza viruses, respiratory syncitial viruses, parainfluenza viruses. In the summer months, the rhino-, metapneumo- and adenoviruses were most common. The expressed general toxic effects that caused hospitalization were recorded in 66% (95% CI 58.4–73.6), 99/150 of the examined patients, manifestations of respiratory failure was detected in 58% (95% CI 50.1–65.9), 87/150.

Conclusions: the leading causes of development of  severe forms of ARI in young children are rhinoviruses, influenza viruses and the respiratory syncitial virus. They are associated with: respiratory tract diseases with respiratory failure, a symptom complex of  toxicosis. Previously thought «harmless», rhinovirus infection is becoming a leader in  the range of  causes of  severe forms of respiratory infections in young children.