AETIOLOGICAL STRUCTURE OF ACUTE RESPIRATORY TRACT INFECTIONS AMONG CHILDREN YOUNGER THAN 5 YEARS IN BULGARIA

Acute respiratory tract infections (ARI) are a leading cause of morbidity and hospital admissions among infants and young children. This study aims to determine the viral aetiology of ARI and the clinical significance of the most common respiratory viruses in children aged <5 years in Bulgaria. During the period October 2017-March 2019, nasopharyngeal specimens were collected from children younger than 5 years in different country regions. Real-time PCR analysis was performed for detection of influenza viruses A/B, respiratory-syncytial virus (RSV), human metapneumovirus (HMPV), parainfluenza viruses (PIV) types 1, 2 and 3, rhinoviruses (RV), adenoviruses (AdV) and bocaviruses (BoV). Of the 953 children examined, 663 (69.6%) were positive for at least one virus. The number of detected A(H1N1)pdm09, A(H3N2), B/Yamagata, B/Victoria, RSV, HMPV, PIV-1, PIV-2, PIV-3, RV, AdV and HBoV viruses was as follows: 150 (15.7%), 51 (5.6%), 50 (5.2%), 1 (0.1%), 193 (20.3%), 38 (4%), 15 (1.6%), 5 (0.5%), 17 (1.8%), 101 (10.6%), 60 (6.3%), 77 (8.1%), respectively. Co-infections with two and three viruses were found in 95 (14.3%) of the infected children. AdV, RV, BoV and PIV-3 were the most common pathogens in co-infections. Respiratory viruses were detected in 80%, 79.3%, 61.2% and 53.1% of children with laryngotracheitis, bronchiolitis, pneumonia and central nervous system (CNS) complications. The results show that RSV, influenza viruses, RV and BoV were the most frequently detected viruses in children <5 years with ARI during the study period. These viruses were also leading causative agents of serious illnesses of the respiratory tract and CNS.