Bronchiolitis needs a revisit: Distinguishing between virus entities and their treatments

Jartti, Tuomas; Smits, Hermelijn H.; Bønnelykke, Klaus; Bircan, Ozlem; Elenius, Varpu; Konradsen, Jon R.; Maggina, Paraskevi; Makrinioti, Heidi; Stokholm, Jakob; Hedlin, Gunilla; Papadopoulos, Nikolaos; Ruszczynski, Marek; Ryczaj, Klaudia; Schaub, Bianca; Schwarze, Jürgen; Skevaki, Chrysanthi; Stenberg-Hammar, Katarina; Feleszko, Wojciech

By definition, bronchiolitis is a virus infection, and PCR diagnostics has reached a 100% virus detection rate in severe bronchiolitis. 8 RSV is the most important causative agent of bronchiolitis during infancy, and it has been detected in 50%-80% of the hospitalized bronchiolitis cases (Figure 1 ). 9,10 RV is the second most common viral agent of bronchiolitis during infancy, but it starts to dominate virus detection after 12 months (Figure 1 ). The next most common viruses in connection to bronchiolitis are human bocavirus and human metapneumovirus followed by parainfluenza virus, adenovirus, coronavirus, and influenza virus ( Figure 1 ). Virus coinfections, mostly with RSV and RV, occur in 10%-40% of the severe cases, but reports on their clinical significancy are inconclusive. 9, 10 Respiratory syncytial virus belonging to the Pneumovirus genus in the Paramyxoviridae family is an enveloped single-stranded RNA virus with two antigenically different A and B subtypes with 11 and 23 genotypes, respectively. 11 Although severe reinfections have been reported in young children, they are generally mild. 12 Main risk factors for RSV bronchiolitis include prematurity, chronic lung disease (low lung function), congenital heart disease, other underlying medical conditions, and young age (1-6 months of age), that is, conditions in which excessive mucus in the airways is problematic, as well as deficient interferon responses. 2 Rhinovirus belonging to the Enterovirus genus in the Picornaviridae family is a nonenveloped single-stranded RNA virus, and it comprises a genetically diverse group of viruses. It has three distinct subgroups, A, B, and C, which consist of 83, 32, and 55 genotypes,