Association of specific viral infections with childhood asthma exacerbations

Hassanzad, Maryam; Nadji, Seyed Alireza; Darougar, Sepideh; Tashayoie-Nejad, Sabereh; Boloursaz, Mohammad Reza; Mahdaviani, Seyed Alireza; Baghaie, Nooshin; Ghaffaripour, Hosseinali; Velayati, Ali Akbar

The most common viruses detected that cause wheezing illnesses during early life are RSV and HRV, with the former associated with a seasonal pattern and the latter occurring throughout the year [15] . Rhinovirus is common in all age groups; RSV is most important in infants and younger children. Children affected with HRV tend to be older than those affected with RSV [18] . Jartti et al. suggested the transition in dominance between HRV and RSV around 12 months of age [19, 20] . This is in accordance with the results we obtained in this study. Therefore, we could explain the preponderance of HRVinduced asthma exacerbations in this study with the longer duration of exposure and also the low number of children less than 1 year of age enrolled in this study. The same results were also obtained in the COAST study, in which HRV was found in 48% of the samples and RSV in 21% of the specimens [6] . RSV was more commonly associated with more severe attacks in this study that may be demonstrating an interplay between age at initial infection, genetic susceptibility, and virus strain, which altogether determine the outcome of the viral infection and the airway disease, which was first suggested by Saglani [20] . RSV infections, particularly the severe ones, are thought to be associated with Th2 polarization of the lung immune response with further sensitization of the host's allergic responses to other molecules [21] .