In this study, respiratory pathogens were assessed in asthmatic children with 2-16 years of age in the pilgrimage and tourist region of the Khorasan Razavi Province in the northeast of Iran. The results were consistent with those observed by several authors around the world, accompanied by various respiratory pathogens (21, 22). The key findings of this study were a) H1B following by HRSV-A,B, PV, EV, HCoV-43, HCoV-HKU and flu-B are the most frequent pathogens in children associated with asthma symptoms, b) male children were more susceptible to the respiratory infections than the female children, and c) compared to the adults, the infants and children were more vulnerable to the respiratory viruses (7, 23-25). The results in the current study showed that exposure to viruses in children with asthma could increase the airway obstruction, inflammation and lung dysfunctions, causing asthma exacerbation. The data clarify the vital function of viral respiratory infections in the asthma exacerbations and confirm the close connection of viral infection and asthma deterioration. Viral infections are generally recognized as important contributors to acute asthma exacerbations (50–85%) (26-28). However, prospective monitoring of nasopharyngeal samples during the peak season for viral infections and asthma exacerbations provides evidence of a close relationship between viral, bacterial, and respiratory symptoms. Although it has been shown that allergen exposure, gender, age, environmental and inherited factors are associated with asthma exacerbations; previous studies proposed the high rate of viral respiratory infections and their inflammatory responses as the major cause of morbidity and mortality in asthmatic patients (29-31). Our data is consistent with prospective studies demonstrating that the asthma exacerbations coincide with the prevalence of respiratory viruses, particularly in autumn and winter (32, 33). In individuals who were monitored regularly, respiratory viruses are discovered in ~ 40% of asthma worsening (10, 34, 35). According to the results of the analysis, some specific infections such as H1N1, EV and AV have a close connection with asthma attack, bronchitis, food allergy, atopic dermatitis and rhinitis, respectively (36). Also, our findings showed that it is more likely that after colonization of the viral respiratory infections, S.pneu infection worsened the asthma attacks because of the weakness of the immune system.
A positive correlation between RSV-A, B with allergy and rhinitis symptoms was also notified. Former clinical surveys approved the role of RSV, and to some extent, that of HMPV in induction of asthma in the respiratory tract. Our collected data is in line with other surveys showing that RSV and picornaviruses infections were mostly associated with acute expiratory wheezing in hospitalized infants (17, 37-39). Asthmatic infant girls who are immunocompromised are more at risk of severe viral infections of viruses such as coronaviruses (40, 41). Regarding influenza viruses, the studies have shown that influenza is safe for asthmatic patients (42). The low rate of flu-B and negative case of flu-A in the current study are consistent with the results that showed flu viruses caused respiratory diseases in young and middle-aged individuals more than children (43). Some studies have shown that the spread of flu with S.pneu causes pneumonia, bronchitis, sinus infections and ear infections (44, 45). However, in the present study, although S.pneu was frequent in asthmatic children and was associated with the exacerbation of the asthma attacks, there were no flu infections in our study population.
Similar to previous studies, a low rate of HPIV in asthmatic children was observed. However, the incidence of H1N1 infection was significantly higher in asthmatic children than non-asthmatic children (46, 47). This result is inconsistent with our results which also cover autumn. The present study also showed that children seem to have lower rate of respiratory viral infection than adults, but the asthma attacks could occur in the presence of infection colonization. In addition, viral infections associated with the opportunistic bacterial flora are more likely to be symptomatic, and in children with asthma, they are more likely to be associated with asthma exacerbations. A recent pooled meta-analysis of 60 studies across all ages and continents found the prevalence of respiratory viruses associated with asthma exacerbations was <15% (16). However, the present study showed that around 39% of microbial asthma is viral. Notably, the low rates of positive viruses in asthmatic older children in our study could be explained by the fact that exposure to some bacterial or viral products has increased the maturity of innate and acquired immunity.
Our study indicated a predominant circulation of H1B bacteria in asthmatic individuals. This opportunistic bacterium was detected in 41.5% of the studied children with asthmatic exacerbations, which in consistent with some other studies on adulthood(48). Although H1B, S.aur, S.pneu and C.pneu are more detected in infant and school-aged children, other infection agents are less common in adolescence (45).
Mixed etiology and different pathogenic roles of viruses and bacteria lead to existence in respiratory secretions in combination or alone. The findings of our study are shown in Fig. 1 and 2, and, surprisingly, mixed bacterial infections of S.aur, S.pneu and C.pneu have been more common in 15% of the infections, and in a single infection the S.aur was predominant. It seems that S.aur alone or in the mixed bacterial infection has been the main cause of triggering asthma attacks in this region.
S.aur develops the chronic rhinosinusitis via a TH2-biased immune response to staphylococcal enterotoxins (SE) through both IgE-independent and IgE-dependent inflammatory reactions (49). Nasal colonization with S.aur is known to worsen eczema (49, 50). Aside from eczema, S.aur has been implicated in the development and severity of allergic rhinitis, asthma, and food allergy. Building on these findings, S.aur nasal colonization could be nominated as a risk factor for a range of asthma-associated outcomes, including diagnosis, symptoms, and exacerbations, among the population.
Furthermore, although HIB has been more frequent bacterial infection in asthmatic children, it could only exacerbate the asthma attacks around 5% and 41% as mixed with other bacterial or viral infections, respectively. The close association of bacteria and, to lesser extent, opportunistic respiratory viruses is little known in asthmatic children. Although evaluating the overall contribution of each virus/bacteria to disease severity is complicated by the presence of many confounding factors in clinical studies, understanding the role of each virus/bacteria in defining the asthma outcome will potentially reveal novel treatment and prevention strategies and also improving patient outcomes (51, 52).