1.1.2 Clinical evidence linking allergy to risk of viral upper respiratory infection.
From a clinical point of view, the results are more controversial than those from the laboratory. Studies in the literature comparing the incidence of upper respiratory infections between allergic and non-allergic subjects are relatively few in number (see 4 articles included in the qualitative analyses in table II).
In two manuscript has been demonstrated that atopic/allergic patients had increased susceptibility to upper respiratory infections. In 2006, in a large cross-sectional survey Karevold et al.(21)demonstrated that atopy increases the risk of developing upper and lower respiratory tract infections in children. In particular, atopy was the strongest risk factor, such as in the home environment (dampness). Accordingly, Ciprandi et al.(22) observed that allergic children have a significantly higher number of upper respiratory infections, more serious in duration and severity, compared with non-allergic ones.
Other authors disagree: Kværner et al.(23) reported that correlation between upper respiratory infection and atopic diseases from a population-based sample of 7992 Norwegian twins was weak, even though results were inconclusive. Sütçü et al.(24)confirmed that the number of episodes per year was not significantly different between atopic and healthy children, even though atopic ones had longer episodes of recurrent URTI compared to controls.
Interestingly all clinical studies included in the qualitative analyses about therapy (Table II) supported the hypothesis that anti-allergy specific or non-specific treatments may prevent viral infections of the upper airways. Antihistamine therapy can act by reducing the expression of adhesion viral receptors to modulate the production of TH-2 related interleukins(22). Authors(16,25)demonstrated that children treated with cetirizine had a significant reduction in ICAM-I expression on epithelial cells, thus preventing possible relapse of rhinovirus infections and diminishing both the number and severity of recurrent respiratory infections in children. Barberi et al.(26, 27) demonstrated that children treated with sublingual immunotherapy (SLIT) had significantly fewer respiratory infections (RI) than symptomatically treated children. In addition, SLIT-treated children had less fever episodes per year and took fewer medications vs. symptomatically treated children.