“…In addition, a recent study performed in mice (Lukacs et al, 2006) shows the different disease characteristics caused by two different strains of RSV-A, A2 and Line 19, independently of virus replication, thus suggesting different RSV pathogenicities within the same antigenic group; (4) patients with bronchiolitis were significantly younger than patients with other lower RTIs. This seems to be largely due to the younger more immature host immune system (Bont and Kimpen, 2002;Marchant and Goldman, 2005;Roman et al, 1997;van Drunen Littel-van den Hurk et al, 2007), which causes an inappropriate shift toward a Th2 immune response to RSV infection, thus resulting in bronchiolitis; (5) symptom duration was significantly longer in patients with bronchiolitis; (6) 7/10 patients examined after discharge still shed virus 20-30 days after onset of symptoms. It remains to be defined if virus persistence in NPA is due to virus' characteristics or to an impaired RSV clearance resulting from an inefficient immune (in particular IgE) response; (7) male sex is independently associated with a higher risk of RSV bronchiolitis (p = 0.018).…”