Figure 1.

Three potential models to explain the observed association between RSV-LRTI and subsequent wheezing illness

(A) RSV-LRTI as one of multiple causal contributors to wheezing illness. There is a directed solid arrow (representing a causal effect) connecting RSV-LRTI and wheezing illness. (B) A non-causal model in which the positive association between RSV-LRTI and subsequent wheezing illness is confounded by a pre-existing susceptibility to respiratory illnesses. According to this model, this pre-existing susceptibility is driven by genetics and early environmental insults that precede RSV-LRTI. The dotted, non-directional line connecting RSV-LRTI and wheezing illness represents a non-causal association. (C) The association between RSV-LRTI and subsequent wheezing illness is due partly to the confounding influence of pre-existing respiratory illness susceptibility and partly to a causal effect of RSV-LRTI. RSV-LRTI=respiratory syncytial virus lower respiratory tract infections.