Based on our phylogenetic analysis, the respective frequency distribution of strains infecting the URT and LRT did not reveal any apparent correlation between a given HRV serotype or species and their ability to infect the LRT. In both lung transplant recipients and hospital patients, HRV-A and -C strains presented a similar propensity to infect the LRT. No HRV-B strains were found to be associated with LRT, but the relatively small number of infected samples precludes us from drawing firm conclusions. In this respect, we have previously described chronic LRT HRV-B infections [8] . In our study, protracted infections were all found in hosts with a very low level of immunity (mostly lung transplant recipients and a 3-month-old infant). These results suggest that host factors are determinants of disease outcome, rather than virus type.