Abstract

Background Respiratory syncytial virus (RSV) and rhinovirus (HRV) are the main cause of acute lower respiratory tract infections (ALRTIs) in infants. Viral and host-related risk factors for severe disease have also not been clearly established. Objective To assess whether certain viral features of RSV and, or HRV are associated with severe ALRTI. Study design RSV and HRV were studied in nasopharyngeal samples of infants by immunofluorescence, Luminex® and/or real-time RT-PCR assays. Quantitation and genotyping of RSV and HRV by PCR were done. Results Of 124 virus positive specimens, 74 (59.7%) had RSV; 22 (17.7%) HRV and 28 (22.6%) RSV-HRV co-infection. Hospitalization was required in 57/74 RSV infants (77.0%); in 10/22 HRV cases (45.5%) (p = 0.006) and in 15/28 co-infected by both viruses (53.6%) (p = 0.003). Severe cases were 33/74 (44.6%) RSV infections, 2/22 HRV cases (9.1%), (p < 0.002) and 6/28 (21.4%) patients co-infected by RSV–HRV (p < 0.026). Three genotypes (NA1, B7, B9) of RSV circulated during the study. In 33 severe infants, NA1 was detected in 19 cases (57.6%); B7 in 13 (39.4%) and B9 in 1 (3.0%) (p < 0.01; OR = 10.0). RSV loads were similar between outpatients and hospitalized infants (p = 0.7) and among different severities (p = 0.7). NA1 loads were higher than other strains (p = 0.049). Three geno-groups of HRV circulated homogeneously. Conclusion In very young infants, RSV cause more severe disease than HRV. Co-infection does not increase the severity of illness. NA1 RSV genotype was associated with major frequency of hospitalization, severe respiratory disease and higher viral load.