Comparison of virological profiles of respiratory syncytial virus and rhinovirus in acute lower tract respiratory infections in very young Chilean infants, according to their clinical outcome

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.

Keywords: ALTRI; Respiratory syncytial virus; Rhinovirus; Severe infantile respiratory infection.

Fig. 1

Comparison of rhinovirus clinical isolates phylogeny using Neighbor-joining method. A total of 117 reference sequences obtained from Genbank were used for alignment and 43 of them are shown in the figure. Genbank accession numbers are indicated. Isolates were assigned to genogroup to which they clustered in the phylogenetic tree with a significant bootstrap value >50% . HRV genogroups are indicated in the right side of each branch. HRV-Ca belongs to genogroup C but genetic similarity in the 5′NCR region forces clustering with HRV-A , , , , .