Respiratory pathogens are frequently detected in samples from children with no respiratory symptoms. Symptomatic cases occurred more often in younger children and with detections of more than 1 respiratory pathogen.

Although there were no differences in the seasonal occurrences and distributions of polymerase chain reaction-detected respiratory viruses, acute respiratory illnesses were frequently associated with increased lower respiratory tract morbidity in young children with cystic fibrosis.

Cystic fibrosis lung disease typically has a course of exacerbations and remissions, suggesting that external factors like viral infections can influence this course. Clinical data suggest synergism between respiratory syncytial virus (RSV) infections and Pseudomonas aeruginosa in cystic fibrosis (CF) lung disease. We studied the influence of RSV infection on adherence of P. aeruginosa to IB3-1, HEp-2, and A549 epithelial cell monolayers in vitro. RSV infection of epithelial cells as well as simultaneous addition of RSV and P. aeruginosa to noninfected cells both strongly enhanced the pseudomonal adherence to epithelial cells. The increased adherence varied from 1.2-to 8.2-fold in case of previous RSV infection, and from 1.7-to 16.1-fold in case of simultaneous addition. We observed direct binding of RSV to P. aeruginosa, and blocking of RSV with heparin eliminated the effect on increased adherence. This suggests that RSV possibly acts as a coupling agent between P. aeruginosa and epithelial cells.

Viral respiratory infections in CF patients are associated with an increase in morbidity at short and long term. Viral infections have a greater impact on CF patients compared to non-CF controls. They result in increased respiratory symptoms, deterioration of Shwachman and radiological scores, prolonged hospitalizations, a persistent decrease of pulmonary function, increased use of antibiotics and a higher frequency of exacerbations at follow-up. In addition, interaction between viruses and bacteria in CF is suggested. Some studies observe increased new bacterial colonization and raised antipseudomonal antibodies in episodes of viral respiratory infections. Experimental data suggest that increased virus replication, impaired specific anti-bacterial defense and increased adherence of bacteria play a role in the pathogenesis of viral respiratory infections in CF. Further knowledge about the role of viruses and interaction with bacteria in CF lung disease might result in new therapeutic strategies to improve prognosis of CF patients.

We found a high HRV exposition with a considerable diverse population of HRV subtypes in young children. These results have major implications for future research into the pathogenic role of HRV in respiratory diseases. Characterisation of subtypes will be necessary to discriminate between prolonged continuity and re-infections in patients with respiratory diseases.