The occurence of asymptomatic respiratory viral infections

Abstract

PCR-diagnostics has markedly increased detection rates of respiratory viruses during an acute illness. At the same time high detection rates question the causality between the detected virus and clinical illness. Our objective was to review the literature on the prevalence of respiratory viral findings in asymptomatic subjects and to discuss their clinical significance. We continued the literature search from our previous review on the asymptomatic respiratory virus infections in children. In total, 46 studies, published between 2008 and 2019 were reviewed. In total, 19175 samples from asymptomatic cases and 19510 from symptomatic cases were obtained for virus diagnostics. The virus detection from asymptomatic subjects is relatively common 22%, but markedly at lower rate than in symptomatic subjects 42%. All virus detections were associated with symptomatic illness except coronavirus, enterovirus and polyomavirus findings suggesting their occurrence often in asymptomatic subjects. No clear association with age was found although overall findings appeared to be more common in older children. Due to limited number of studies with repetitive samples, no clear conclusion can be drawn on the significance of PCR positive virus findings in asymptomatic subjects. The available reports, however, support the view that PCR is likely to detect true respiratory infections with or without symptoms. Asymptomatic innocent carriage may not exist. A major clinical question at the time of emerging respiratory viral infections is to what degree asymptomatic cases are infectious.