Background: Children with acute respiratory tract infection (ARTI) frequently exhibit viral-viral codetection, yet its clinical significance remains contentious. Using data from a prospective cohort of children with influenza-like illness, we described the virology of ARTI and determined the clinical impact of viral-viral co-detection.Methods: Children aged 6-59 months presenting to a tertiary paediatric hospital with fever and acute respiratory symptoms were enrolled and nasal samples collected during influenza seasons in 2008-2012. Respiratory viruses were identified by culture and PCR. We compared demographics, presenting symptoms and clinical outcomes of children with single viral infection and viral-viral co-detection. We used logistic regression models and estimated marginal means to calculate the adjusted odds ratio and probabilities of symptom presentation, antibiotic prescription or hospitalisation.Results: 1630 of 2356 children (69.2%) had a virus detected, among whom rhinovirus (40.8%), influenza (29.5%) and respiratory syncytial virus (RSV; 26.4%) were most commonly detected. 24% of these had two or more viruses detected. After adjusting for demographic factors, children with co-detection had greater odds of presenting with cough (aOR=1.9, 95% CI:1.2-3.1), rhinorrhoea (aOR=1.8, 95% CI:1.1-2.9) than those with single infection, although both symptoms were common. Children with influenza and RSV combined had the highest probability of hospitalisation (probability=55%, 95%CI:35-73%), significantly greater than those with influenza infection alone (probability=22%, 95%CI:16-29%).Conclusions: Overall, co-detection has limited impact on clinical severity among children with influenza-like illness. However, specific pathogen pairs may be associated with more severe outcomes. Routine diagnostics to identify viral co-detection should be<br/
