No virus was detected at baseline in 87 of the 108 children (80.6%) who had a nasal swab collected for an acute illness. Viruses detected at baseline in the remaining 21 children are shown in Table 3 . Five patients had rhinovirus detected at both baseline and with the acute nasal swab. In one child, there was Ͼ2 log increase in viral load from baseline to the acute swab; this patient was classified as having a viral URI. The other four patients had no substantial increase in rhinovirus load and were categorized as having no URI. In all other "positive" acute swabs, the virus detected had not been present at baseline. Overall, a respiratory viral etiology was identified in 62 of the 108 children (57.4%, 95% CI: 47.5-66.9%) considered to be developing a cold with at least one respiratory symptom (Table 3) . Rhinovirus was the most common etiologic agent, accounting for 49.2% of all viruses detected.