With the use of our prediction rule, the PPV for identifying a child with a documented viral URI (75%) was similar to that found in other studies in both pediatric patients and adults using a variety of detection methods (6, 24, 25) . In these previous studies, the estimated PPV may actually have been somewhat inflated because there was no baseline viral screening. Thus, in prior studies, a proportion of the viruses detected could potentially be related to prolonged shedding rather than as the cause of symptoms (26) . In our study, 8.7% of viruses detected during an acute episode had been present at baseline without a significant increase in viral load.