Using a six-zone lung ultrasound scanning protocol similar to that described by Copetti et al. [7] , we defined and classified patients as positive or negative for viral pneumonia based on the presence of small subpleural consolidations usually <0.5 cm ( Figure 5 and Additional file 1) and/or individual B-lines or confluent B-lines (echogenic vertical lines arising from the pleural line to the bottom of the ultrasound screen; Figure 6 and Additional file 2) [7] . These ultrasound findings are similar to those described in interstitial syndrome which is defined as three or more B-lines in a given lung region [10, 14, 15] . A-lines (horizontal, reverberation artifacts of the pleural line; Figure 7 left) which indicate areas of the normal lung were also noted when present [10, 14] . Patients were classified as positive or negative for bacterial pneumonia based on the presence or absence of lung consolidation with air bronchograms [6, 7, 16] seen on ultrasound (Figures 7 right, 8, and Additional file 3). A clinical course with follow-up after 2 weeks (via electronic medical record and telephone interview) was used to determine disposition and outcomes of enrolled patients. Clinicians performing and interpreting ultrasound were blinded to chest X-ray results, and when performed per hospital protocol for possible admission, viral antigen testing results. Bacterial pneumonia on chest X-ray (posterior-anterior and lateral views) was classified based on the attending pediatric radiologist reading for 'consolidation, 'infiltrate, or 'pneumonia. For analysis purposes only, viral pneumonia on chest X-ray was defined as 'peri-bronchial cuffing, 'peri-bronchial thickening, or 'increased interstitial markings identified by the pediatric radiologist. Pediatric radiologists were blinded to the lung ultrasound results.