In this work, seven patients with onset flu symptoms (their medical information is listed in Table S2 , Supporting Information) were also recruited from the respiratory clinic of Peking University Third Hospital in Beijing. About 40 ml of exhaled breath condensate collected from each of 7 patients was diluted by 10 times and then plated on Trypticase Soy Agar (TSA) (Becton, Dickson and Company, Sparks, MD) plates at 26uC for 2-3 days, and colony forming units (CFUs) were manually counted. The total culturable bacterial aerosol concentration was calculated as CFU/m 3 (exhaled breath) by considering the collection time and an average breathing rate of 12 L/min for an adult. Besides, the culturable bacterial species were identified using VITEKH 2 (BioMérieux, Inc,100 Rodolphe Street, Durham, NC). In addition, molecular detection of bacteria and virus using qPCR and RT-qPCR, respectively, were performed according to the procedures described in Supporting Information S1. To further confirm the bacterial presence DNA stain of EBC sample by Acridine Orange (AO) was also conducted.