Virus titers of airborne H9N2 AIV in an isolator. Air samples were collected simultaneously from the space of two isolators using an AGI-30 liquid sampler operated continuously for an optimized time of 30 min at an airflow rate of 12.5 L/min. Virus titer in the air was expressed as values of EID50/L air. Each color bar represented the every recombinant virus concentration in the air collected every two days from the beginning of 2 dpi in an independent experiment. No airborne virus was detected in the experiment for r01/NASS and r01/NA381 viruses.