Any time the patient can cough or sneeze into the room – the  risk of infection is increased. Some model studies show that if there is a mask leak – the high flow from the ventilator to compensate for the leak may force particles out into the room.
During the 2003 SARS CoV-1 outbreak, many healthcare workers became infected due to failure to implement adequate infection control precautions especially when performing aerosol generating procedures (Tran et al. PloS One 2012). However, because of the limited number of studies reporting NIPPV use in SARS CoV-1, the risk of infection could not be established with certainty. Moreover, in a Singapore study of SARS CoV-1, institution of rigorous protective measures (including air-purifying respirator units) for over 200 healthcare workers resulted in zero cases of infection (Lew et al JAMA 2003).