Airborne transmission refers to situations where smaller droplet nuclei or dust particles containing the pathogen can remain suspended in air for long periods of time (2 hours or more), and can travel a much greater distance from the patient, since they stay suspended longer. Patients with COVID-19 and other airborne transmissible diseases require negative pressure rooms. Other diseases exhibiting airborne transmission include TB, chicken pox (varicella), and measles. These diseases are much more transmissible than droplet, and a higher level of respiratory protection is needed. NIOSH recommends N95 respirators that have been properly fit-tested for all personnel caring for COVID-19 patients (see below).