Airborne precautions must be used to prevent the transmission of airborne pathogens, that is, infectious agents that can be transmitted through small droplets suspended in the air. Patients infected with such pathogens must be isolated in an airborne infection isolation room or a single room with a negative-pressure ventilation system. It is also advised to keep the doors closed and limit the movement of such patients outside their rooms. To control the source of infection, patients must wear a mask and follow cough etiquette. A healthcare professional or a visitor entering the room should don properly fitting PPE, especially an N95 respirator. Depending on the type of infection, a person who has unprotected contact with the patient may be immediately immunized as a precaution. Protective environment precautions are used for immunocompromised patients, such as those who receive organ transplants or chemotherapy. Since such patients are vulnerable to infections, they must be kept in a specialized room with positive airflow ventilation and high-efficiency particulate filtration—greater than twelve air exchanges per hour. Additionally, the patient must wear a mask when out of their room.