This research has arisen from the need to understand the air patterns within isolation rooms and how they can affect the transmission of airborne diseases to staff or visitors who are inside the room with an infectious patient. Similarly, when it is the patient who needs protection from airborne infection, the ventilation patterns inside the room need to be understood in order to protect the patient. At times staff are very close to a patient and the risk of infection during these activities needs to be quantified. This study analyses the risk of infection in these cases, with different ventilation regimes. Differential pressures between an isolation room and adjacent spaces and airtightness levels also aid in preventing the transmission of infectious diseases, The existence of many different international guidelines with regards to ventilation flow rates, air changes per hour and differential pressures between rooms make the selection complicated for designers. This study investigates the effect that pressure differentials and airtightness have in infection control and how higher differential pressures, which are more difficult to achieve and maintain, impact on the protection. With the recent Ebola infection breakouts and fear of biological attacks, a new model for an isolation room for this type of pathogens (category 4) has been studied. The design intended to remove a patient's containment Trexler tent, in order to provide better access and care to the patient. Several changes to the original design have been studied in order to improve the ventilation in the isolation room. The risk of infection to staff in all variations of the design has been studied. Finally, engineering methods quantify airborne infection using tracer gas techniques, such as carbon dioxide or nitrous oxide, however little research has been done to compare the gas tracer techniques with the behavior of real bacteria