Infectious bacteria are transported by air. Droplet or infectious agents of 5 mm or less in size can remain airborne indefinitely. It has been shown that 90 to 95 per cent effective filters remove 99.9 per cent of all bacteria present in hospitals. Epidemiological evidence and other studies indicate that many of the airborne viruses that transmit infections are sub- micron in size, thus, there is no known method to effectively eliminate 100 per cent of the viable particles. HEPA filters or Ultra-Low Penetration (ULPA) filters provide the greatest efficiency currently available. Considering this, the isolation rooms with appropriate ventilation pressure relationships have provided to prevent the spread of airborne viruses in the hospital environment.

Treated Fresh Air (TFA) has a major role to play in hospitals. Outdoor air in comparison to room air is virtually free of bacteria and viruses. Infection control problems frequently involve a bacterial or viral source within the hospital. Ventilation air dilutes the viral and bacterial contamination within the hospital. Properly designed, constructed and maintained ventilation systems preserve the correct pressure relationship between functional areas; they remove airborne infectious agents from hospital environment. Fresh air at a rate of 15 CFM per person have provided in all rooms and care has been taken that same amount of air get extracted through toilets fans all times so that there is a continuous air change in the premises.