Infection Sources and Control Measures
Bacterial Infection. Examples of bacteria that are highly infectious and transported within air or air and water mixtures are Mycobacterium tuberculosis and Legionella pneumophila (Legionnaire’s disease).

Wells (1934) showed that droplets or infectious agents of 5 mm or less in size can remain airborne indefinitely. Isoard et al. (1980) and

Luciano (1984) have shown that 99.9% of all bacteria present in a hospital are removed by 90 to 95% efficient filters (

This is because bacteria are typically present in colony-forming units that are larger than 1 mm. Some authorities recommend the use of high efficiency particulate air (HEPA) filters having dioctyl phthalate (DOP) test filtering efficiencies of 99.97% in certain areas.

Viral Infection. Examples of viruses that are transported by and virulent within air are Varicella (chicken pox/shingles),

Rubella (German measles), and Rubeola (regular measles).

Epidemiological evidence and other studies indicate that many of the airborne viruses that transmit infection are submicron in size; thus, there is no known method to effectively eliminate 100% of the viable particles.

HEPA and/or ultra low penetration (ULPA) filters provide the greatest efficiency currently available. Attempts to deactivate viruses with ultraviolet light and chemical sprays have not proven reliable or effective enough to be recommended by most codes as a primary infection control measure. Therefore, isolation rooms and isolation anterooms with appropriate ventilation-pressure relationships are the primary means used to prevent the spread of airborne viruses i the health care environment.

Molds. Evidence indicates that some molds such as Aspergillis can be fatal to advanced leukemia, bone marrow transplant, and other immunocompromised patients.

Outdoor Air Ventilation.

If outdoor air intakes are properly located, and areas adjacent to outdoor air intakes are properly maintained, 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 a hospital. If ventilation systems are properly designed, constructed, and maintained to preserve the correct pressure relations between functional areas, they remove airborne infectious agents from the hospital environment.

Temperature and Humidity. These conditions can inhibit or promote the growth of bacteria and activate or deactivate viruses. Some bacteria such as Legionella pneumophila are basically waterborne and survive more readily in a humid environment. Codes and guidelines specify temperature and humidity range criteria in some hospital areas as a measure for infection control as well as comfort.