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
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
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
Some bacteria such as Legionella pneumophila are basically
and survive more readily in a humid environment. Codes and
guidelines specify temperature and humidity range criteria
hospital areas as a measure for infection control as well