What are Bioaerosols as they relate to viruses, bacteria or fungus?
BIOAEROSOLS
Understanding Bioaerosols Germs, bacteria, viruses - the presence
of invisible and health-threatening life-forms has captured the imagination
and concern of the public at large, as well as scientific specialists,
for a good part of this century.
But only with the isolation of legionella bacteria as the cause of
serious illnesses and deaths at a hotel in Philadelphia, Pennsylvania,
did microbial infection come to light as a building- related issue.
VIRUSES
Beginning with viruses, we must remind ourselves that these organisms
are host-dependent - in the case of human pathogens, requiring people
in order to reproduce. By contrast, most bacteria and fungus can support
themselves on nonliving Environmental substrates.
Transmission modes vary for different viruses. The most frequently
encountered viral infections are colds and flus. For many of the viruses
there is debate in the public health community as to whether they
are transmitted principally by air or by physical contact. Many public
health officials favor the latter, in spite of the fact that the air
transfer model better explains empirical studies of infection patterns.
Influenza viruses tend to be transferred almost exclusively in the
air, whereas cold viruses are more complex, some of them transferred
by air, other strains - such as adenoviruses - by contact.
Viruses are extremely small, and filters tend to be insufficient for removing
them from the air. In the past, there was little data to show that any
environmental control method slows the spread of virulent contagious disease.
However, in the last 8 years many tests on ultraviolet light systems have
proven effective.
BACTERIA
In the realm of bacteria, chiefly legionella diseases and hypersensitivity
pneurnonitis, two illnesses are associated with the legionella bacterium.
The first, Pontiac Fever, is characterized by debilitating, though
not dangerous, flu-like symptoms. The symptoms are so much like influenza,
that it is probably undiagnosed in most cases, showing up only in
studies of severe building outbreaks. Once a building has been infected
with Pontiac Fever, 90%-95% of the people will be affected. Because
it is under-reported, little is known about how the bacterium causes
the illnesses, or what the associated risk factors might be.
The more serious illness linked to legionella is, of course, Legionnaire's
Disease. The rate of contracting the illness is very low with respect
to exposure, and little is known about what triggers the onset of
the disease, except that there are a number of risk population types
- heavy drinkers, smokers, and otherwise immuno-compromised individuals.
Legionella bacteria are commonly found wherever there are water reservoirs.
They become a threat to air quality only if entrained into the air
by the ventilation system.
Along with Legionnaire's Disease, there is hypersensitivity pneumonitis
(HP) as a serious, and preventable, illness traceable to airborne
microbial contaminants. Alternatively known as allergic alveolitis
or Farmer's Lung Disease, this illness is associated with a number
of common bacteria, as well as fungi, including Bacillus species.
While HP is not a common illness - induction tends to require substantial
doses - it may be induced by any number of antigens in the environment.
Once sensitized, an individual is vulnerable to low levels of that
antigen. One of the difficulties with tracing HP is that its manifestation
is irregular. Researchers are confident that there are risk factors
associated with the illness but do not know what they are.
FUNGUS
The principal health worries associated with fungus are the mycotoxins
- metabolic products, including aflatoxins produced by Aspergillus
flavus and the toxins produced by Stachybotris atra, among others
- and pathogenic spores. Most mycotoxins are associated with agricultural
settings, where fungal concentrations are significantly high.
While allergic diseases present the more common problem associated
with fungi and their products, exposure to mycotoxins is more worrisome
because of the compounds themselves. Mycotoxins are not volatile,
but they are concentrated in fungus spores and therefore become airborne
with the spores.
In addition, aerosolization of minute fragments of the substrate could
also bear toxin aerosols. Investigators should assume that the presence
of the organisms indicates the presence of the toxin as well, unless
specific tests prove otherwise. In general, fungal growth sufficient
to create dangerous levels of these mycotoxins will become apparent
in a walk-through inspection.
The greater concern with rnycotoxins and other potentially pathogenic
fungus products is that these minute particles may linger after you
remove fungal sources. Fungi produce spores in bursts and peak levels,
and the toxins can pass through filtration systems and remain suspended
in the air.
Other illnesses associated with fungus include hypersensitivity pneumonitis,
allergic rhinitis, and allergic asthma.
Histoplasmosis and cryptococcosis, both associated with concentrations
of bird droppings, do occur but are rare. Aspergillosis is a very
unusual but virulent illness, primarily of concern in environments
with immuno-compromised subjects, particularly in hospitals.
Fungus, like bacteria, generate volatile organic compounds (VOCS)
as metabolic byproducts. These compounds - which include ethanol,
other alcohols, and aldehydes - are responsible for the odors associated
with mold growth.
Research characterizing VOCs generated by microorganisms is scarce,
yet many of these gases may be causative irritants of SBS-type symptoms.
Many fungi utilize unusual substrates, often producing strange results.
As an example, a test showed a case of fungus on a treated surface containing
an arsenic compound. The fungus released arsine.
In addition to viruses, bacteria, and fungus, there are other biological
sources of indoor air pollution. Certainly the most familiar of these
is the dust mite, which thrives on human dander and whose feces are
antigens linked to allergic asthma. In addition to dust mite feces,
cockroach products and animal saliva and urine have been tied to asthma.
