Environmental Engineering Reference
In-Depth Information
When exposure is chronic, hypersensitivity pneumonitis is characterized
by irreversible lung tissue damage, with progressive shortness of breath,
cough, malaise, weakness, anorexia, and weight loss. Hypersensitivity pneu-
monitis occurs mostly in adults and has been linked to a number of occu-
pations. Malt worker's lung, cheese washer's lung, farmer's lung, and bagas-
sosis are forms of hypersensitivity pneumonitis.
Outbreaks of hypersensitivity pneumonitis have been reported in a vari-
ety of building environments. These have been associated with contaminated
components of heating, ventilating, and air-conditioning systems (including
condensate drip pans and ductwork) and a variety of moldy materials.
Hypersensitivity pneumonitis appears to be caused by exposures to very
high levels of bacterial (thermophilic actinomycetes) spores or relatively
small (<3
m) mold spores that are deposited in lung alveolar tissue, causing
inflammatory responses and tissue damage.
µ
II. Bacteria and viruses
Bacteria and viruses, because of their small size, readily become airborne
and remain suspended in air for hours. The presence of bacteria has been
confirmed by air sampling; the presence of viruses is inferred from the spread
of respiratory infections. Airborne bacteria and viruses in indoor spaces are
of concern because they may transmit infectious diseases such as tuberculosis
(TB), meningitis, influenza, and colds. Bacterial endotoxins may also pose
significant exposure and health concerns.
A. Bacteria
Bacteria are single-celled organisms that are characterized by their lack of a
true nucleus and their relatively small size. They reproduce by simple fission.
Bacteria vary in size and shape. In bacterial species that have historically
characterized this group of organisms, cells assume three distinct morpho-
logical shapes: spherical (coccus), rod-shaped (bacillus), and spiral/curved
(spirillum, spirochete, vibrio). Species in the actinomycetes, sometimes called
the higher bacteria, form branching, very slender filaments and, in some
families, produce fungal-like mycelia. The “hyphae” of actinomycete species
break into spherical or rod-shaped segments that function as asexual spores.
Individual cells in the “lower bacteria” vary in size; coccoid bacterial
cells range from 0.4 to 2
µ
m; the smallest bacilli have a length of 0.5
µ
m and
a diameter of 0.2
µ
m; pathogenic bacilli have diameters no greater than 1 to
3
µ
m; nonpathogenic bacilli have diameters and lengths of up to 4 and 20
µ
m, respectively; spirilla typically have diameters of <1
µ
m with lengths
from 1 to 14
m.
Microscopic bacteria form colonies that can be easily seen with the naked
eye on culture media in relatively short periods of time (e.g., 24 hrs). The
“lower bacteria” look “slimy” or glistening; the actinomycetes look some-
what like fungi (
Figure 5.2
)
.
µ
