Bioaerosols - Aerosols: Measurement, Dosimetry, and Health Effects - page 307

12.3.2 b ioaerosols in tHe i ndoor e nvironMent
Exposure to inhalable aerosols containing infectious viruses or bacteria is more common in winter
when people spend more time indoors, ventilation rates are reduced, and ill persons cough and
sneeze in proximity to susceptible individuals.
12.3.2.1 Viruses, Bacteria, and Bacterial Endotoxin
Humans are the primary source of indoor viral pathogens, but very little is known about the aerody-
namic size of infectious virus particles. See Section 12.2.1.1 for a discussion of indoor transmission
of infectious viruses and bacteria.
Only a few studies have focused on bacteria in damp indoor environments. Some of these identi-
ied Streptomycetes species on damp or wet indoor surfaces or released from moisture-damaged
building materials. 175-177 Streptomycetes are Gram-positive, spore-forming actinobacteria that can
produce a wide range of metabolites including some toxins such as valinomycin. 178-182
Environmental mycobacteria also have been found to be common in moisture-damaged build-
ings, and their occurrence was shown to increase with an increasing degree of fungal damage. 183
Concentrations of total viable bacteria in indoor environments may range between 10 1 and 10 3 col-
ony-forming units (CFU)/m 3 . 184 These levels most likely represent the degree of building occupancy
and ventilation eficiency. From the literature it is not clear what “typical” bacterial air concentra-
tions are in damp versus non-damp indoor environments.
Endotoxins are composed of lipopolysaccharides (LPS) and lipooligosaccharides (LOS),
cell wall components of Gram-negative bacteria. Endotoxins are nonallergenic, with strong
pro-inlammatory properties. They are present in many occupational environments, ambient air, 185
and house dust. 13,68
Endotoxin concentrations in house dust range from a few to several thousand Endotoxin Units
(EU)/mg. 68 Concentrations expressed per square meter vary even more. Studies have found no
evidence for a positive relationship between endotoxin in house dust and observed dampness or
mold, 186-188 but a positive association was found between moldy odor and the concentration of air-
borne endotoxin. 189 Only a few studies have focused on indoor air concentrations, for example, a
mean airborne endotoxin concentration of 0.64 EU/m 3 was reported in 15 homes in Boston, MA
(mean dust concentration: 44-105 EU/mg). 190 The mean inhalable endotoxin concentration in nine
Belgian homes was similar, that is, 0.24 EU/m 3 . 191 Higher concentrations of airborne endotoxin were
measured in the Midwestern United States and New Orleans (geometric means, 4.2 and 3.0 EU/m 3 ,
respectively). 189,192
Animal and human toxicity tests with endotoxin and LPS have shown that inhaled endotoxin causes
inlammation with the release of different cytokines and increased production of oxygen metabolites.
Alveolar macrophages and bronchial epithelial cells are the primary targets; endothelial cell damage
also has been observed. The concentrations of cytokines peak a few hours after inhalation.
Subjects exposed to endotoxin in inhalation experiments experience clinical effects such as fever,
shivering, arthralgia, inluenza-like symptoms (malaise), blood leukocytosis, neutrophilic airway
inlammation, asthma symptoms (such as dry cough, dyspnea, and chest tightness), and bronchial
obstruction as well as dose-dependent lung function impairment (measured as FVC, FEV 1 , and
low-volume variables) and decreased lung diffusion capacity. 68 Subjects with increased bronchial
hyperresponsiveness or asthma may be more likely to develop symptoms when challenged with
endotoxin, but large differences in airway responsiveness to inhaled endotoxin also exist in healthy
(nonallergic) subjects. 193
Endotoxin has been suggested to play a role in nonoccupational respiratory disease, most nota-
bly asthma (Section 12.2.2.1). Several studies showed a positive association between endotoxin in
house dust and symptoms, lung function, and medication use in children with pre-existing asthma. 14
A positive association between indoor endotoxin and respiratory symptoms also has been reported
in infants 194 and adults. 13 In contrast, several other studies have suggested that domestic endotoxin