PERSPECTIVES Mycobacterial Aerosols and Respiratory Disease Joseph O. Falkinham, III* Environmental opportunistic mycobacteria, including disinfectant treatment of the waters or fluids to reduce the Mycobacterium avium, M. terrae, and the new species M. number of microorganisms. Living or working in water- immunogenum, have been implicated in outbreaks of damaged buildings or as a consequence of reconstruction hypersensitivity pneumonitis or respiratory problems in a of water-damaged buildings has also been associated with wide variety of settings. One common feature of the out- outbreaks of respiratory problems (8,9). Respiratory dis- breaks has been exposure to aerosols. Aerosols have been ease has been associated with mycobacteria in reservoirs, generated from metalworking fluid during machining and aerosols, or structural material in a number of cases grinding operations as well as from indoor swimming pools, (2,3,6,7,9). hot tubs, and water-damaged buildings. Environmental opportunistic mycobacteria are present in drinking water, Hypersensitivity Pneumonitis in Workers resistant to disinfection, able to provoke inflammatory reac- Exposed to Metalworking Fluid tions, and readily aerosolized. In all outbreaks, the water An estimated 1.2 million workers in the United States sources of the aerosols were disinfected. Disinfection may are exposed to aerosols generated by metal grinding (10). select for the predominance and growth of mycobacteria. Metalworking fluids are widely used in a variety of com- Therefore, mycobacteria may be responsible, in part, for mon industrial metal-grinding operations to lubricate and many outbreaks of hypersensitivity pneumonitis and other cool the tool and the working surface. Metalworking fluids respiratory problems in the workplace and home. are oil-water emulsions that contain paraffins, pine oils, polycyclic aromatic hydrocarbons, and heavy metals (10,11). Exposure to metalworking fluid aerosols can lead ypersensitivity pneumonitis is an occupational hazard to hypersensitivity pneumonitis and chronic obstructive of workers in two different industries, automobile H pulmonary disease (1,6,12–14). Mycobacteria were recov- manufacturing (e.g., metal working) and leisure (e.g., ered significantly more frequently from metalworking indoor swimming pools). Pulmonary illness and infection fluid samples collected from facilities where hypersensi- have also been a consequence of exposure to aerosols gen- tivity pneumonitis was found; compared to facilities that erated by hot tubs, spas, and coolant baths. Respiratory did not have hypersensitivity pneumonitis (6). In one problems have also been associated with exposure to study, exposure to metalworking fluid mist resulted in water-damaged buildings during reconstruction, and hypersensitivity pneumonitis in 10 workers (7). Acid-fast mycobacteria isolated from materials from such buildings microorganisms identified as mycobacteria were present in have been shown to provoke inflammatory reactions. The the reservoir at 107 CFU/mL (7). A mycobacteria in the outbreaks share the common feature of aerosol exposure reservoir was considered to be a likely cause of the hyper- and respiratory illness. I propose that exposure to aerosols sensitivity pneumonitis because one patient was infected containing mycobacteria is a common feature of the out- by a Mycobacterium sp. and had antibodies against the breaks and that mycobacteria or their products could be reservoir fluid (7). responsible for the respiratory symptoms. Hypersensitivity pneumonitis appeared in spite of dis- Epidemiologic studies have established that the work- infection of the metalworking fluid with morpholine, ers in such outbreaks were exposed to aerosols generated formaldehyde, or quaternary ammonium-based disinfec- in the workplace from water that was either a work tool tants (1,6,12,13), and mycobacteria were recovered from (e.g., metalworking fluid) or an integral part of the work- the metal working fluid (6,14,15). Mycobacteria are resist- place or household (e.g., swimming pools and hot tubs) ant to formaldehyde and quaternary ammonium disinfec- (1–7). Outbreaks of respiratory disease occurred in spite of tants (16) and the heavy metals in metalworking fluids (17). Further, mycobacteria can grow on the organic com- *Virginia Polytechnic Institute and State University, Blacksburg, pounds in metalworking fluid, including the paraffins, pine Virginia, USA Emerging Infectious Diseases • Vol. 9, No. 7, July 2003 763 PERSPECTIVES oils, and polycyclic aromatic hydrocarbons (18,19) and relatively resistant to high temperature (29) and concen- can degrade the disinfectant morpholine (20). trated in hospital hot water systems (30). Mycobacteria present in the water (21) can likely grow on the organic compounds in metalworking fluids in the Hypersensitivity Pneumonitis in absence of competitors after disinfection. Cleaning would Occupants of Water-Damaged Buildings not be expected to eradicate mycobacteria because of their Inflammatory reactions—including eye irritation, res- ability to form biofilms (21,22). Adding disinfectant and piratory infections, wheeze, bronchitis, and asthma—in cleaning the reservoir in one facility did not prevent the workers in water-damaged or “moldy” buildings have been reappearance of mycobacteria (7 x 105 CFU/mL by 2 associated with the presence of high numbers of microor- weeks [7]). Further, disinfectant treatment would likely ganisms (8). Mycobacteria were recovered from materials result in selection of mycobacteria remaining after the collected from water-damaged buildings, as well as from cleaning. microorganisms normally associated with building materi- als (9). During reconstruction, those mycobacteria could Hypersensitivity Pneumonitis in be aerosolized in the dust. Although other microorganisms Swimming Pool Attendants could be responsible for the respiratory problems, both Granulomatous pneumonitis has been reported in life- saprophytic (e.g., M. terrae) and pathogenic (e.g., M. guards (“lifeguard lung”) who worked at an indoor swim- avium) strains isolated from moldy buildings were capable ming pool that featured waterfalls and sprays (5). Affected of inducing inflammatory responses in a mouse lifeguards with symptoms worked longer hours than unaf- macrophage cell line (31). The mycobacteria elicited dose- fected lifeguards (5), which demonstrated a dose-response dependent production of cytokines interleukin-6 and tumor effect. The waterfalls and sprays increased the number of necrosis factor-α, nitric oxide, and reactive oxygen species respirable particles fivefold and the levels of endotoxin from the murine macrophage (31). Because whole eightfold (5). Based on the presence of endotoxin in the mycobacterial cells were used in the assays (31), whether aerosol samples, endotoxin exposure was suggested as the cell metabolites, which are likely easily aerosolized, were cause of the pneumonitis in lifeguards (5). However, sub- responsible for the induction of inflammatory reactions is sequent data provided evidence of a possible second factor not known. Heat-shock proteins from a number of resulting in hypersensitivity pneumonitis; aerosols con- mycobacterial species have been shown to generate Th1- taining mycobacteria were shown to cause granulomatous type responses, airway inflammation, and airway hyperre- lung disease (4). Others have reported high numbers of sponsiveness (32). This evidence suggests that mycobacte- mycobacteria in swimming pools and whirlpools (23) and ria or their metabolites are possible causes of respiratory in hot tubs (2,3,24). Further, amoebae were reported in the disease in persons exposed to water-damaged buildings. indoor swimming pool where lifeguards reported pneu- monitis (5). Mycobacteria, including M. avium and M. Ecology of Mycobacteria intracellulare, can survive and grow in phagocytic amoe- The unique combination of physiologic characteristics bae (25) and protozoa (26). In fact, M. avium grown in that distinguish the environmental opportunistic mycobac- amoebae or protozoa are more virulent (25; Falkinham JO, teria make them likely agents for causing respiratory dis- unpub. data). Mycobacteria are resistant to chlorine (27) ease in these diverse settings. Mycobacteria are found in a and preferentially aerosolized from water (28). great variety of natural and human-influenced aquatic environments, including treated drinking water (21) and Mycobacterial Disease after Exposure to aerosols (33). Mycobacteria in drinking water are associat- Aerosols Generated by Hot Tubs ed with the presence of particulates (21). Although these Hypersensitivity pneumonitis and mycobacterial pul- microbes are grown in rich media in the laboratory, they monary disease has been reported after exposure to hot are oligotrophic and capable of substantial growth in low tubs (2,3,24). The mycobacteria isolated (e.g., M. avium) concentrations of organic matter. For example, M. avium were likely responsible for the infections based on the and M. intracellulare can grow in natural and drinking identity of patient and hot tub mycobacterial isolates by water over a temperature range of 10°C to 45°C (34). either restriction fragment length polymorphism analysis Mycobacteria are relatively resistant to high temperatures. (24) or multilocus enzyme electrophoresis (2,3). Further, For example, 10% of cells of a strain of M. avium survived exposure was followed closely by the onset of symptoms, after 1 h at 55°C (29). Mycobacteria are slow growing as a and