Unifying concepts underlying the effects of organic dust exposures

A 5-year follow-up study on respiratory disorders and lung function in workers exposed to organic dust from composting plants

OBJECTIVES

To evaluate acute and chronic effects of long-term exposure to organic dust on respiratory disorders and lung function among employees at 41 composting facilities in Germany.

METHODS

A total of 218 compost workers and 66 control subjects were enrolled in the cohort. They were evaluated using a standardized questionnaire, a clinical examination, and spirometric measurements. Changes of symptoms, respiratory disorders, and lung function were determined in a first survey after 5 years of exposure in 123 compost workers and 48 controls. Exposure measurements were performed at six composting facilities for respirable dust, cultivable microorganisms, and endotoxins.

RESULTS

Exposure measurements revealed high concentrations of thermo-tolerant/thermophilic actinomycetes and filamentous fungi in the bio-aerosols at the composting sites. A significantly higher job fluctuation was observed among the compost workers compared to control subjects (95 vs. 18; p < 0.05). Compost workers reported a significantly higher prevalence of mucosal membrane irritation (MMI) of the eyes and upper airways than control subjects. Conjunctivitis was diagnosed significantly more often in compost workers. Forced vital capacity in percent of predicted (FVC%) of the non-smoking compost workers declined significantly (-5.4%) during the observation period compared to control subjects. The decline of FVC% in 16 compost workers exceeded 10% of initial values. A significant increase was observed in the number of compost workers suffering from chronic bronchitis (RR = 1.41; 95% CI = 1.28-1.55). Allergic alveolitis was diagnosed clinically in two compost workers.

CONCLUSIONS

The exposure to organic dust at workplaces of composting facilities is associated with adverse acute and chronic respiratory health effects, including MMI, chronic bronchitis, and an accelerated decline of FVC%. The pattern of health effects differs from those at other workplaces with exposures to organic dust possibly due to high concentrations of thermo-tolerant/thermophilic actinomycetes and filamentous fungi at composting plants.

Tumor necrosis factor-alpha hyper-responsiveness to endotoxin in whole blood is associated with chronic bronchitis in farmers

Many farmers experience chronic bronchitis, airflow obstruction, and asthma. It is thought that these respiratory problems may be related to workplace inhalation of organic dust containing endotoxin. The purpose of this study was to determine whether whole blood cytokine responsiveness to endotoxin is associated with airflow disorders (i.e., airflow obstruction, chronic bronchitis, and doctor-diagnosed asthma). Farmers (N = 95) were recruited from a rural cohort study and completed a respiratory symptom and history questionnaire, spirometry, and blood sampling. Blood was incubated 24 hours in the presence and absence of endotoxin and supernatants were analyzed for TNF-alpha, IL-1beta, IL-6, and IL-8. Hypo- or hyper-responsiveness to endotoxin was based on whether cytokine values were in the lower or upper 10% of the group range, respectively. A significant association existed between TNF-alpha hyper-responsiveness and chronic bronchitis. These results indicate that the whole blood cytokine assay may be useful to identify individual responsiveness to endotoxin, and may provide an additional diagnostic tool to evaluate persons potentially at risk for developing chronic bronchitis following exposure to organic dust in the workplace.

Environmental control for fungal allergen exposure

With our limited knowledge of the mold allergens, we must rely on common sense to reduce environmental exposure for patients who are allergic to mold. We understand that the first step is moisture control. Appropriate building design, keeping rainwater and ground water away from the interior, accomplishes this. In addition, the heating ventilation and air conditioning system must be appropriately designed and maintained. Functional maintenance of inside water sources such as free water from plumbing, appliances, and showers can prevent damaging leaks. Indoor humidity or water vapor must be controlled and maintained to prevent condensation on walls or in microenvironments, such as attics, bedrooms, basements, and beneath wall-to-wall carpeting. Few abatement trials have been published, but several suggest that such measures can reduce mold exposure.

Effects of bioaerosol polluted outdoor air on airways of residents: a cross sectional study

BACKGROUND

Bioaerosol pollution of workplace and home environments mainly affects airways and mucous membranes. The effect of environmental outdoor residential bioaerosol pollution, for example, livestock holdings, farming, and waste disposal plants, is unclear.

AIMS

To investigate the perceived health of residents living in areas with measurable outdoor bioaerosol pollution (for example, spores of Aspergillus fumigatus and actinomycetes), and effects of accompanying odours.

METHODS

In a cross sectional study, double blinded to ongoing microbial measurements, doctors collected 356 questionnaires from residents near a large scale composting site, and from unexposed controls in 1997. Self reported prevalence of health complaints during the past year, doctors' diagnoses, as well as residential odour annoyance were assessed. Microbiological pollution was measured simultaneously in residential outdoor air.

RESULTS

Concentrations of >10(5) colony forming units of thermophilic actinomycetes, moulds, and total bacteria/m(3) air were measured 200 m from the site, dropping to near background concentrations within 300 m. Positive adjusted associations were observed for residency within 150-200 m from the site versus unexposed controls for self reported health complaints: "waking up due to coughing", odds ratio (OR) 6.59 (95% confidence interval (CI) 2.57 to 17.73); "coughing on rising or during the day", OR 3.18 (95% CI 1.24 to 8.36); "bronchitis", OR 3.59 (95% CI 1.40 to 9.4); and "excessive tiredness", OR 4.27 (95% CI 1.56 to 12.15). Reports of irritative airway complaints were associated with residency in the highest bioaerosol exposure, 150-200 m (versus residency >400-500 m) from the site, and period of residency more than five years, but not residential odour annoyance. Lifetime prevalence of self reported diseases did not differ with exposure.

CONCLUSIONS

Bioaerosol pollution of residential outdoor air can occur in concentrations found in occupational environments. For the first time residents exposed to bioaerosol pollution were shown to report irritative respiratory complaints similar to mucous membrane irritation independently of perceived odours.

Indoor mold, toxigenic fungi, and Stachybotrys chartarum: infectious disease perspective

Damp buildings often have a moldy smell or obvious mold growth; some molds are human pathogens. This has caused concern regarding health effects of moldy indoor environments and has resulted in many studies of moisture- and mold-damaged buildings. Recently, there have been reports of severe illness as a result of indoor mold exposure, particularly due to Stachybotrys chartarum. While many authors describe a direct relationship between fungal contamination and illness, close examination of the literature reveals a confusing picture. Here, we review the evidence regarding indoor mold exposure and mycotoxicosis, with an emphasis on S. chartarum. We also examine possible end-organ effects, including pulmonary, immunologic, neurologic, and oncologic disorders. We discuss the Cleveland infant idiopathic pulmonary hemorrhage reports in detail, since they provided important impetus for concerns about Stachybotrys. Some valid concerns exist regarding the relationship between indoor mold exposure and human disease. Review of the literature reveals certain fungus-disease associations in humans, including ergotism (Claviceps species), alimentary toxic aleukia (Fusarium), and liver disease (Aspergillys). While many papers suggest a similar relationship between Stachybotrys and human disease, the studies nearly uniformly suffer from significant methodological flaws, making their findings inconclusive. As a result, we have not found well-substantiated supportive evidence of serious illness due to Stachybotrys exposure in the contemporary environment. To address issues of indoor mold-related illness, there is an urgent need for studies using objective markers of illness, relevant animal models, proper epidemiologic techniques, and examination of confounding factors.

Health complaints and immunological markers of exposure to bioaerosols among biowaste collectors and compost workers

OBJECTIVES

In a cross sectional study, work related health complaints and diseases of 58 compost workers and 53 biowaste collectors were investigated and compared with 40 control subjects. Levels of specific IgG antibodies to moulds and bacteria were measured as immunological markers of exposure to bioaerosols.

METHODS

With a standardised protocol, the participants of the study were interviewed for work related symptoms, conditions of exposure to bioaerosols at their workplaces, exposure to bioaerosols from other sources, atopic diseases, and smoking habits. They were clinically examined by physicians specialised in occupational medicine. Also, concentrations of specific IgG antibodies against antigens of moulds and actinomycetes occurring regularly at these workplaces were measured and compared with the health complaints of the workers.

RESULTS

Compost workers had significantly more symptoms and diseases of the airways (p=0.003) and the skin (p=0.02) than the control subjects. Health complaints of biowaste collectors did not differ significantly from those of the control group. Subjects with atopic diseases were underrepresented in the compost workers (p=0.003). Significantly increased antibody concentrations against fungi and actinomycetes were measured in workers at composting plants. The concentrations in biowaste collectors did not differ significantly from those in the control subjects. A significant association between the diseases and increased antibody concentrations were found in the compost workers.

CONCLUSION

The high exposure to bioaerosols of compost workers is significantly associated with a higher frequency of health complaints and diseases as well as higher concentrations of specific antibodies against moulds and actinomycetes. A healthy worker effect is indicated by the underrepresentation of atopic diseases among the compost workers compared with biowaste collectors and the control group.

Evaluation of chronic respiratory effects in the potato processing industry: indications of a healthy worker effect?

OBJECTIVE

To investigate the occurrence of chronic respiratory effects of exposure to organic dust in the potato processing industry.

METHODS

Self reported chronic respiratory symptoms and spirometric lung function were assessed in a cross sectional study among 135 potato processing workers. A comprehensive study of current exposure to dust, endotoxin, and potato antigens had been performed previously. Workers were grouped into low and high exposure categories for each of the three exposure indices. Relations between exposure concentrations and respiratory health variables were investigated either by calculating prevalence rate ratios or by performing linear regression analyses. Atopy was assessed by measuring total immunoglobulin E (IgE) and specific IgE to five common aeroallergens in serum samples of workers.

RESULTS

Evident relations between current exposure indices and respiratory health in the entire group were not found. Workers employed < or = 5 years showed a two-fold higher prevalence of respiratory symptoms, lower lung function, and higher endotoxin exposure than workers employed for > 5 years. Also, atopy was more prevalent in workers employed < or = 5 years. After stratification for duration of employment, negative effects of endotoxin on lung function among workers employed < or = 5 years were suggested.

CONCLUSIONS

This study does not show chronic respiratory effects of exposure to organic dust in the potato processing industry, despite the fact that the levels of exposure to endotoxin found in this industry have been reported to be associated with decreases in lung function in other occupational settings. A likely explanation for not detecting apparent effects might be that many symptomatic workers drop out of this industry a few years after starting the job, suggesting a healthy worker effect.

Concentration- and time-dependent upregulation and release of the cytokines MIP-2, KC, TNF, and MIP-1alpha in rat alveolar macrophages by fungal spores implicated in airway inflammation

Inhalation of fungal spores has been shown to cause primary or secondary infection and respiratory inflammation and diseases such as allergic alveolitis, atopic asthma, and organic dust toxic syndrome, which are rarely reported in the absence of predisposing factors. Biochemical and molecular markers of inflammation were measured in rat bronchial alveolar lavage cells (> 95% macrophages) following stimulation with fungal spores isolated from pathogenic and nonpathogenic fungi that have been implicated in airway inflammation. The results of this study demonstrate that mRNA transcripts for the C-X-C branch of the PF4 superfamily are differentially upregulated over those of the C-C mediators in a time- and concentration-dependent manner. Macrophage inflammatory protein (MIP)-2 and KC were differentially upregulated over the acute phase inflammatory cytokines MIP-1alpha and tumor necrosis factor-alpha (TNF-alpha) in rat alveolar macrophages stimulated with fungal spores from Aspergillus candidus, Aspergillus niger, Eurotium amstelodami, and Cladosporium cladosporioides. Spores from Aspergillus terreus and Penicillium spinulosum failed to stimulate an increase of any cytokine mRNA, whereas those from Aspergillus fumigatus stimulated the upregulation of MIP-2, KC, TNF-alpha, and MIP-1alpha mRNAs. Over time, A. fumigatus stimulated increasing KC production until 24 h, when production levels increased slightly, then leveled off when measurements ceased at 36 h. Latex spheres stimulated modest amounts of MIP-2 and transforming growth factor-beta only. These observations suggest that the inflammatory cytokines MIP-2 and KC may be involved in the inflammation arising from the inhalation of fungal spores in a time- and concentration-dependent manner.

Agents in organic dust: criteria for a causal relationship

Identification of agents of disease causation in organic dust is complicated by the fact that multiple agents may be involved, and these agents may act in a synergistic or additive fashion and cause a number of conditions resulting from chronic toxic or inflammatory effects. A new systematic approach to evaluating available data for evidence of disease-causing agents in organic dust is proposed. It combines, in a matrix fashion, principles of Koch's postulates, River's postulates, principles of epidemiologic determinants, and weight of evidence theory. By applying these principles in a systematic fashion, the strength of the scientific evidence for a specific agent can objectively be evaluated.

Methods for survey and diagnosis

This contribution is an overview of current epidemiologic methods used in evaluating organic dust-containing environments for evidence of adverse pulmonary effects. Potential problems include vague diagnostic criteria of "disease" and inadequate tools for definitive diagnosis, as illustrated by asthma and hypersensitivity pneumonitis. The enthusiastic investigator may consider trivial changes indicative of real or potential disease, and add the studied environment to a growing list of menaces of the workplace or of everyday life. Attention to scientific principles is needed lest epidemiology becomes scare-mongering made respectable by sophisticated statistics.