Bioaerosols and Disease

Airborne contaminants in the workplace can include chemical, physical, and biological agents. Although the primary focus of the industrial hygienist and toxicologist in the past has been on the health effects of chemical and physical contaminants, there is renewed interest in the science of “aerobiology”—the study of airborne particles of biological origin. Millions of workers in hundreds of occupations are exposed to potential health hazards in their workplace because of substances they breathe in the air. Every year, an estimated 65,000 U.S. workers develop respiratory disease related to their jobs, and an estimated 25,000 persons die from occupational lung disease. Respiratory illness causes an estimated 657 million person-days of restricted activity and 324 million person-days of lost work. Occupational exposure to airborne particles (aerosols) is very common and may pose a potential hazard to human health because microbial cells are particulate matter, studies that deal with airborne microorganisms are concerned with aerosols. Many of the physical and chemical processes that describe aerosol behavior also apply to bioaerosols. The term bioaerosol is used to describe a colloidal suspension of liquid droplets or solid particles in air, that contain or have attached to them one or more living or dead organisms, certain products of bacterial and fungal metabolism, or other biological material. Bioaerosols are ubiquitous indoors and outdoors and may contain cell fragments, dust mites, animal dander, skin scales, and a wide variety of microscopic organisms, including bacteria, viruses, fungi, algae, amoebae, and protozoa. Other nonliving biological substances (e.g., cotton dust, pollen, hemp, jute, sugarcane) also produce respiratory illness in workers. These are not considered in this chapter but have been reviewed elsewhere. This chapter focuses on those bioaerosols most likely to be related to the workplace, although nonoccupational sources can be prevalent. Bioaerosols such as house dust mites, animal dander, or cockroach products that are very important in inducing diseases like asthma may be referred to but are not discussed in detail because of their strong association with the home environment. Attention is given to infectious agents (and their products) because many working conditions are conducive to transmitting of such agents. Although bioaerosols generally represent fewer hazards than those of a physical or chemical nature, there are certain occupations where the risk of such exposures may be more prevalent. Occupational settings of concern include agriculture, saw mills, textile manufacturing, meat and other food processing, biotechnology, research laboratories, waste disposal, construction, and health-care institutions. The extent of health problems caused by bioaerosols in the workplace is difficult to estimate partly because of the wide array of agents that evoke a variety of human responses. The workplace atmosphere may contain hundreds of different kinds of biological particles, both pathogens and nonpathogens, and today's technology cannot quantify all of them. The complexity is even greater because of the broad range of different types of industrial environments and because exposures are not often recognized until the workers experience illness. Understanding the cause and effect relationship associated with exposure to bioaerosols is a most difficult and vexing problem. Despite uncertainty about the magnitude of the health risk caused by exposure, the impact is appreciable and has been considered the largest single cause of morbidity. This chapter is intended primarily for those occupational health professionals who seek to understand the potential health risk of airborne biological agents in the workplace. It presents an overview of the basic concepts and methodologies useful in assessing the health effects of bioaerosols, including the (1) types and properties of bioaerosols; (2) sources of bioaerosols; (3) transmission, infections, and disease; (4) interaction with environmental and physiological factors; (5) health effects from the inhalation of bioaerosols; (6) sampling and identifying airborne microbial contaminates; (7) assessment of risk; and (8) control and prevention of airborne infectious disease. Keywords: Bioaerosols; Bacteria; Viruses; Fungi; Rickettsias; Nonliving contaminants; Sources; Transmission; Infection; Disease; Contributing factors; Workplace; Allergies; Sampling; Identification; Risk assessment; Control; Prevention