Do indoor molds in nonindustrial environments threaten workers' health? A review of the epidemiologic evidence.

Since the early 1980s, mucosal, skin, and respiratory symptoms, in addition to general symptoms such as fatigue and headache, have been related to the indoor climate of nonindustrial workplaces. Mold growth has been suggested as a causal factor because the health complaints frequently have been related to indicators of microbial contamination: visible signs of mold growth, moisture, and water damage (1). Molds refer to growing colonies of different species of fungi. Fungi are nonphotosynthetic plant bodies that are ubiquitous in nature and decompose organic material. The species differ in size, but most are about 10 μm in diameter. Fungi are able to grow at a relative humidity of between 75 percent and 95 percent at normal room temperature. Fungi reproduce by spores that spread by air, depending on climatic factors, activity in the surrounding environment, and physiologic properties of the individual species (2, 3). Growing fungi may produce metabolites to protect a nutrient source from bacteria. Mycotoxins are metabolites that are able to initiate a toxic response in vertebrates when ingested, inhaled, or otherwise absorbed. Mold antigens may induce an immunoglobulin E–mediated response (4, 5). β-(1,3)-D-glucan is a polyglucose structure of mold cell walls that can induce inflammatory reactions through a specific receptor (6, 7). Ergosterol is the primary membrane sterol of filamentous fungi, and extracellular polysaccharides are stable carbohydrates secreted during fungal growth. At present, there is no evidence for a pathogenic role of ergosterol or extracellular polysaccharides in allergic or inflammatory reactions to fungal components (8). High-level exposure to airborne mold spores may cause allergic alveolitis (e.g., farmer’s lung) (9). Aerosols from air humidifiers heavily contaminated by bacteria, algae, or molds may cause inhalation fever (humidifier fever) (10). Single cases of occupational asthma have been attributed to mold exposure (11, 12), and asthma severity has been associated with outdoor mold spore levels in children and adolescents (13). Mold-contaminated food and feed have been held responsible for serious cases of poisoning in humans and livestock (14). It was discussed recently whether mycotoxins may be responsible for cases of acute idiopathic pulmonary hemorrhage in infants (15, 16). Among employees of nonindustrial workplaces with visible signs of mold growth, moisture, or water damage, there has been an increasing concern about possible health effects. This review evaluates this concern based on present epidemiologic literature. Recently, the topic was partly reviewed by Husman, Verhoeff and Burge, and Peat and Dickerson (17–19). However, they focused mainly on the health effects in children, which may not be relevant for the adult working population (20). Furthermore, several studies assessing mold exposure in the sick building syndrome were included to only a limited extent. This is a systematic review of reports on health effects related to mold growth (or indicators of mold growth) in nonindustrial work sites. Since comparable mold exposure is seen in dwellings, studies that related adult health effects to exposure at home were also reviewed (21).