disease as the reason (Perks et al., 1979). Moreover, occupational diseases are generally underreported (I. L. Bernstein, 1981; NRC, 1987a). Although the annual incidence of work-related disease is believed to be approximately 20 per 100 population, one study (Discher et al., 1975) found that only 2 percent of illnesses were actually reported in employers' logs.

Allergic Diseases Caused by LMW Chemicals

The diseases caused by allergic reactions to LMW chemicals are similar to those caused by other, larger (i.e., high-molecular-weight, or HMW) allergens. More specifically, allergic diseases related to LMW chemicals include allergic rhinitis and conjunctivitis, hypersensitivity pneumonitis, asthma, late respiratory systemic syndrome (LRSS), and hemorrhagic pneumonitis. Scientists assume that chemicals act as allergens by forming haptens (covalently coupling) at multiple sites on the surface of a host carrier protein, which could be in the serum, airway, epithelium, or blood cells. Allergic rhinitis or allergic conjunctivitis, or both, may occur as a result. Allergic asthma can be immediate in onset, delayed, or both (Fink, 1982). The hypersensitivity pneumonitis that occurs as a result of exposure to chemicals in the workplace is generally of the acute type. LRSS is a related disease characterized by cough, chills, fever, and myalgias 4 to 12 hours after exposure (Zeiss et al., 1977). Workers with LRSS have high levels of antibody against TMA conjugated with human proteins such as human serum albumin (TM-HSA).

Another disease, hemorrhagic pneumonitis, is caused by immunologic reactions to chemicals such as TMA (Zeiss et al., 1977) and TDI (Table 3-4). For example, after significant exposure in a TMA-sensitized individual, a hemorrhagic pneumonitis and anemia known as pulmonary disease anemia (PDA) syndrome may occur (Patterson et al., 1978). These workers have very high levels of antibody against TM-HSA and very high levels of TMA exposure, usually from hot fumes. The anemia is likely to be an immune-mediated hemolytic type, probably because reactive chemicals like TMA couple easily with cells (they react readily with cell surface proteins). This process results in type II immunologically mediated cytotoxicity, a condition that cannot occur with complete allergens such as foreign proteins because they cannot react covalently with cell surface proteins (Patterson et al., 1979). There have also been reports of hemorrhagic pneumonitis without anemia caused by TDI (Patterson et al., 1990).

Chemical Agents That Cause Allergic Disease

A variety of pharmacologic agents have caused asthma among hospital and pharmaceutical workers when airborne dust is inhaled. Numerous antibiotics,

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