Latency between exposure and disease
Many inhaled agents cause symptoms at the time of exposure. These include ‘Type I’ allergens (those that provoke an immediate response, although they may also lead to a delayed response) and irritative agents. Latent periods of about 8–16 hours after exposure may occur in patients with toxic pulmonary oedema and extrinsic allergic alveolitis (hypersensitivity pneumonitis). At the other extreme, slow accumulation of mineral dusts may lead to disease symptoms many years later. Occupational respiratory cancer after exposure to carcinogens mostly occurs after a latent period of at least 10 years. With malignant mesothelioma, the latency is up to 50 years and, consequently the peak incidence of this disease has not yet been reached (figure 2).