Time Connection

It may be useful to establish a clear temporal association between symptoms and exposure, but it is also necessary to understand that in certain cases current exposures need not always result in immediate symptoms. For instance:

• It may be months before a car painter starts experiencing a dry hacking cough which presents itself during or after work. He may be suffering from bronchospasm due to toluene diisocyanate (TDI) exposure, a commonly used sensitizing agent, which is present in the car lacquer that the painter sprays. In case of allergic reactions, it may be months before clinical allergy and sensitization occurs. Once the asthma develops, there may be instances when symptoms extend beyond the work hours, and then be triggered by a wide range of irritants.
• Symptoms associative of hyperreactive airways (persistent shortness of breath and dry cough) can develop after a single, high-level exposure to an irritant, for instance sulfur dioxide or chlorine gas. This is referred to as “reactive airways disease syndrome” or “RADs”. Some rescue workers and firefighters who were exposed to a range of inhaled substances during and after the World Trade Center incident developed persistent bronchial hyperreactivity and severe cough.

During the early course of illness, symptoms associated with current exposures may get better on non-work days or during vacations, something that is indicative of the potential association to work. However, long-term exposure can make the symptoms persist beyond the weekdays. For instance, cases wherein a stitcher experiences aching in the wrist and hand caused by repetitive wrist flexion and pinching may initially get better with rest during the evenings or weekends. After the development of chronic tendonitis and carpal tunnel syndrome, the symptoms may extend beyond work hours and be worsened by other activities such as gardening or sewing. Moreover, other diseases, for instance asbestosis or cancer can occur with a long latency (ranging from 15 to 30 years from the actual exposure to the development of the disease).

Specific diagnoses, referred to as “sentinel health events” (SHE), are more prone to be associated with existing or past jobs. A SHE (occupational) is described as a disease, disability or ill-timed death which is associated with occupation and whose development may provide the momentum for analysis and interventions to prevent future cases. An individual who has been diagnosed with a SHE, for instance asthma, pulmonary tuberculosis, bladder cancer, contact dermatitis, pulmonary fibrosis, or peripheral neuropathy, would necessitate taking a more thorough occupational/environmental history in order to identify probable underlying (preventable) exposures.

The development of an illness in a person belonging to the low-risk category (for instance, occurrence of lung cancer in a non-smoker) can also prompt the clinician to focus more on the potential occupational or environmental exposures. In other cases, home or work exposures may seem to aggravate the underlying medical illness. Symptoms that do not have a clear etiology act as additional reasons to look for toxicological etiologies.