Building-related illnesses are those for which there is a clinically defined illness of known etiology. These include infections such as legionellosis and allergic reactions such as hypersensitivity diseases and are often documented by physical signs and laboratory findings. Building-related illnesses are uncommon and are more serious in prognosis than mere discomfort. Physician diagnosis by clinical investigation of symptoms is the usual means of recognizing them. These illnesses can have a long latent (or asymptomatic) period after exposure begins before symptoms are experienced, similar to lung cancer after indoor radon exposure. Other categories of building-related illnesses, however, are associated with an immediate appearance of symptoms after exposure. They include toxic illness such as carbon monoxide poisoning; infectious diseases such as Legionella or Legionnaires' disease; and allergic disease such as asthma, hay fever, or hypersensitivity pneumonitis.
Building-related illnesses generally require a prolonged recovery time or may become a chronic problem for the patient, even after removal or remediation of the building exposure that caused the illness in the beginning. According to the Centers for Disease Control and Prevention (CDC), an estimated 8,000 to 18,000 people get Legionnaires' disease in the United States each year. Though an outbreak of this disease often gets media attention, most cases are isolated. If outbreaks do appear, they usually do so in the summer or early fall, though the disease can occur at any time of the year. Legionella has been found in air humidifiers and air-conditioning cooling towers, but not window air-conditioners or car air-conditioning units.
Asthma, a serious disease that makes breathing difficult, is the most common lung disease associated with indoor air pollutants. During the past two decades, a time when poor indoor air quality has been recognized as a potentially serious health hazard, the number of people with asthma has significantly increased. For example, in the United States, the number of people with asthma increased by more than 150 percent from 1980 to 1998 and affects an estimated 17 million Americans, including nearly 5 million children. The number of deaths due to asthma also has increased to almost 5,000 per year. According to the World Health Organization, between 100 and 150 million people worldwide - roughly the equivalent of the population of the Russian Federation - have asthma, with deaths reaching more than 180,000 annually.