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Respiratory diseases include the mild forms of upper respiratory infection (the common cold),for which a doctor is not usually consulted, and the acute respiratory infections - influenza,pneumonia, etc.In the United States, the National Health Survey estimated that there were about 215 millionrespiratory illnesses per year, but other studies suggest there may actually be four to fivetimes that, or more than one billion such illnesses per year. Studies of respiratory diseasesin Europe have estimated that in many European countries, about one third of all sicknessabsenteeism in the working population were due to respiratory diseases (1).

The incidence of colds always rises at the beginning of September, and increases with fluctuations until January and February, then declines to lower levels in the spring. This cyclical variation which occurs in conjunction with changes in weather has been studied by many investigators. Although respiratory diseases are frequently blamed on changes in the weather and cold weather, the indoor atmospheric condition likely plays a more important role in the incidence of colds than that of the weather, because in industrial nations, 95% of the time is spent indoors (7).

This paper has assembled the results of six investigations by independent researchers indifferent countries.

Citation: Symposium, ASHRAE Transactions, Volume 85, Part 1, Philadelphia, PA