From the earliest historic times men have believed that weather and climate influence human health and behavior. Sufficient data now exist to assume that some association exists between weather, climate, and many of the infectious diseases, as well as some of the chronic diseases such as arthritis. Changes in the prevalence or severity of these diseases are found, with varying degrees of regularity, to be associated with particular times of the year or types of weather. Weather and climate may be important in producing these variations, but the manner in which they act is not clear. The physiology of the individual may be affected, altering resistance to disease; in the case of infectious diseases, the mode of transmission may be modified; or the association may be indirect, due to altered habits of the populace.
It is difficult to determine the influence of meteorological changes on specific diseases; it is even