Many different plant components, such as pollen, fungal spores, and other particulates, have been found in the desert dust of southern Arizona. In addition to those which have already been noted by other workers as ingredients of the local dust, the present report includes 17 previously unreported pollens and the spores of 40 different genera of fungi. Several of these constituents are important to Arizona residents as causes of allergies. Others have not yet been shown to be allergenic, but their presence in dust indicates their potential significance in allergy.

Sixteen species of fungi known to be involved as agents of human disease, other than allergy, have also been identified in the soil surface dust of Arizona. Some are associated with diseases of the skin, hair, and nails, while others affect the lungs and other internal organs. A few of these are capable of causing life-threatening disease in several hundred individuals annually.

One of the most important dust-borne disease organisms in Arizona is Coccidioides immitis, the fungus that causes valley fever in man and certain animals. More than 27 human deaths each year have been caused by this organism in Arizona alone. Of 281 dust samples tested from the Phoenix area, 37 yielded the disease-producing fungus. It has also been found in dust analyzed from several other cities in the state. Increases in the incidence of valley fever in man following severe dust storms illustrates the importance of this mechanism in spore dispersal.

The loss in personal income and the medical care costs each year due to valley fever in its endemic area are estimated conservatively at $320 million. The effects of other pathogenic fungi, in combination with dust-borne pollen and other plant particulates, result in the loss of many times this amount annually.