Emergence of hantaviral disease in the southwestern United States.

Hantaviruses are parasites of small mammals, predominantly peridomestic and commensal rodents. They have a worldwide distribution. Hantavirus-related illness occurs in rural areas where humans come into contact with rodents. In most cases human infection is manifested by one of a variety of acute illnesses involving hemorrhagic fever and renal disease. In May 1993, a cluster of patients with an acute pulmonary disease with high mortality was noted in the Four Corners region of the southwestern United States. Serologic and genetic studies indicated that the etiologic agent was a novel hantavirus. The uncertainty engendered by the emergence of a new disease with high mortality forced a rapid response by state and federal agencies and by the University of New Mexico Medical Center, Albuquerque, where most patients from this region were referred. Considerable progress has been made in identifying infected cases on clinical and laboratory grounds and in ensuring that appropriate supportive care is made available to patients as soon as they are suspected of having hantaviral infection. Cases of hantavirus pulmonary syndrome--both new and retrospectively diagnosed--are still being recognized throughout the western United States. Many important questions remain unanswered.