Update: hantavirus pulmonary syndrome--United States, 1999.

Hantavirus pulmonary syndrome (HPS) is a rodentborne viral disease characterized by severe pulmonary illness and a case-fatality ratio of 43%. Sin Nombre virus is the primary hantavirus that causes HPS in the United States, and the deer mouse (Peromyscus maniculatus) is its predominant carrier. CDC-sponsored studies of rodent populations since 1994 have yielded data that suggest an increased risk for infection for humans in some areas of the southwestern United States during the summer of 1999. This report describes increases in human cases during January-May 1999, current hantavirus prevalence in rodent populations, the need for renewed attention to reduce the risk for hantavirus exposure, and the importance of physician awareness and early detection in the treatment of HPS.