Outbreak of hantavirus infection in the four corners region of the United States in the wake of the 1997-1998 El Nino-southern oscillation

Hantavirus cardiopulmonary syndrome (HCPS), a rodent-borne zoonosis, has be en endemic in the Americas for at least several decades, It is hypothesized that the 1991-1992 El Nino-southern oscillation (ENSO) caused increased pr ecipitation that allowed an increase in rodent population densities, thereb y increasing the possibility of transmission to humans. The result was a 19 93-1994 outbreak of the disease in the Four Corners states of the southwest ern United States. A second strong ENSO occurred in 1997-1998, after a peri od of considerable public education about the risks of hantavirus infection that began during the 1993-1994 outbreak. The caseload of HCPS increased 5 -fold above baseline in the Four Corners states in 1998-1999. Regions that had received increased rainfall in 1998 were especially affected. A large m ajority of the 1998-1999 case patients reported indoor exposure to deer mic e. Hantavirus outbreaks can occur in response to abiotic events, even in th e face of extensive public education and awareness.