Emerging infectious diseases: a challenge to all.

Emerging infections are defined as diseases of infectious origin with an incidence that has increased within the past two decades or threatens to increase in the near future. Some of these diseases are associated with newly discovered infectious agents; others are well-known conditions rapidly increasing in incidence. Five emerging infections are reviewed in this article: ehrlichiosis, a tick-borne infection caused by obligate intraleukocytic bacteria; infections caused by vancomycin-resistant enterococci, which have become a serious nosocomial problem; hantavirus pulmonary syndrome, a Sin Nombre virus infection associated with the adult respiratory distress syndrome and a high case fatality rate; infection with Escherichia coli strain O157:H7, which typically produces hemorrhagic colitis that may lead to the hemolyticuremic syndrome, and streptococcal toxic shock syndrome, a devastating illness often associated with necrotizing fasciitis and multiple organ failure.