NTHONY

UMANKIND has been besieged through-out its evolution by microorganisms that pose a continual challenge to the surviv-al of the species. 1 Although such ancient killers as tuberculosis and malaria persistently take a toll of millions of lives per year, occasionally the emergence or reemergence of a microbe results in an unexpected, catastrophic pandemic with global pub-lic health consequences. As we prepare to leave the 20th century, it is worth reflecting on the fact that within the framework of an enormous but constant burden of a variety of infectious diseases, as well as a number of mini-epidemics, this century has wit-nessed two such unexpected cataclysmic events. One, the influenza A pandemic of 1918, was due to an old, but reemerging microbe. Influenza had been a problem for centuries, but in that one winter of 1918–1919, it was responsible for the deaths of ap-proximately 25 million people worldwide and 550,000 people in the United States. 2 The other pandemic, the acquired immunodeficien-cy syndrome (AIDS), is due to a newly recognized microbe, the human immunodeficiency virus (HIV). 3 The world first became aware of this new disease in the summer of 1981, and it has exploded in successive waves in various regions of the world. Still, as we en-ter the 21st century, the catastrophic potential of the pandemic may still not have been fully realized. As we prepare to enter the new millennium, it is appropriate to reflect on the origins of this epidemic, what has oc-curred over the past 18 years, what has been accom-plished from a scientific and public health perspective, and what the prospects are for the future.