The most deadly infectious disease was the pneumonic form of the plague, the so-called Black Death of 1347–1351, with a mortality rate of 100 percent. Today, the disease with the highest mortality (almost 100 percent) is rabies in humans when it prevents the victim from swallowing water. This disease is not to be confused with being bitten by a rabid animal. With immediate attention, the rabies virus can be prevented from invading the nervous system and the survival rate in this circumstance is 95 percent. AIDS (acquired immunodeficiency syndrome), first reported in 1981, is caused by HIV (the human immunodeficiency virus). In 1993, HIV infection was the most common cause of death among persons aged 25 to 44 years. In 1999 alone, 14,802 U.S. residents died from the AIDS/HIV infection, according to the National Center for Health Statistics. Although still a significant cause of death among persons aged 25 to 44, it is no longer the most common cause of death.