The detection of a new virus called XMRV in the blood of patients with chronic fatigue syndrome (CFS) in 2009 raised hope that a long-sought cause of the disease, whose central characteristic is extreme tiredness that lasts for at least six months, had been finally found. But that hypothesis has dramatically fallen apart in recent months. Its public demise brings to mind an instance when a virus *was* successfully determined to be behind a mysterious scourge: the case of HIV and AIDS. How are these two diseases different—how was it that stringent lab tests and epidemiology ruled one of these viruses out, and one of them in?
The first inklings of the disease now called AIDS surfaced in Los Angeles in the summer of 1981. The 5 June 1981 issue of Morbidity and Mortality Weekly Report described 5 homosexual men with Pneumocystis carinii pneumonia (abbreviated PCP), normally only observed in individuals with weakened immune systems. The article suggested the possibility of an immune dysfunction related to exposure to something that would make individuals vulnerable to opportunistic infections. Soon clusters of PCP and Kaposi’s sarcoma, a rare skin cancer, were observed in gay men in other urban centers. The Centers for Disease Control and Prevention established a simple case definition—Kaposi’s sarcoma or opportunistic infections—and began scouring hospital records. Over time this definition was modified, but its early use identified an ongoing epidemic, and identified groups at risk for the disease as men who have sex with men and injection drug users.
The next year the new disease was called AIDS, and soon the U.S. Public Health Service recommended that members of risk groups not donate blood or plasma. Soon came reports that the disease could be acquired by newborn babies from their mothers, and also by heterosexual contact. By the fall there were nearly 700 people who had been diagnosed with AIDS in the U.S., of whom almost 300 had died. The CDC and World Health Organization worked together to publish global data on the disease, and issue recommendations to prevent its spread.