AIDS may be transmissible through casual contact - sharing utensils, toilet seats, doorknobs, or being in the same room as an infected person.

The first report appeared in the Centers for Disease Control's Morbidity and Mortality Weekly Report on June 5, 1981, five young men in Los Angeles, all previously healthy, all gay, all presenting with Pneumocystis carinii pneumonia and other opportunistic infections. The CDC noted the cases and invited clinicians nationwide to report similar findings. By year's end, 270 cases had been identified and 121 people had died. No one knew what caused the disease. No one knew how it spread.

In the absence of confirmed knowledge, the public filled the gap with fear. The disease, not yet named, referred to in early press coverage as 'gay cancer' or GRID, for gay-related immune deficiency, appeared to move through populations. If it moved through populations, it might move through ordinary contact. Newspaper coverage in 1981 and 1982 was often speculative about transmission. Public health officials, appropriately cautious given the incomplete data, hedged their early communications. In the void between what was known and what the public wanted to know, rumors flourished. The disease could be caught by sharing a glass, using a toilet seat, touching a door handle an infected person had touched, or simply being in the same room as someone who carried it.

Public health authorities moved to characterize transmission as evidence accumulated. In March 1983, the U.S. Public Health Service issued its first formal AIDS prevention recommendations, identifying transmission routes as paralleling hepatitis B, sexual contact and exposure to blood or blood products. By September 1983, the CDC had identified all major routes and explicitly stated that the disease was not spread through casual contact, food, water, or environmental surfaces. The epidemiological evidence was unambiguous. AIDS appeared only in people with identifiable exposures: gay men with multiple sexual partners, intravenous drug users sharing needles, hemophiliacs who had received contaminated blood products, infants born to infected mothers, and recipients of blood transfusions. Not in the households of patients. Not in the clinics where nurses cared for them without precautions beyond standard hygiene.

The biology behind this pattern would be characterized when the causative virus, human immunodeficiency virus, was identified in 1983 and 1984 by Robert Gallo's laboratory at the National Cancer Institute and Luc Montagnier's group at the Institut Pasteur. HIV targets CD4-positive T-lymphocytes and requires direct transfer of infected fluids at sufficient concentration to establish infection. The virus is fragile outside the body, rapidly inactivated by drying and exposure to air. The specific fluids capable of transmitting HIV, blood, semen, vaginal secretions, rectal fluids, breast milk, were documented. Saliva, sweat, tears, and respiratory droplets were not on the list.

The clarifications did not keep pace with the fear. By 1985, the epidemic had become a cultural crisis. Ryan White was a thirteen-year-old hemophiliac in Kokomo, Indiana, who had contracted HIV through a contaminated blood treatment. When the Kokomo school district learned of his diagnosis, officials moved to bar him from attending school. The official justification invoked the protection of other students, a risk that the CDC had definitively ruled out two years earlier. White's family fought the exclusion in court and won. He was permitted to return, to a reception that included shots fired at the family home and a bullet through their front door.

Other children were excluded from other schools. Adults with AIDS were fired from jobs, evicted from apartments, and refused treatment by doctors and dentists who feared infection despite federal guidance to the contrary. The discrimination was often framed in precautionary language: in the absence of certainty, some said, caution was reasonable. But certainty about casual contact had been established and published. It had been in the federal public health record since 1983.

By the early 1990s, accurate information about HIV transmission was standard in health education curricula. The science had been available, published, and clear. The challenge had never been what the science said. It had been whether the public and policymakers were prepared to act on it, and in the years when they were not, the people carrying the disease paid a cost the eventual correction of the record could not restore.