In May 1983, amid the rapidly escalating AIDS crisis, a doctor at the National Institutes of Health (NIH) promoted a stunning theory about the newly encountered disease in the Journal of the American Medical Association (JAMA). Noting that the same issue of the journal contained an article documenting one of the first cases of the immunodeficiency disease’s appearance in an infant, the author sounded an alarm about “the possibility that routine close contact, as within a family househ...