Patient Zero

The episode begins with a live event announcement before diving into three interconnected narratives about finding the 'first cause' of major phenomena.

The first story concerns Mary Mallon, an Irish immigrant cook in early 1900s New York who became known as 'Typhoid Mary.' Sanitary engineer George Soper traced multiple typhoid outbreaks to her, discovering she was an asymptomatic carrier—infected with the typhoid bacterium but showing no symptoms herself. Despite having no symptoms, Mallon was contagious and spread the disease through food she prepared, particularly dishes with raw fruit like peach melba. When confronted, she violently rejected Soper's accusations. Health authorities forcibly isolated her on North Brother Island for three years. After a new health commissioner released her with a promise never to cook again, she secretly resumed cooking and caused another outbreak at a maternity hospital. She was returned to the island, where she spent the remaining 26 years of her life in isolation, even as hundreds of other healthy carriers (mostly men) were identified but not similarly quarantined, suggesting the response was more about public reassurance than epidemiological logic.

The second story traces HIV/AIDS back to its ultimate origin. While the disease became widely known in 1981 through cases in Los Angeles, the initial CDC study identified a central figure—Patient Zero, later revealed as Gaetan Dugas, a French-Canadian airline steward. Dugas became notorious as the supposed source of the American AIDS epidemic, accused of deliberately infecting others. However, genetic analysis of HIV revealed this was false. By examining the virus's mutations and diversity, scientists determined AIDS entered the US around 1966 when Dugas was still an adolescent. Tracing the virus further back to Haiti and then Africa, researchers identified two HIV-positive blood samples from Kinshasa (Democratic Republic of Congo) from 1959 and 1960. Using these samples and mutation rates as a 'molecular clock,' scientists calculated the virus originated around 1908. The source was traced to a specific group of chimpanzees in southeastern Cameroon, leading to the 'cut hunter hypothesis'—a Bantu man likely contracted HIV by butchering an infected chimp and getting infected blood in a cut. The virus then spread downriver to cities during the colonial period. The episode notes that HIV has actually spilled over into humans at least 12 different times from different animal species, but only one strain (HIV-1 group M) became the global pandemic affecting 60 million people.

The final story explores the origins of the high-five gesture. A press release claimed Lamont Sleets, a college basketball player at Murray State, invented the high-five based on his father's Vietnam military unit. When journalist John Moalem investigated, he discovered this was a fabricated story created as a collegiate prank to see if the media would run with it. However, Moalem had already researched the actual history and found Glenn Burke, a Black center fielder for the Los Angeles Dodgers, who initiated the gesture with teammate Dusty Baker during a 1977 playoff game after Baker hit a grand slam. The photo of this moment became iconic. Burke was the charismatic heart of the Dodgers clubhouse but was secretly gay. After management offered him $75,000 to get married (to a woman) and he refused, he was traded to Oakland. He faced harassment from coaches and fans, retired at 26, moved to San Francisco's Castro district, became addicted to crack, and died of AIDS in 1995, believing the high-five was his legacy. Yet even Glenn Burke may not be the true originator—women's volleyball coach Kathy Gregory documented high-fives among her players in the 1960s, and a 1955 French film shows the gesture. The episode concludes that with multiple potential originators, the 'best story' should be chosen, and Glenn Burke's remains the most compelling.