Patient Zero: Solving the Mysteries of Deadly Epidemics

This nonfiction book for young readers traces the history of eight deadly epidemics, showing how "disease detectives," known as epidemiologists, uncovered the causes and transmission pathways of some of humanity's most feared diseases. The book blends dramatized scenes with explanatory science, following each epidemic from its earliest victims through the investigations that revealed how it spread.

The book opens by comparing epidemiologists to police detectives: Both visit the scene, interview witnesses, and build a case. The author defines key terms, distinguishing between outbreaks, epidemics, and pandemics, and explains that every investigation begins with the first known patient, called the "index case" by epidemiologists and popularly known as "patient zero." The author also identifies the international agencies that coordinate responses, including the World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention (CDC).

The first chapter recounts the Great Plague of London in 1665. Goodwoman Phillips, a poor woman living outside London's walls, developed fever and body aches and died on Christmas Eve 1664. A neighbor discovered signs of bubonic plague: red rings and a swollen purple lump called a buboe. John Graunt, a cloth merchant, had spent years analyzing the city's weekly Bills of Mortality, printed death records from each parish. Graunt discovered that plague outbreaks were preceded by "sickly years" when deaths from all causes rose above normal. His prediction proved correct as plague deaths climbed to 7,000 per week by fall, ultimately killing 68,000 of London's 450,000 residents. The plague bacterium, Yersinia pestis, was not identified until 1894, when Swiss scientist Alexander Yersin isolated it during an epidemic in Hong Kong.

The second chapter examines the 1854 cholera outbreak in London's Soho district. Six-month-old Frances Lewis fell ill with severe diarrhea at 40 Broad Street. Her mother, Sarah Lewis, emptied soiled wash water into the household cesspool beside the front steps, then drew drinking water from the nearby Broad Street pump. Frances died after four days, and her death certificate recorded the cause as exhaustion from diarrhea rather than cholera. Dr. John Snow, who suspected cholera spread through contaminated water rather than foul air as the prevailing "miasma" theory held, went door to door asking residents about their water source. Nearly every victim used the Broad Street pump. Snow presented his findings to the parish council, which ordered the pump handle removed, and the epidemic stopped. The Reverend Henry Whitehead, a local minister who had joined Snow's investigation while initially skeptical of his theory, discovered Frances Lewis's death certificate and realized her illness preceded the general outbreak by two days. Engineers confirmed that the cesspool's decayed brickwork had allowed sewage to seep into the well. Snow's door-to-door method and his dot map of cases became foundational tools of epidemiology.

The third chapter follows the investigation of yellow fever in Cuba in 1900. The U.S. Army, occupying Cuba after the Spanish-American War, sent four doctors led by Major Walter Reed to find the cause of a disease killing more soldiers than combat. The team tested whether yellow fever spread through contaminated clothing, a specific bacterium, or mosquitoes, as Cuban doctor Carlos Finlay had long argued. Dr. James Carroll, a bacteriologist, volunteered to be bitten by a mosquito that had fed on a fever patient and developed yellow fever three days later. Dr. Jesse Lazear, another member of the Army team, then contracted the disease, possibly through deliberate self-experimentation, and died. Reed designed controlled experiments: volunteers who slept in clothing from fever patients remained healthy, while a volunteer exposed to infected mosquitoes fell ill. Reed's team also pioneered informed consent by requiring volunteers to sign forms acknowledging the risks.

The fourth chapter examines typhoid outbreaks in New York beginning in 1906. When the wealthy Warren family fell ill at their summer home, sanitary engineer George Soper discovered that every household where cook Mary Mallon, an Irish immigrant, had worked over the past decade experienced a typhoid outbreak. Soper suspected Mary was an asymptomatic carrier, someone who harbors disease without showing symptoms. After Mary refused to provide samples, Dr. Josephine Baker, one of New York's few female doctors, arrived with police to obtain them. Tests confirmed Mary harbored Salmonella typhi, the bacterium that causes typhoid, and she was quarantined on North Brother Island in the East River. Released after three years on the condition she never cook again, Mary returned to cooking under a false name. A 1915 hospital outbreak was traced to her, and she was sent back to the island, where she remained until her death in 1938. The author raises questions about whether Mary was victim or villain, noting her lack of social power and the fact that 50 other healthy carriers were never quarantined.

The fifth chapter covers the Spanish influenza pandemic of 1918–19. Private Albert Gitchell, an army cook at the overcrowded Camp Funston in Kansas, reported to the hospital with fever during the winter of 1917–18, becoming the pandemic's first recorded patient. As American soldiers shipped out to fight in World War I, they carried the virus to Europe. Wartime censorship prevented reporting; because neutral Spain's press covered its outbreak freely, the disease became known as "Spanish influenza." Dr. Wade Hampton Frost led the first organized epidemiological investigation of influenza. After appearing to vanish in summer, the virus returned in fall as a far deadlier strain, producing bleeding, fluid-filled lungs, and rapid death. Frost's team interviewed nearly 113,000 people across 10 cities, revealing that elevated pneumonia deaths had preceded the outbreak and that the disease disproportionately killed the very old and very young. The pandemic killed an estimated 50 to 100 million people and spurred the creation of international health organizations.

The sixth chapter describes the 1976 Ebola outbreak in Yambuku, a remote village in Zaire (now the Democratic Republic of Congo). Schoolteacher Mabalo Lokela arrived at a mission clinic run by Catholic nuns, believing he had malaria. He received an injection of chloroquine, an antimalarial drug, from one of the clinic's five syringes, which were sterilized each morning but only rinsed between patients. Mabalo briefly improved, then deteriorated, bleeding from his ears, nose, and eyes. He died after seven days. Family members washed his body for burial according to custom, and within days, 21 funeral attendees fell ill. Dr. Peter Piot, a 27-year-old researcher at a Belgian tropical medicine institute, examined blood samples and identified a virus never seen before. Traveling to Zaire with a WHO investigation team, Piot discovered that the virus spread through contact with infected blood during funeral rituals and through unsterilized syringes at the clinic. The outbreak killed 280 of 318 infected people, and the virus was named Ebola after a nearby river.

The seventh chapter covers the emergence of AIDS in the early 1980s. At the UCLA Medical Center, Dr. Michael Gottlieb, an assistant professor of immunology, examined a young gay man named Michael who had thrush, a fungal infection normally appearing only in people with compromised immune systems. Michael died, and two more young men with identical symptoms followed. Gottlieb and Dr. Wayne Shandera, an epidemic control officer, published an article about the first five cases in June 1981, prompting doctors nationwide to report similar cases. CDC epidemiologists determined the disease spread through sexual contact, shared needles, and blood transfusions. LGBTQ+ activists organized under the slogan "Silence = Death" to demand government action, which had been slow in part because the disease initially appeared among marginalized groups. In 1983, French scientists at the Pasteur Institute in Paris discovered the virus, later named HIV (human immunodeficiency virus). Journalist Randy Shilts's 1987 book And the Band Played On misinterpreted a CDC case label, "Patient O" (for "outside of California"), as "Patient Zero," coining a term that entered popular culture. Microbiologist Dr. Beatrice Hahn later traced HIV to a simian immunodeficiency virus in wild chimpanzees in Cameroon.

The final chapter follows the emergence of COVID-19 through the story of Dr. Li Wenliang, a 33-year-old ophthalmologist at Wuhan Central Hospital. On December 30, 2019, Li read an internal email describing patients with pneumonia of unknown origin linked to the Huanan Seafood Market. He warned his medical school friends on WeChat, a Chinese social media platform, but the message spread publicly, and on January 3, 2020, police forced him to sign a statement retracting his warning. On January 11, Chinese scientists identified the cause as a novel coronavirus and sequenced its genome. Li developed pneumonia and was hospitalized on January 12. The virus spread internationally, and on January 23, Wuhan was placed under lockdown. Li died on February 6. In early February, the WHO sent a delegation to study China's response, which combined traditional public health methods with modern technology including contact tracing, the process of identifying and notifying people who had been exposed to an infected person. On February 11, the WHO named the disease COVID-19. The chapter discusses how the virus spreads through respiratory droplets and superspreading events, in which one infected person transmits the disease to many others in an enclosed space, as well as the disproportionate impact on Indigenous communities.

The book concludes by arguing that pandemics will continue as humans encroach on wild ecosystems, and that disease detectives will remain essential to protecting public health.