The final chapter relocates the setting to New York in 1858 amidst another yellow fever outbreak. Murphy stresses that little more is known about the disease than when it struck Philadelphia in 1793, and the consensus remains that it is imported. One difference is that a quarantine hospital is set up, but a mob who blames the Irish patients for bringing in the sickness burns it down.

Yellow fever continues to spread throughout several American cities during the 1800s, including Philadelphia. It also strikes other countries. France’s ambitions to expand their New World empire under Napoleon are foiled in the early 1800s, when tens of thousands of French soldiers fighting a Haitian slave revolt succumb to yellow fever. The fever also appears in South America, Europe, Russia, and West Africa. It emerges with warmer weather and large populations of people.

Throughout the 19th century, there are very few new developments regarding the disease. In 1848, Dr. Josiah Nott, a doctor in Alabama, observes that when the swamps are drained to kill mosquitoes, the fever seems to die off as well. Nott’s theory do not catch on until 1880, when Dr. Carlos Finlay decides to test it.