It was a truism among 19th-century physicians that, in the words of German epidemiologist August Hirsch, “[t]he history of typhus … is the history of human misery.” Commonly associated at the time with the crowded and unsanitary conditions of jails, ships and hospitals, typhus attacked destitute populations mercilessly. The medical community and laypersons alike often blamed victims of the disease for their own suffering, believing that vicious, debauched, and unhygienic lifestyles begat typhus. An 1836 outbreak of typhus in Philadelphia led to important changes in how physicians understood the disease, with important lessons for epidemiology in the age of COVID-19.

During the 1800s in the United States doctors had relatively few chances to witness true epidemic typhus firsthand, and historical references to “typhus” could refer to any number of afflictions, further muddying the historical record of how pervasive the disease was. In particular, American physicians at the time believed that typhus and typhoid were the same affliction, differing only in severity of symptoms.

In reality, they are two very different illnesses. Typhus is a bacterial infection transmitted through infected body lice, while typhoid is a food-borne bacterial infection affecting the intestines. The similarity in their names was due to the fact that both diseases produced similar symptoms, including a high fever and a characteristic rash consisting of small red dots.

The first physician to definitively distinguish the two diseases, on the basis of firsthand pre- and postmortem observations, was American doctor William Wood Gerhard . Born in 1809 in Philadelphia, Gerhard was the studious eldest son of a hatter. Upon graduating from the University of Pennsylvania Medical School in 1830, Gerhard continued his medical education in Paris, where he learned clinical methods such as paying attention to both quantitative as well as qualitative sensory details when treating patients. Gerhard returned to Philadelphia in 1833 to serve as resident physician at the sick wards of the city’s almshouse, then known as the Philadelphia Hospital.

During the winter of 1835-6, a mysterious disease manifested among patients. A high fever and “dusky” expression characterized the illness, but significantly, no patients indicated intestinal problems, a common symptom of typhoid. Initially, the hospital physicians, including Gerhard, believed the disease to be bronchitis or a similar ailment. By March, it became clear that the disease, whatever it was, had become epidemic, as cases grew in number.

The new cases “attracted the greater attention from their occurring in groups of several from the same house, and almost all coming from a particular neighbourhood,” Gerhard wrote in an 1837 article in The American Journal of the Medical Sciences . Specifically, most cases originated in a neighborhood at the southern edge of the city, extending into northern Moyamensing, an area infamous at the time for poverty and vice. But it was the density of the neighborhood, and not its economic status, that Gerhard identified as the primary contributing factor to the disease’s violence there. In departing from the common wisdom of his era, Gerhard attributed the spread of disease to physical proximity rather than moral corruption, laying the groundwork for new approaches to epidemiology.

The epidemic did not relent in 1836 as summer came—an “unusually cool” one, Gerhard remembered in his article. Gerhard applied what he had learned during his education in Paris in the early 1830s to his work in the United States during the 1836 epidemic in Philadelphia. With the help of his colleagues, including fellow Paris-educated physician Caspar Wistar Pennock, Gerhard leaned on his education to identify the disease in question as typhus. He included in his article the case of Margaret Walters, a 24-year-old assistant nurse. On March 17, having felt ill for a few days, Walters, who worked in the women’s medical ward of Philadelphia Hospital, began displaying a worrisome array of symptoms, including fever and loss of appetite. Over the next week the condition of Walters’s bowels appeared to deteriorate rapidly, despite regular enemas and sponging of the skin.

When studying in Paris, Gerhard had examined the bodies of typhoid patients, both before and after death. The intestines of typhoid patients often had inflamed or ulcerated nodules known as glands of Peyer or Peyer’s patches, named after a 17th-century Swiss anatomist. Given Walters’s symptoms, Gerhard had expected upon her death to see that her glands of Peyer were inflamed, but this was not the case; her intestinal tract was remarkably healthy. On the basis of these and similar observations, Gerhard concluded that typhus and typhoid were distinct diseases, affecting completely different parts of the body. While typhoid generated “morbid changes” of the intestines, typhus had no such effect, instead appearing to produce cognitive disturbance and muscular pains.

Gerhard estimated that the typhus epidemic affected around 250 of the Philadelphia Hospital’s patients between March and August of 1836. This number did not include those who fell ill at other institutions, or in the city at large. Most of the patients Gerhard observed were black, and Gerhard described the epidemic’s victims as primarily poor and “intemperate.” He calculated that roughly one in four of the typhus patients at the Hospital died. Black men, he noticed, seemed particularly susceptible. Gerhard attributed their vulnerability to the kinds of manual labor they typically performed, as well as their alleged drinking habits.

Initially, Gerhard and his colleagues dismissed the idea that typhus was contagious. At the time, most physicians believed few diseases were contagious; the exceptions—most notably smallpox—were those diseases observably transmissible through direct skin-to-skin contact. More often, physicians attributed diseases to “infection,” a loosely defined source of a variety of illnesses often arising from imported cargo, rather than from person-to-person transmission. As Gerhard’s familiarity with typhus increased, however, he grew to firmly believe in the disease’s contagion, emphasizing the contaminating nature of sweat; physicians did not yet know that typhus spreads through infected body louse feces. As evidence of the disease’s contagious nature from body to body, Gerhard recalled the case of a male nurse who, while shaving a dying patient, inhaled the patient’s breath. The nurse described the patient’s breath as having “a nauseous taste,” and almost immediately fell ill. Similarly, an “assistant was supporting another patient who died soon afterwards, he felt the pungent sweat [of the patient] upon his skin, and [the assistant] was taken immediately with the symptoms of typhus.”

It was clear that proximity to typhus patients put one at risk of contracting the disease. Based on his observations Gerhard concluded that, while the majority of cases were due to some unspecified environmental factor that caused the epidemic in the first place, many patients had caught the disease from someone else.

In 1836, medicine was an evolving science, just as it is now, and understandings of the human body were in flux. The dynamic quality of ideas about the body left plenty of room for an inquisitive mind like Gerhard to revise how physicians interpreted various symptoms and “morbid changes.” Doing so meant having enough pre- and postmortem evidence to back up his claims, which required some patients to die. While, for better or worse, Gerhard took the credit for discovering what made typhus and typhoid distinct, it was the bodies of his nurses and patients who provided the necessary proof for his conclusions.

Physical and sensory observations exposed Gerhard and other attending caregivers to typhus’s “matter of contagion” in ways that could prove deadly. Gerhard and his colleagues did not know that typhus spreads through body lice, but they recognized anecdotally that proximity to patients put them at risk of contracting the disease. Healthcare workers during the COVID-19 pandemic find themselves similarly exposed to potentially deadly pathogens. Recognizing the virulence of the coronavirus responsible for COVID-19, public health specialists quickly began advocating “social distancing” in an effort to curtail the spread of the virus. When practiced correctly and sensitively, social (or “physical”) distancing can limit the spread of pathogens and reduce the number of people falling ill at the same time, thereby allowing healthcare workers to better care for patients who do contract the disease.

“Social distancing” as a phrase did not exist in Gerhard’s time, but the concept was well-established. For centuries, leper colonies and lazarettos had sequestered bodies and cargos suspected of carrying disease. However, 19th-century medical beliefs about contagion inclined physicians to ignore restrictions on physical closeness when providing care. Gerhard’s somewhat more expansive definition of contagion, which included transmission through bodily fluids like sweat, alerted him to the potential dangers of being in close proximity with someone suffering from typhus. Even so, he did not prompt his colleagues to maintain what he understood to be a safe distance from typhus patients. Carefully practicing social distancing might have prevented Gerhard and his colleagues from making the kinds of observations that helped them understand the differences between typhus and typhoid, but it also might have saved the lives of nurses like Margaret Walters.

Such situations might sound familiar in 2020, when shortages of personal protective equipment for healthcare workers put many on the front lines at an unnecessary risk of contracting COVID-19. In 1836, typhus spread rapidly through crowded neighborhoods of Philadelphia, primarily affecting poor people who would have had few opportunities to socially distance themselves from their neighbors, families, and roommates. Many in the United States, not to mention elsewhere, face the same set of problems in 2020. Flattening the curve was scarcely a viable option in 1836, but it is imperative in 2020, in order to protect the health and wellbeing of frontline healthcare workers, as well as those unable to practice social distancing because of the work they perform or the conditions in which they live.