He established one of the earliest municipal public health laboratories in 1888, and the Providence City Hospital for contagious diseases in 1910.

[3] The Sources and Modes of Infection (1910) influenced physicians and public health officials across United States and Europe by demonstrating the central importance of the human carrier who does not have the symptoms of the disease but carries the germs and spreads it.

[6] Chapin's report also documents the speed at which laboratory services had become an important part of the public health system.

His parents were Joshua Bicknell Chapin, variously a physician, pharmacist, photographer, and the Commissioner of Public Schools for Rhode Island; and Jane Catherine Louise Value, an artist and art teacher who painted portraits and miniatures.

[5] Chapin also helped to establish the Providence City Hospital in 1910 to focus solely on the treatment of contagious diseases.

"[15] Chapin tracked the incidence of smallpox in the United States between 1895 and 1912, compiling a detailed outline that considered patterns of transmission and severity of variants of the disease.

[17] Cholera epidemics threatened Providence several times during the 1880s; Chapin's response was to make personal inspections of every home and tenement in the city to remedy problems.

[9] In The Sources and Modes of Infection (1910), Chapin had emphasized that "the effectiveness of isolation varies inversely as the number of missed cases and carriers".

He argued that the tactic of isolating people who were symptomatic for an illness would be unsuccessful if large numbers of undiagnosed or asymptomatic cases still remained in the overall population.

[9] Throughout October and November Chapin and others advocated for people to take precautions to avoid contagion, and to promote their general health through measures such as good nutrition, exercise, and sleep.

“Above all, leave alcohol alone and keep out of bar rooms.”[18] Chapin continued to promote precautions against influenza into December, while cases were declining, to avoid another wave of infection.

[18] The spread of the influenza reached its highest level in mid-October, dipped for a few weeks, then returned for a smaller second wave in January 1919.

[23] By 1910 his book Municipal Sanitation in the United States (1900) was the standard text on urban public health.

Later review found five of the papers particularly noteworthy, including The Fetich of Disinfection (1906), and Studies in Air and Contact Infection at the Providence City Hospital (1911).

His emphasis on contact at close range, for example through touching, exchange of bodily fluids, and large respiratory droplets, would shape the next 100 years of infectious disease control.

[24] In rejecting miasma theory,[1] Chapin largely ignored the public health implications of pollution in the air and water supply, and hazardous chemicals, where germs were not involved.

He was compared to his forerunners in the field, Frank, Edwin Chadwick, Simon, Lemuel Shattuck, William Thompson Sedgwick, and Hermann Biggs, as one of the greats of all time in public health.

[14] In 1935, he was given Brown University's Rosenberger Medal, awarded by the faculty for “specially notable or beneficial achievement.”[14][36] Chapin was posthumously inducted into the Rhode Island Heritage Hall of Fame in 1966.