In 1866, the New York Legislature formed the New York City Metropolitan Board of Health.
Years before 1866, cholera arrived in New York City. A bacteria spread through water, cholera causes severe diarrhea and dehydration, which can cause death if not treated quickly. People noticed that the poorer areas, those less sanitary, produced the more infected people. At this time they did not have effective ways to deal with the dehydration, so this concerned people. They also worried about the spread of cholera.
To help with this problem the New York Legislature formed the New York City Metropolitan Board of Health. The board identified unsanitary conditions and issued orders to help clean it up. They also set up quarantine areas for people arriving on boats with cholera. Their quick and public response showed an example for other cities on how to respond to pandemics.