Disease Spread Quickly in Tight Quarters
There had been few safety regulations or density requirements for multi-family tenement housing. The buildings were cheaply constructed, with little concern for fireproofing. Living spaces in these buildings were frighteningly overcrowded since the density (how many people could live in a certain amount of space) went unregulated.
Thousands of immigrants coming through Ellis Island to start a new life in America found affordable housing in these unsafe buildings, and landlords were happy to let them fit as many in a living space as possible, as long as they paid their rent. If a resident became exposed to diseases like smallpox or tuberculosis, it would rapidly spread throughout the building. If the water became contaminated, the whole building would become ill. When mold and mildew grew rampant, the building became flagrantly unsafe. Tenement conditions ensured the human toll ended up much worse than in other, more well-tended dwelling types.