PORTLAND, Ore. (AP) — An outbreak of Legionnaires’ disease at a North Portland apartment complex has killed one person and sickened three others, county health officials said.

Multnomah County health officials said Tuesday they told more than 100 residents of Rosemont Court on Dekum Street to leave after residents contracted pneumonia, The Oregonian/OregonLive reported.

The health department said experts linked the outbreak Monday to the apartment’s water system. County officials are working to clean the building’s plumbing system and remove any remaining traces of Legionella, the bacteria that causes the disease.

The health department is working with Northwest Housing Alternatives, which owns Rosemont Court, to find other places for residents to stay, according to a news release. Multnomah County spokeswoman Julie Sullivan-Springhetti said residents were staying in Portland-area hotels, per a contract with the county, while health officials investigate the outbreak source.

People can contract the disease when they breathe in very small droplets of water with the bacteria. Most exposed to it don’t get sick but some people can contract severe pneumonia. Symptoms include fever, fatigue, muscle aches and headache. More serious symptoms include cough and chest pain. The disease is not spread person to person.

As of Monday 20 residents had left the building and officials said more were leaving Tuesday.