One of those cases was fatal.
The state's Department of Health and Department of Environmental Protection is looking into the situation in Hamilton Township.
Trenton Water Works customers are being told to take precautions against Legionella growth in their water systems.
"Yeah, it concerns me because I'm a member of the American Legion and it killed a bunch of legionnaires in Philadelphia 20-25 years ago. So yeah it concerns me," said resident Dave Martin.
It was actually 1976 when the first outbreak of Legionnaires' disease occurred in Philadelphia.
Now in New Jersey, state health officials and Hamilton Township are looking into why the bacteria has repeatedly popped up in the area year after year in customers serviced by Trenton Water Works.
"We don't have enough data right now to conclusively say that there is an issue with Trenton Water Works versus maybe some older homes or things like that," said Hamilton Township Mayor Jeff Martin on Monday. "So that's why we are really working with the state to dig down into this issue in more detail."
Township officials say in 20 home samples taken recently, more than half of the homes showed the presence of Legionella.
Legionnaires' disease is a lung infection caused by inhaling Legionella bacteria, often carried by tiny particles of water in the air.
Showering, saunas and power washing are considered higher-risk activities for contracting the disease.
Precautions include regularly flushing pipes, cleaning or replacing shower heads, faucet screens and water filters, and keeping hot water heaters set above 120 degrees.
"In most healthy people, this is not a concern. But if you are over the age of 50, a former or current smoker, or have other underlying health conditions that put you more at risk for developing Legionnaires' disease, that's when it becomes serious," said Hamilton Township Health Officer Chris Hellwig.
Officials say this has primarily impacted TWW customers, not those who have Aqua NJ.
A spokesperson for Trenton Water Works released the following statement Monday:
"TWW has been working with state and local health officials on this difficult issue since September 2020. TWW has a five-municipality service area with a well-engineered distribution system that serves 217,000 residents.
In Hamilton Township, where Legionnaires has become a complex challenge, TWW continues to test and flush water mains, increasing this activity in the impacted areas where Legionnaires cases have been identified, and we are sharing data with officials in the process. Also, TWW has invested millions in cleaning and lining water mains in Hamilton Township.
Our laboratory and operations team will continue to work with our partners to identify the cause and formulate a science and data-driven resolution."