Fresh evidences point to the low-level of chlorine in the water source as the likely cause of Legionnaires' disease outbreak in Flint City, Michigan.

Scientists from universities in Colorado and Michigan have confirmed that the lack of corrosion control in the municipal water source of Flint in Genesee County caused lead to penetrate the city's water pipes, contaminating the water supply.

The untreated water sickened at least 87 people and killed 12, the third largest recorded outbreak of Legionnaires' disease nationwide.

Water Crisis

In April 2014, Flint City officials temporarily switched to a cheaper water source from the Lake Huron to the Flint River but reportedly did not put proper controls in the water treatment system.

After the switch, residents noticed the discolored and acrid-smelling tap water from their faucets. Soon after, local hospitals reported rising cases of Flint residents getting sick with Legionnaires' disease.

The following year, scientists have found that the water supply was contaminated with lead and other heavy metals, even as local authorities denied that lead was leeching into the water pipes.

Corrosive And Contaminated Water

"What we discovered was that when the Flint River water went into the system it released a lot of iron, and removed the disinfectant from the water," says Marc Edwards, an engineering professor at Virginia Tech, who led the study.

"And in combination, those two factors, the iron as a nutrient and the disinfectant disappearing, allowed legionella to thrive in buildings where it could not do so previously."

The scientists studied the chlorine levels of the tap water in Flint and nearby unaffected cities before and after the water crisis.

Experts believe that the lack of corrosion control in the Flint Water Treatment facility has altered the water chemistry so that more chlorine than usual was needed to keep legionella bacteria from flourishing.

During the winter, Edwards recreated the water crisis in his laboratory and discovered that corrosive water can indeed cause bacteria to flourish.

This is the first scientific study linking the untreated water supply to the Legionnaires' disease outbreak.

During the first wave of the outbreak in 2015, state officials have prevented the U.S. Centers for Disease Control and Prevention from coming to Flint to investigate the cause of the outbreak.

What Is Legionnaires' Disease?

Legionnaires' disease is a severe type of pneumonia caused by a bacterium Legionella pneumophila that grows in water.

"It's a pneumonia, but what's different about it is, we don't share it like we do the flu or common cold," says Michele Swanson of the University of Michigan, who has been studying Legionnaires' for 25 years.

Legionnaires' disease is not transmitted from person-to-person contact. Most people get the respiratory disease from inhaling the bacteria. Older adults, smokers, and people with weakened immune systems are considered susceptible and at a high risk for this severe lung inflammation.

The legionella bacterium also causes Pontiac fever, a milder illness with flu-like symptoms such as fever and chills.