What to know about the bacteria found in well water that left hundreds sick The common bacteria has strains that can cause serious gastrointestinal illness.

After more than 500 people became sick from well water used at a Tennessee resort, many with vomiting and diarrhea, health officials confirmed this week that the culprit was E.coli.

The food-borne bacteria is common and some strains are notorious for causing serious gastrointestinal illness. The same kind of bacteria, though possibly a different strain, was blamed in the romaine lettuce-related illnesses earlier this year.

Here is more about how some strains of E. coli can make people sick.

What is E. coli?

The name E. coli, short for Escherichia coli, refers to a large group of bacteria that has different forms. Most strains aren’t harmful and are a normal part of everyone’s body. However, some others can cause diseases, ranging from bladder infections to fatal multi-organ failure, according the Centers for Disease Control and Prevention.

How do people come in contact with E. coli?

E.coli are plentiful in the environment. They can come from both human and animal intestines and are often found in stool. Like other bacteria, they thrive in water. Heavy rain can create runoff over a land area, which can then wash the bacteria into nearby crops or drinking water supplies like creeks or ground wells. When people consume the affected food or water, they can become ill.

E.coli bacteria can be passed from person to person, often when a sick person with unclean hands works with food or drink that another person consumes. Pets can also be infected and spread the bacteria.

Public health systems regularly monitor public drinking water supplies for E.coli and other harmful bacteria, by measuring bacterial colonies called coliforms. But private water supplies or smaller sources may not be monitored or tested as often.

E.coli contamination has been a common source of food- and water-related illness outbreaks, according to the CDC. Anyone who drinks contaminated water can get sick, but those with weaker immune systems, like the elderly and children, can become fatally ill.

What are the signs or symptoms of E.Coli illness?

Depending on the type of E.coli, people may show a variety of symptoms, ranging from mild nausea to kidney failure. Anyone who has been drinking from a contaminated source can experience vomiting, diarrhea, stomach pains and mild fever.

Some may feel ill three to four days after eating or drinking from a contaminated source, but it’s not uncommon for a person to feel ill on day one or even day ten.

How is it treated?

Most people who become ill from E.coli will feel better in five to seven days, without any medications. Some may require medical treatment or antibiotics for the disease and its potential side effects, like severe dehydration.

Water treatment systems can disinfect water with antibiotics or boiling, but even those can be inadequate. Some strains of E.coli may have become resistant to the antibiotics.

Preventing future cases

There’s no foolproof way to filter E.coli out of water, so the best prevention is to avoid contaminated sources.

Health officials recommend following good hygiene practices when handling food and water, including washing hands and food preparation surfaces. If there are any concerns, consider using bottled water for drinking and washing foods. The risk of E.coli contamination in bottled water is incredibly, incredibly rare.

Petrina Craine, M.D. is an emergency medicine resident physician in Oakland, California, working in the ABC News Medical Unit.