More than 100 people have contracted legionnaires' disease in Quebec City since July, including eight who have died from related complications.

Here are seven things you should know about the bacterial infection:

Name was coined in 1976

"Legionnaires' disease" got its name from the unfortunate delegates who became infected during an outbreak at an American Legion of Pennsylvania convention. Thirty-four people died.

The bacteria responsible for the disease was isolated and named Legionella pneumophila in 1976.

It’s a type of pneumonia

Legionnaires' disease, a severe pneumonia, is one of two distinct illnesses associated with the Legionella genus.

Its milder counterpart, Pontiac fever, is a non-pneumonia flu-like illness that is less common. People affected by the fever usually don’t need treatment and are able to recover within a few days.

Legionnaires' disease, however, varies in its severity and can be fatal.

Linked to wet environments

Legionella bacteria are found in water sources, and can survive for several months in an aquatic environment – especially in warm water or when algae and organic matter are present.

The bacteria may also do well in household devices, particularly those that produce mist — shower heads and humidifiers, for instance.

Although maintenance of these riskier spots may be straightforward in a small home, things become more complicated than cleaning and disinfecting when it comes to large indoor environments.

"Minimizing your risk in large buildings, such as hotels and hospitals, is difficult because you cannot predict where or when the bacteria will be present," says Health Canada, adding that good engineering and infection control practices are crucial in these cases.

Outbreaks have been traced back to water distribution systems, respiratory therapy devices , whirlpool spas and hot tubs, humidifiers, and even the cooling towers of large air-conditioning systems.

Cannot be spread person to person

People may become ill if they inhale steam or mist containing the bacteria that causes legionnaires' disease, but they cannot pass an infection on to others. More recent research suggests that Legionella microbes may enter the lungs if someone chokes while eating or drinking, thereby allowing fluids and particles to enter the lungs instead of the stomach.

Although outbreaks happen, isolated cases are more common and the general risk of getting the disease is relatively low.

Usually begins with a headache

The Canadian Centre for Occupational Health and Safety notes that the first sign of legionnaires' disease is usually a headache accompanied by pain in the muscles and "a general feeling of unwellness." These symptoms may be followed by:

  • High fever (up to 40-40.5° C)
  • Shaking chills
  • Coughing
  • Fatigue
  • Loss of appetite
  • Nausea
  • Vomiting
  • Diarrhea
  • Dry coughing and chest pain (usually after two or three days)
  • Difficulty breathing
  • Confusion and disorientation
  • Hallucination
  • Memory loss

"The pneumonia might involve both lungs and become so severe that hospitalization is required," noted the centre, adding that pneumonia linked to legionnaires' disease is similar to pneumonia from other causes.

Special laboratory tests are usually needed to deliver a solid diagnosis of illness caused by Legionella bacteria.

Older, less healthy people at greater risk

Not everyone who is exposed to the bacteria develops legionnaires' disease. People under age 20, for instance, are much less vulnerable.

Middle-aged and older people are at greater risk, as are smokers. People who have diabetes, a weakened immune system and/or a chronic lung or kidney disease are also at increased risk when exposed to the bacteria.

Many kinds of workers may be exposed. The Canadian Centre for Occupational Health and Safety says the risk casts a wide net over a variety of indoor and outdoor occupations.

"The frequency of this disease occurring in workplaces cannot be evaluated or estimated because statistics are lacking," they write.

Health Canada singles out people who work on large air-conditioning systems or near other potential breeding grounds for the bacteria.

Usually not fatal

The majority of those infected survive, although their recovery can take several weeks. About five to 15 per cent of known cases have been fatal.

The odds of recovery depends on many variables, such as age and overall health, as well as the timeliness of medical treatment.

Those suffering symptoms of legionnaires' disease are advised to seek immediate medical attention, as most people are treated successfully with antibiotics.

If you suspect you have been exposed to the disease-causing bacteria, contact a physician or health professional.