MRO Magazine

Plant Safety: Guard against an outbreak of airborne disease


June 1, 2005
By PEM Magazine

Almost 30 years ago, the American Legion held a convention at the Bellevue-Stratford Hotel in Philadelphia, PA, to celebrate the American bicentennial. Illness struck 221 persons within two days.

Seventy-two of which didn’t even attend the convention, but were in or near the hotel over the same period. Thirty-four people eventually died of the then mysterious and undetermined epidemic.

What followed was one of the largest investigations in U.S. medical history. During the fall of 1976, theories for what caused the illness outbreak ranged from chemical exposures to pneumonia to various conspiracies against American war veterans. The Centres for Disease Control (CDC) eventually shifted the focus of their investigation to the Bellevue-Stratford Hotel.

The CDC collected numerous samples from the water, soil, air and various materials from the hotel. All samples returned negative results. Finally, in mid-January 1977 it was determined by investigators that a bacterium was the cause of the newly named “Legionnaires" disease.


Upon further investigation, it was revealed that the bacteria thrived in the hotel’s cooling tower. From that water supply, the hotel derived its air conditioning. This is how the bacteria was actively dispersed into the hotel. The Legionnaires outbreak forever changed air-conditioning maintenance for years to come.

Today, more stringent cleaning and hygiene provisions for cooling towers and large-scale heating, ventilation and air conditioning (HVAC) systems are required. Since 1977 to present day, more than 40 different species potentially affecting HVAC systems have been identified.

Legionellosis is an uncommon infection caused by a bacterium called Legionella pneumophila. There are two types of illness, which can develop after being infected with this bacterium. Pontiac fever is a milder flu-like illness without the accompanying pneumonia.

Legionnaires’ disease is a type of pneumonia, which can occur in outbreaks. This condition varies in severity and is sometimes fatal. Legionnaires disease has historically been linked to HVAC systems, but in recent years, there has been scientific evidence to shift this view from only HVAC systems to potable water systems.

Legionellae bacteria are commonly present in natural and man-made aquatic environments, as well as soil and in ground water. They’re generally present, however, in very low concentrations. Under certain conditions within water systems, the concentrations may increase markedly.

ASHRAE lists the following conditions that are favourable for Legionella amplification: water temperatures of 77 degrees Fahrenheit (25 degrees Celsius) to 107.6 degrees Fahrenheit (42 degrees Celsius), stagnation, scale and sediment, biofilms and the presence of amoebae.

There’s also an indication that growth of Legionella is influenced by certain materials. Natural rubbers, wood and some plastics have been shown to support the amplification of Legionella. It has also been shown that materials, such as copper and silver, may actually inhibit the growth of Legionella.

Most of the data on transmission of Legionnaires disease suggests that it occurs most often in water, which contains the organism, is aerosolized in respirable droplets (less than five micrometers) and inhaled by a susceptible host. A variety of aerosol- producing devices have been associated with outbreaks that are common in large building and homes.

Examples include water distribution systems (i.e. showers and taps), whirlpool spas and hot tubs, humidifiers, cooling towers of large HVAC systems and respiratory therapy devices used in hospitals. Legionella has long-term survival, but exhibits no growth in sterile tap water.

Anyone can get Legionnaires disease, but the risk of developing the illness is greater for people who are middle-aged and older. It’s uncommon for people under the age of 20 to get the disease. Smokers, people with chronic lung or kidney disease, diabetes; weakened immune systems due to conditions (i.e. cancer or organ transplants) are also more at risk.

Legionella, isn’t a common disease and the risk of getting it is generally quite low. There’s no evidence of human-to-human transmission. Reducing the risk of Legionella in large buildings can prove problematic, as it’s difficult to predict where or when the bacterium is present.

Analysis and collection of Legionella is best done by swab samples over the medium where the water flows and sent to an accredited laboratory. Health Canada suggests the key to controlling the risk in large buildings is a combination of good engineering practices and infection-control policies and guidelines.

Doug Linman, B.Sc., CAIH, is an occupational hygienist with Golder Associates, Environmental Services Division in Edmonton. For more information call (780) 483-3499 or visit: