The Basics about Legionellosis and HVAC Systems

If you’re involved in any aspect of a building’s HVAC system, then you need to know about the bacterium known as Legionella, and more specifically, the type Legionella pneumophila. It’s one of the hottest and most important topics in the industry right now, not only because its ill health effects have been prominent in recent years (see, for example, the 2003 New York Times article “Health Officials Baffled by Rising Number of Legionnaires’ Cases”) but because HVAC systems were long ago identified as major culprits in the spread of it.

L. pneumophila is responsible for causing Legionellosis, or Legionnaires’ disease, a specialized type of pneumonia that causes high fever, chills, aches, coughing, and other symptoms. It also causes a milder form of the disease known as Pontiac Fever. Although cases of these diseases have now been traced back as far as the 1960s, the bacterium itself was discovered and named only three decades ago, when 221 attendees of a 1976 American Legion convention in Philadelphia came down with a serious illness of unknown origin and pathology. 34 of them ended up dying, and the story rapidly spread and generated a brief national panic among a U.S. public that had been primed for such a reaction by, for example, recent and prominent government warnings about the distinct possibility of a devastating outbreak of some epidemic disease, and also by popular entertainments like The Andromeda Strain—both the 1969 novel by Michael Crichton and its 1971 movie adaptation—which told a story about a mystery plague that decimates a small town. (For a detailed recounting of these events, see the 2006 New York Times article, “In Philadelphia 30 Years Ago, an Eruption of Illness and Fear.”) The bacterium that caused the disease was identified in January of 1977, and both the disease and the bacterium were named after that initial outbreak at an American Legion convention.

The reason this is all so important to HVAC professionals is that two of the most common places to find Legionella are cooling towers and large central air-conditioning systems. The bacterium thrives in stagnant warm water (hence its prevalence in cooling towers) and causes disease when people inhale contaminated mist or vapor. This means you could hardly think of a better method of spreading Legionnaires’ disease and Pontiac Fever than central air-conditioning, especially in buildings like hotels and hospitals where people gather in large numbers and make heavy demands on the heating and cooling systems. It was, in fact, the hotel’s central air-conditioning system that was eventually identified as the source for spreading the disease in the 1976 outbreak. Outbreaks have been traced to other sources—shower heads, indoor fountains, hot tubs, and more—but air-conditioning and associated components are among the most common culprits. This means the people who have access to and control over these systems constitute one of the major lines of defense against the spread of Legionnaires’ disease and Pontiac Fever. Although both conditions are treatable by antibiotics, up to 3 in 10 people who contract Legionnaires’ disease can die from it. When you consider that according to figures provided by the CDC, up to 18,000 Americans are hospitalized with the disease each year, it’s obvious that the best course is preventative—as in, stopping the disease from ever happening—rather than responsive.

And how does one accomplish that from an HVAC perspective? This will be the subject of future posts at Just Venting, as will the fact that Europe presently appears to be outpacing the United States in its effective implementation of far-reaching guidelines for the prevention and treatment of Legionella . The European standard is called “Approved Code of Practice and Guidance  L8” or “ACOP L8. For now, suffice it to say that successful prevention is tied to all phases and aspects of an HVAC system’s life cycle, from design to installation to operation to maintenance.

Despite significant advances in awareness, technology, and techniques, L. pneumophila has continued to make itself known frequently in the years since 1976. The biggest outbreak of Legionnaires’ Disease occurred in 2001 in Spain, and many outbreaks occur each year in various countries, including the U.S., where at least a dozen have already been reported in 2008. Many cases are traced to origins other than air-conditioning, and many have a source that is never positively identified, but in all cases, in all buildings, a properly designed, installed, operated, and maintained HVAC system can help to reduce risk and protect the health of the occupants.


Legionella (CDC Website)

Legionnaires disease (Mayo Clinic article)

Legionella (Wikipedia article)

Legionella pneumophila (Wikipedia article)

Legionnaires’ Disease (long entry at The Medical Dictionary)

One comment

Leave a comment


Submit Comment

© Goodway Technologies, 2023. All rights reserved. Just Venting is powered by Backbone Media, Inc.