The first Legionella outbreak was in 1976. Today, Legionella is still rising in the United states.

Legionnaires’ Disease is rising in the United States


The first case of Legionnaires’ Disease broke out in Philadelphia, Pennsylvania, at the annual three-day convention hosted by the American legion at the Bellevue-Stratford Hotel in 1976. Over 2000 Legionnaires attended the convention and within a week more than 130 people had been hospitalized and 25 had died from the illness. The U.S. Centers for Disease Control and prevention (CDC) launched a large-scale investigation yet despite the significant efforts It took over a year before the bacterium that had caused the epidemic, Legionella pneumophilia, to finally be identified.

Before the 1976 Legionnaires Disease outbreak, Legionella pneumophilia was believed to only affect animals but was identified as the culprit when the bacterium was found in the cooling tower of the hotel’s air conditioning system. Legionnaires disease is contracted by respiration i.e. inhaling aerosolized water contaminated with the Legionella bacterium. In 1976, Legionella pneumophilia had cultivated in the hotel’s water cooler and then via the air conditioning system it had spread throughout the building.


Picture of Legionella bacteria

Image: Legionella bacteria

Since 1976 we have learned a lot more about the Legionella bacterium and how to prevent it from growing in our water systems. However, Legionnaires’ disease is often wrongly attributed a status as an exotic plague rather than what it really is – a relatively common form of severe pneumonia. In effect this has led Legionnaires’ disease to frequently be misdiagnosed as other diseases due to lacking clinical awareness. The Legionella pneumophilia bacterium are fastidious, not easily detected and are resistant to some types of municipal water treatment.  These facts combined make the the chances of Legionnaires’ Disease being accurately diagnosed and reported lower.

Incidence estimates vary, and it is hard to find reliable reports as many cases, if not most, are not detected. Even in instances when cases are detected the public rarely hears about Legionella outbreaks as they are settled quickly and under terms of confidentiality. The few times when outbreaks are reported to the public is in multi-case outbreaks such as the one in 1976. Yet, only a small percentage of cases are larger outbreaks helping to maintain the public perception that legionnaires disease is rare and not likely to affect persons. In reality, outbreaks are occurring all through the country every week.

Legionella bacterium is not hard to find but commonly resides in fresh water environments like lakes and streams and man-made water systems. Much thanks to Dr. Janet Stout, who in 1982 discovered the presence of Legionella in hospital water systems, it has since been understood that the larger issue is not cooling towers specifically, but Legionella prevention must focus on domestic (potable) water  systems holistically. Legionella is known to proliferate in many places such as plumbing systems, cooling towers, humidifiers, whirlpool spas and baths, respiratory care devices, ice machines, water fountains and more.

Prevention of disease and injury requires that each process in our water distribution systems such as conditioning, filtering, storing, heating, cooling, pressure regulation and distribution are all managed carefully with proper control measures. To stem the number of Legionella outbreaks in the country it is important that property owners, contractors and facility mangers are educated and understand the Legionella is not rare but congruent with our water distributions systems. Spearheading such efforts are states like New York which now require facilities to adopt and implement Water Management Plan that requires Legionella sampling of both their potable water and HVAC systems. Other states need to follow in these footsteps and make sure that no more people die from Legionella when the means to prevent these deaths exist yet are not being exercised.

The positive note is that in later years the CDC has developed a robust toolkit for the development and implementation of water management programs witch effective bacterial control and prevention based on the ANSI/ASHRAE Standard 188-2015, Legionellosis: Risk Management for Building Water Systems (ASHRAE 188) published in 2015. The 188 standard is the industry standard for effective and successful water management plans which includes control measures like physical controls, temperature management, disinfectant level control, visual inspections and environmental testing for waterborne pathogens and bacteria. The 188 standard supports water systems to control or eliminate harmful bacteria such as Legionella, Pseudomonas, Mycobacterium, Stenotrophomonas and others.

The 188 ASHRAE standard and the CDC toolkit is in no way being introduced too early as Legionnaires’ Disease is rising at an alarming rate in the United States.  During 2016 there was a 13.6 percent increase in cases reported compared to the 2015 when it increased only 7.8 percent. In other words, 2016 saw almost double the increase of cases compared to 2015. In fact, since the year 2000 the reported cases of Legionnaires’ Disease have grown by nearly four and a half times.

The increased number of cases reported may be the result of the improved standards and testing that have come particularly with the 188 standard and CDC’s toolkit.  The advent of water management plans may have changed the reporting and detection of Legionnaires’ Disease to become more accurate as well as it may have raised the clinical awareness allowing more cases to be properly diagnosed with the disease. There is of course also the possibility that there has been an increase of Legionella in the surrounding environment and in the susceptibility of the population, or some combination of these factors. Ultimately though, the increasing number of cases reflect what has already been previously stated, that Legionnaires Disease is a relatively common form of severe pneumonia and not a rare exotic plague.

Key Takeaways from the Article:

  • Legionella was first detected in 1977
  • For a long time Legionnaires’ Disease has been misdiagnosed and outbreaks failed to be reported
  • Legionnaires’ Disease is not an exotic but common form of severe pneumonia
  • To prevent Legionella, we have to focus on domestic potable water distributions systems
  • Since 2015 we have seen improved standards, regulation and reporting thanks to the ASHRAE 188 standard
  • Since 2000 the reported number of cases has grown by nearly four and a half times
  • More states need to follow the example of New York and adopt and implement greater water management standards
  • Means to prevent legionella bacterium from cultivating in our water systems exist but need to be exercised


As always, the goal of Aquamedix LLC is to help control the exposure of any bacteria that may reside and grow in domestic water. We want places that we visit such as medical centers, adult care facilities, schools, hotels, resorts, spas and health clubs to be protected and safe from Legionella and other waterborne pathogens. No matter whether it is an ice machine, water fountain or shower head, we want to ensure that you are protected and safe from any bacteria getting through to potentially harm or affect nearby persons or families. In short, we are committed to clean and safe water.


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