What is Legionnaires Disease?

Legionnaires’ disease is a form of a typical pneumonia caused by any type of Legionella bacteria. Over 90% of cases of Legionnaires’ disease are caused by the bacteria Legionella pneumophila. Other types include L. longbeachae, L feeleii, L micdadei, and L anisa.

There is a risk that the bacteria could flourish in the air conditioning systems of ships and buildings. The organisms breed in stagnant water or in wet deposits of slime or sludge. Possible locations for bacteria colonies are mentioned as being at the air inlet area and below the cooler (stagnant water), in the filter, in humidifiers of the water spray type and in damaged insulation.

Provision of adequate drainage is recommended to remove stagnant water.

Regular inspections and cleaning as necessary of filters and other parts, using a 50ppm super-chlorinated solution as the sterilizing agent is required. The solution is to be used also on the cooler drain area at not more than three month intervals. Regular sterilization is necessary for water spray type humidifiers (steam humidifiers being preferred).

The bacterium is found naturally in fresh water. It can contaminate hot water tanks, hot tubs, and cooling towers of large air conditioners. It is usually spread by breathing in mist that contains the bacteria. It can also occur when contaminated water is aspirated. It typically does not spread directly between people and most people who are exposed do not become infected. Risk factors for infection include older age, history of smoking, chronic lung disease, and poor immune function. It is recommended that those with severe pneumonia and those with pneumonia and a recent travel history be tested for the disease. Diagnosis is by a urinary antigen test and sputum culture.

There is no vaccine. Prevention depends on good maintenance of water systems.


The number of cases that occur globally is not known. It is estimated that Legionnaires’ disease is the cause of between two and nine percent of pneumonia cases that occur in the community. There are an estimated 8,000 to 18,000 cases a year in the United States that require hospitalization. Outbreaks of disease account for a minority of cases. While it can occur any time of the year it is more common in the summer and fall. .

Legionnaires’ disease acquired its name in July 1976, when an outbreak of pneumonia occurred among people attending a convention of the American Legion at the Bellevue-Stratford Hotel in Philadelphia. Of the 182 reported cases, mostly men, 29 died. On January 18, 1977, the causative agent was identified as a previously unknown strain of bacteria, subsequently, named Legionella, and the species that caused the outbreak was named Legionella pneumophila.

Outbreaks of Legionnaires’ disease receive significant media attention. However, this disease usually occurs in single, isolated cases not associated with any recognized outbreak. When outbreaks do occur, they are usually in the summer and early autumn, though cases may occur at any time of year. Most infections occur in those who are middle-aged or older. National surveillance systems and research studies were established early, and in recent years improved ascertainment and changes in clinical methods of diagnosis have contributed to an upsurge in reported cases in many countries. Environmental studies continue to identify novel sources of infection, leading to regular revisions of guidelines and regulations. About 8,000 to 18,000 cases of Legionnaires’ disease occur each year in the United States, according to the Bureau of Communicable Disease Control.

Between 1995 and 2005, over 32,000 cases of Legionnaires’ disease and more than 600 outbreaks were reported to the European Working Group for Legionella Infections. Data on Legionella are limited in developing countries and Legionella-related illnesses likely are underdiagnosed worldwide. Improvements in diagnosis and surveillance in developing countries would be expected to reveal far higher levels of morbidity and mortality than are currently recognised. Similarly, improved diagnosis of human illness related to Legionella species and serogroups other than Legionella pneumophila would improve knowledge about their incidence and spread.

A 2011 study successfully used modeling to predict the likely number of cases during Legionnaires’ outbreaks based on symptom onset dates from past outbreaks. In this way, the eventual likely size of an outbreak can be predicted, enabling efficient and effective use of public health resources in managing an outbreak.

The first recognized cases of Legionnaires’ disease occurred in 1976 in Philadelphia, Pennsylvania. Among more than 2000 attendees of an American Legion convention held at the Bellevue-Stratford Hotel, 182 attendees contracted the disease and 29 of them died.

In April 1985, 175 people in Stafford, England, were admitted to the District or Kingsmead Stafford Hospitals with chest infection or pneumonia. A total of 28 people died. Medical diagnosis showed that Legionnaires’ disease was responsible and the immediate epidemiological investigation traced the source of the infection to the air-conditioning cooling tower on the roof of Stafford District Hospital.

In March 1999, a large outbreak in the Netherlands occurred during the Westfriese Flora flower exhibition in Bovenkarspel; 318 people became ill and at least 32 people died. This was the second-deadliest outbreak since the 1976 outbreak and possibly the deadliest as several people were buried before Legionnaires’ disease had been diagnosed.

The world’s largest outbreak of Legionnaires’ disease happened in July 2001 with people appearing at the hospital on July 7, in Murcia, Spain. More than 800 suspected cases were recorded by the time the last case was treated on July 22; 636–696 of these cases were estimated and 449 confirmed (so, at least 16,000 people were exposed to the bacterium) and six died, a case-fatality rate around 1%.

In late September 2005, 127 residents of a nursing home in Canada became ill with L. pneumophila. Within a week, 21 of the residents had died. Culture results at first were negative, which is not unusual, as L. pneumophila is a fastidious bacterium, meaning it requires specific nutrients and/or living conditions in order to grow. The source of the outbreak was traced to the air-conditioning cooling towers on the nursing home’s roof. As of 12 November 2014, 302 people have been hospitalized following an outbreak of Legionella in Portugal and 7 related deaths have been reported. All cases, so far, have emerged in three civil parishes from the municipality of Vila Franca de Xira in the northern outskirts of Lisbon, Portugal and are being treated in hospitals of the Greater Lisbon area. The source is suspected to be located in the cooling towers of the fertilizer plant Fertibéria.

Twelve people were diagnosed with the disease in the Bronx, New York, in December 2014; the source was traced to contaminated cooling towers at a housing development. In July and August 2015, another, unrelated outbreak in the Bronx killed 12 people and made about 120 people sick; the cases arose from a cooling tower on top of a hotel. At the end of September another person died of the disease and 13 were sickened in yet another unrelated outbreak in the Bronx. The cooling towers from which the people were infected in the latter outbreak had been cleaned during the summer outbreak, raising concerns about how well the bacteria could be controlled.

On August 28, 2015, an outbreak of Legionnaire’s disease was detected at San Quentin State Prison in Northern California.

Between June 2015 and January 2016, 87 cases of Legionnaires’ disease were reported by the Michigan Department of Health and Human Services for the city of Flint, Michiganand surrounding areas. 10 of those cases were fatal.
Legionella is a naturally occurring bacterium and can be found in low concentrations in soil and water. In manmade structures and warm environments (35-46 degrees), the bacterium thrives and can multiply to levels dangerous to humans.

When the bacterium becomes airborne, carried in water particles, it can be inhaled into the lungs, causing Legionnaires’ disease, a highly virulent form of pneumonia. It has been found that while the bacteria will not grow in cold conditions, it can survive freezing. If the bacterium is present in the water system used by the ice machine, it can be encased in the ice and released as the ice thaws.

Just as a building’s water pipes placed too close to sources of heat can lead to Legionella growth, ice dispensers contain compressors that can also warm the machine’s incoming water lines, allowing Legionella bacteria to thrive if the systems are not properly tested and treated.

The use of chlorine is a common treatment to prevent Legionella growth in water systems. Charcoal filters used to remove chlorine from the cold water line to make it more palatable for drinking can, however, also leave that water susceptible to Legionella contamination.

People with compromised immune systems are particularly at risk of contracting Legionnaires’ disease, a severe form of pneumonia that can prove deadly given the patients’ already existing health problems.

Severely, ill patients are often offered ice to suck on to rehydrate and moisten their mouths, which leads to aspiration (the breathing in of the water particles), and infection where those water particles are contaminated with Legionella.
The risk of Legionella contamination in ice machines is well documented. South Australia had several cases of Legionella related to ice machines ten years ago and it has also been documented overseas.

While most hospitals and facilities have measures of testing and prevention in place, ice and water dispensers should be included in any risk assessment for Legionella in all health care facilities.

Australian publication titled “Guidelines for the Control of Legionella in the operation and maintenance of water distribution systems in health and aged care facilities” recommends all water systems in a health or aged care facility be assessed and controls put in place to minimise patients’ risk of exposure to this highly preventable, but often deadly disease.

Vulnerability of Water and Ice Dispensers

1) The ice dispenser’s compressor can heat the piping inside the machine and warm the cold water supplied. This supports Legionella growth.
2) The charcoal filter on the cold water line removes the chlorine in the water therefore removing any residual to disinfect.
3) The bacteria can multiply.
4) The water becomes ice with the bacteria present (alive but not multiplying).
5) Patients in hospital, suck on the ice, which leads to aspiration (breathing in of the water droplets). This is a very direct route & therefore, presents a very high risk for patients. When the patient’s immune system is suppressed the Legionella can quickly hide and mimic some of the remaining immune cells in the patient’s immune system to proliferate. Hence, the patient has very little ability to fight the infection.
6) Ice and water dispensers should be included in any risk assessment for Legionella in all health care facilities.
Vulnerability of Cruise Ship Industry

There has been a tremendous amount of bad press for the cruise ship industry recently. Ships have exposed passengers to danger by traveling through hurricane-level sea on the Royal Caribbean Anthem of the Seas, and on the Celebrity Infinity with outbreaks of norovirus.

Cruise ship hot tubs can create potential of an exposure to Legionnaires’ disease if not regularly drained and properly maintained. 

There can be no doubt that cruise ship companies make every attempt to provide pleasant cruises for its passenger-customers. Indeed, there are many great features and amenities to a cruise for the traveler. For example, here is a list of those features in a review of the Celebrity Silhouette. Regardless of the intent for customer comfort and safety, cruises as vacation destinations throughout the world are also a common setting for exposure to communicable diseases such as legionella, norovirus, and other serious illnesses.

With the entrance of the largest ship to the vacation cruising fleet, the Harmony of the Seas, we should consider the risks of the outbreaks of communicable diseases while aboard cruise ships.

Swimming Pools & Hot Tubs on Cruise Ships

A passenger on a certain cruise ship recently explained that he and his family are regulars on cruise ships, and they routinely take cruises more than once or twice a year. Unfortunately, there was an exposure to legionella on a most recent cruise. It appears that while most ships drain their pool and hot tub between ports, and commonly use salt water in the pools, this ship used a chlorine-based pool and did not drain and clean the pool between ports. While the CDC has outlined safety regulations for cruise ship swimming pools, if a cruise ship fails to drain the and test the pools during the voyage, it is certain to raise the potential of an exposure to legionnaires disease.

In fact, a 1994 Outbreak of Legionnaires Disease aboard the Celebrity Cruise Ship Horizon resulted in a multi-million dollar award in damages. The case was retried, resulting in a reduced award in the tens of millions of dollars. In the case, at least 16 persons who had sailed on nine separate week-long cruises were subsequently found to have Legionnaires’ disease, according to the U.S. Centers for Disease Control. One of the passengers later died. Essef Corp, provided a defective filter in the ship’s hot-tub system, which the CDC linked to the outbreak. The outbreak of Legionnaires ultimately resulted in a number of personal injury suits and a class action suit by passengers against Celebrity.

Center for Disease Controls Reports and Recommendations

A review of the Center for Disease Controls website includes a database of reports of norovirus and legionnaires cases per year.

The CDC specifically advises that:

More than 20%–25% of all Legionnaires’ disease reported to CDC is travel-associated. Clusters of Legionnaires’ disease associated with hotel or cruise ship travel are difficult to identify, because travelers often disperse from the source of infection before symptoms begin. In evaluating cruise travelers for Legionnaires’ disease, clinicians should do the following:

  • Obtain a thorough travel history of all destinations from 10 days before symptom onset (to assist in the identification of potential source of exposure)
    • Collect urine for antigen testing
    • Collect respiratory secretions for culture, which is essential for identifying the pathogen

Vulnerability of Hotel Industry

Bacteria causing a sometimes deadly type of pneumonia were found in the water system of the famed Las Vegas Rio All-Suite Hotel and Casino.

The Southern Nevada Health District announced two separate guests who stayed at the hotel at different times in March and April contracted Legionnaires’ disease, which is caused by the Legionella bacteria.

The US Centers for Disease Control and Prevention describes Legionnaires’ disease as a type of bacterial pneumonia, which causes coughing, shortness of breath, fever, muscle aches and headaches. Health officials said the disease can sometimes result in death.

The hotel and the health district are investigating the two cases, remediating the problem and reaching out to past and current guests.

After the two cases were reported, officials took a water sample, which showed Legionella existed throughout the facility’s water system.

People take in the bacteria by breathing in small contaminated droplets of water. Showers, faucets, hot tubs and fountains can carry the bacteria.

The Rio hotel, like other Las Vegas hotels, offers gambling buffets, shows and a pool. The magicians Penn & Teller perform there, so do the Chippendales dancers.

Heating, Ventilating, and Air Conditioning (HVAC) Systems

Legionnaires’ disease bacteria (LDB) cannot survive without water, and a properly operated, well-maintained HVAC system is unlikely to be a source of problems unless water contaminated with the bacteria enters the system. Air conditioning units without humidifiers have not been identified as sources of LDB. For a Legionnaires’ disease outbreak to be linked directly with the HVAC system, LDB-contaminated water must enter the system, be aerosolized, and be delivered to building occupants.


Operate and maintain all HVAC equipment as originally designed, and maintain it so that it can perform as designed. Test all HVAC equipment periodically to ensure that it is performing as designed. Consider the following issues while designing HVAC systems; most apply to all types of microbial contamination:

  • Minimize use of water reservoirs, sumps, and pans.
    • Provide a way to drain water sumps when not in use, such as, an electric solenoid valve on the sump drain.
    • Provide a bleed for water sumps so that dissolved solids do not form sediments in the sump.
    • Slope collection pans and drain sumps from the bottom so that all the water can drain out and allow the pan to dry.
    • Locate HVAC fresh-air intakes so that they do not draw the mist from a cooling tower, evaporative condenser, or fluid cooler into the system. When evaluating this path, consider:
    – Prevailing wind direction and velocity.
    – Building effects such as low-pressure zones on leeward sides of buildings and on roof.
    – Architectural screen walls.
    – Distance from tower to intake.
    • Design indirect evaporative cooling systems with the knowledge that the failure of the heat exchanger will allow wet systems to mix with the air-distribution systems.
    • Do not use raw steam from the central heating boiler to humidify air because it contains corrosion inhibitors and anti-scaling chemicals.
    • Atomizing humidifiers should have contaminant-free water.


Inspect the entire air distribution system (including return and exhaust systems) for visual evidence of water accumulation.

  • Properly drain all sumps and permanently drain inactive sumps to prevent accumulation of sediments.
    • If an HVAC sump is used during the hours when a building is occupied, drain the sump during unoccupied hours.
    • Maintenance failures can produce stagnant water that can become an ideal environment for LDB growth if sufficiently warm (such as heated by sunlight).

Control of Contamination

To effectively control contamination, be aware of the conditions that may promote growth and distribute LDB:
External sources may emit contaminated aerosolized water that is drawn into a system’s fresh-air intake. Consider the following:

  • Fresh-air intake airways, typically concrete plenums located at grade level, supplying fresh air to air handlers in the basement or lower levels of buildings can collect organic material (such as leaves and dirt).
    • Aerosols from spray irrigation.
    • Open windows.
    Internal sources may provide contaminated aerosolized water that is then disseminated by the air-distribution system. Consider the following:
    • HVAC system humidifiers are potential sources of aerosol exposure if contaminated with LDB.
    • Direct evaporative air coolers with sprays or misters used as humidifiers include sumps, which may stagnate when not in use.
    • Indirect evaporative air cooling systems using water coils may develop a leak that may inject cooling tower water directly into the supply air stream.
    • Air-to-air heat exchangers may develop leaks, which may allow the wet air stream to mix with supply air and cause problems if the wet air stream is contaminated with LDB
    • Wet evaporative coolers, slinger air coolers, and rotary air coolers with improperly operated and maintained systems that use warm, stagnant sump water may be potential sources of LDB.
    • Residential humidifiers, such as free-standing or portable units, often contain sumps that are frequently contaminated with LDB.
    • Computer room air conditioners may contain a humidifier sump filled with contaminated water.
    Improperly drained condenser pans may produce tepid conditions that can encourage microbial and fungal growth.
    Treatment of a Contaminated System
    In the event LDB is detected, follow these steps for treatment:
    • Eliminate all water leaks and remove any standing water found in the system to ensure future drainage.
    • Replace or eliminate any water-damaged insulation in the system.
    • Operate the HVAC system using 100 percent outside air for eight hours before returning the building to normal operation.

When the building is returned to normal operation, keep outside-air supply rates as high as possible for one month. At a minimum, the outdoor air requirements of ASHRAE Ventilation Standard 62-2001 should be met.

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