The Saga of Legionella - Legionella

The Saga of Legionella

Author: Richard W Gilpin PhD.
Biosafety Officer, Johns Hopkins Institutions.
Adjunct Assistant Professor of Environmental Health Sciences, Johns Hopkins University School of Hygiene and Public Health.
Baltimore, MD.
Portions published in The Analyst, Summer 1995.

Legionnaires’ Disease rates have not changed since the disease was discovered. Last year, 1,222 people with Legionnaires’ Disease were reported to the CDC national passive surveillance program. It is known that the number of people who get Legionnaires’ Disease each year is actually much greater. The estimated number ranges from 10,000 to 50,000 Legionella pneumonia cases per year. Most hospitals do not report cases because the reporting is optional and also because diagnosis is difficult. Legionnaires’ Disease is not confined to the United States. By 1983, this pneumonia had been identified on six continents around the world. Often, without laboratory confirmation of diagnosis, people with signs and symptoms are treated with an antibiotic (intravenous erythromycin or oral rifampin) known to be effective against Legionella, the bacterium that causes Legionnaires’ Disease. Additional source information about Legionella is referenced (21, 33, 37).

The Origins of Legionnaires’ Disease.

In 1947, an individual contracted a pneumonia of unknown origin (presumed to be a rickettsia-like agent). In 1978, by culturing Legionella from frozen guinea pig tissue that had been injected with the patient’s blood, this pneumonia was found to be Legionnaires’ Disease (24). The second documented Legionella-caused pneumonia occurred in 1959 (24). Legionnaires’ Disease is not a new infectious disease; it has been around for quite some time. It has been hypothesized by some researchers that the increased number of people getting the disease is directly correlated with the increased use of water-containing mechanical equipment for building central air conditioning systems. In 1965 at a hospital in Washington, D.C., the first known cluster of many deaths by pneumonia of unknown origin, subsequently found to be Legionnaires’ Disease, occurred. Frozen samples of patient tissue confirmed this (11).

Legionella was directly correlated with illness and deaths at the Legionnaires’ Convention and the Odd Fellows Convention in Philadelphia during the summer of 1976. Lung tissue specimens from the people who were hospitalized with pneumonia after attending those conventions tested positive when the tissue was tested with a direct fluorescent antibody (DFA) test reagent made by immunizing rabbits with killed Legionella bacteria. Legionella were also cultured from these patient specimens in guinea pigs and on a newly developed culture medium.

Patient sera were also found to contain antibody produced in response to infection by the bacteria.

Before the discovery of Legionnaires’ Disease, people were hospitalized and died of a pneumonia that was not diagnosed or appropriately treated. It took the series of events in Philadelphia that led up to the discovery of a previously unknown bacterium to explain these prior mysterious pneumonia deaths.

Legionnaires’ Disease can be caused by Legionella growing in water-containing mechanical equipment which aerosolizes water.

In the early 1990’s press began to report on building related illness; often called sick building syndrome (14). One component of biological contamination contributing to workplace illness is Legionnaires’ Disease. In response to increasing public pressure to do something about sick building syndrome, and in response to recent cases of Legionnaires’

Disease associated with federal government buildings, the United States Occupational Safety and Health Administration (OSHA) recently requested comments and information from safety and facilities professionals so that consideration could be given to a proposed indoor air quality standard to deal with chemical, environmental and biological pollution in the workplace. Also, the United States Environmental Protection Agency (EPA) recently issued a guideline on building air quality for building owners and facility managers (60).

This disease is documented to be directly associated with people inhaling Legionella-contaminated air near the water-containing mechanical equipment (2, 5, 7, 8, 10, 11,15, 18-20,25, 28-30, 32,38). Legionella normally grow in biofilms near warm water and a humid atmosphere, especially in warm water- containing mechanical equipment. It is possible for Legionella to become trapped in micro-droplets (aerosols) of water if this equipment generates such aerosols. Contaminated aerosols may spread Legionella into the air where people inhale the bacteria into their lungs and contract Legionnaires’ Disease.

The first documented connection between cooling towers and Legionnaires’ Disease was a July 1978 outbreak among golfers at an Atlanta, GA golf course (7). The only major outbreak of Legionnaires’ Disease not associated with towers was the Wadsworth Medical Center outbreak of 1977-1978 (18). Reports have documented Legionella airborne transmission as far as 3,000 feet from a Legionella-contaminated cooling tower to nearby residents who acquired Legionnaires’ Disease (1, 2). Therefore, Legionella can be inhaled by people who are not at the immediate site of aerosol- generating mechanical equipment.

Legionella bacteria grow in lung tissue and cause death.

Two infectious diseases are caused by Legionella bacteria: Legionnaires’ Disease (sometimes called legionellosis) and Pontiac Fever. Legionnaires’ Disease is life-threatening and presents a much different clinical picture than Pontiac Fever, which is self limiting and rarely reported to physicians. During a Pontiac Fever outbreak, associated with a cooling tower containing 300,000 Legionella per milliliter, 83% of office workers and 68% of visitors were affected (11, 15). During a Legionnaires’ Disease outbreak, only 5% of the exposed population may get the disease. The mortality associated with Legionnaires’ Disease remains high. About 15% to 40% of patients with Legionnaires’ Disease die of pneumonia or of complications related to pneumonia. Most hospitals are not equipped to perform laboratory diagnosis of Legionnaires’ Disease during its early, critical stages, and as a result patients may not receive timely treatment (26).

Legionella bacteria cause a significant number of the pneumonias that people get. About 4% of all people that have pneumonia with an unusual lung x-ray have Legionella growing in their lungs (26). Pneumonia caused by Legionella is as common as pneumococcal (streptococcal) pneumonia and mycoplasma pneumonia in hospital admittees younger than age 70 (27).

The environmental source of Legionella bacteria.

The following is quoted from the EPA Health Advisory: (28) “Legionella are widespread in lakes and rivers. There is some indication that these organisms may be either very sparse or absent in groundwater. The possibility that humans may be exposed transiently to Legionella because of their intimate relationship with water is highly probable, given the high frequency of seropositivity to Legionella in healthy populations and the widespread occurrence of Legionella in water environments.

“In a number of outbreaks that have occurred in the United States, aerosols of water (documented to contain the specific type of Legionella that was recovered from the patient) have been identified as the vehicle for transmission.” (Also, there is strong, published evidence for involvement of aerosols from showers, spas, cooling towers, evaporative condensers and other heat rejection equipment.) “It has been hypothesized that Legionella enter buildings in very low numbers via the treated drinking water. These bacteria may proliferate in warm water when specific factors not determined fully allow them. Even when this occurs, as has been shown in numerous buildings, disease usually does not result. Cases and outbreaks of Legionnaires’ Disease occur only when aerosols containing Legionella possessing specific virulence factors (as yet not determined) are inhaled (possibly ingested) by susceptible individuals. Foodborne outbreaks or secondary spread have not been reported.”

How Legionella bacteria enter buildings and equipment.

Another quote from the EPA Health Advisory states: (40) “Legionella are found in raw water, in treated waters, and in plumbing systems, but the occurrence and fate of these organisms in the distribution system between these points are unknown. The organism may survive the treatment and disinfection process and pass intact through the distribution system. In addition, opportunities exist for their introduction into the system by means of broken or corroded piping, repair of existing mains, installation of new mains, back siphonage, and cross connections, any of which may result in contamination of the water supply. In older distribution systems, especially those dependent on gravity flow, deterioration of piping may be so severe that the treated water comes in intimate contact with soil and is subject to infiltration by surface water. Thus Legionella may be introduced into potable water by these routes. Legionella surviving initial water treatment may colonize pipe joints and corroded areas or adhere to the surface of sediment of storage tanks, especially those constructed of wood. Here, they may find a habitat suitable for survival and regrowth. Cul-de-sacs, intermittently used storage tanks and other sites in which water flow is absent or restricted also may be appropriate habitats for Legionella.”

Also, “there are numerous reports of the Legionella occurring in plumbing systems, especially in hot water systems. Most of these investigations have been carried out in hospitals, and many were prompted by outbreaks of hospital-acquired Legionnaires’ Disease. The primary reservoir in hospitals is apparently hot water tanks in which water is maintained at temperatures below 55°C (130°F). Legionella also have been found in shower heads, rubber fittings, aerator screens, faucet spouts and other plumbing fixtures.”

In addition, “only a few studies have been published on the effectiveness of various types of treatment for eradicating or reducing Legionella numbers at the water treatment utility. In one study, Tison and Seidler examined raw water and three kinds of distribution water supplies: (1) those treated by chlorine (free residual 0.2-6 PPM); (2) those treated by sand filtration and chlorination (free residual 0.0-4 PPM); and (3) those treated by flocculation, mixed media filtration and chlorination (free residual 0.5-2 PPM). Legionella were enumerated by direct fluorescent antibody (DFA) tests and all distribution waters contained about one order of magnitude fewer Legionella-like cells than did the raw waters, i.e., 1,000-10,000 per liter.”

Are maintenance workers at risk.

An investigation of cooling tower maintenance employees who worked around routinely maintained cooling towers gave inconclusive results. Maintenance employees were screened by questionnaire and by an indirect fluorescent antibody test of their serum for antibody to Legionella in order to check for current or past exposure to Legionella (8). It was found that 26% of the employee questionnaires suggested possible illness compatible with Legionella and 12% of the employees had significant antibody titers to Legionella. Questionnaire results indicated a statistically significant relationship between exposure to cooling tower Mist and possible Legionnaires’ Disease. However, serology results did not correlate with work exposure or reported illness.8 The end point titer criteria used during the investigation may have been set too high and therefore many seropositive workers were not counted. This may explain the lack of consistency between the questionnaire results and the serology results.

Building owners have been sued by Legionnaires’ Disease victims.

Legal liability has become a consideration among building owners who operate water-containing mechanical equipment. Victims, and their attorneys, began to realize that they had legal recourse against building owners if they contracted Legionnaires’ Disease at their workplace, at a hospital they visited for elective surgery or at other facilities they visited. Because some buildings were found to have water containing mechanical equipment fouled with Legionella, and the equipment was not appropriately disinfected and cleaned, or because people were not warned of the potential biological hazard, juries have awarded large monetary damages to Legionnaires’ Disease victims who got Legionnaires’ Disease (12).

Pre-Legionella preventive maintenance programs.

Until 1976, building HVAC and plumbing engineers were not very concerned with biological contamination as a source of sick building syndrome. Microbial contamination was usually controlled to increase equipment efficiency by routine maintenance procedures, including treatment with slime inhibitors and biocides (chemicals that kill or inhibit the growth of microorganisms). Before the Philadelphia outbreak of Legionnaires’ Disease, water in condenser pans and other HVAC equipment such as terminal reheat units, recirculating water heating and cooling units, air handling units, humidification systems, cooling towers and evaporative condensers was either kept to a minimum or it was treated with biocides to reduce microbiological fouling by fungi, algae, sulphate bacteria, iron bacteria or other microorganisms.

Standard preventive maintenance programs are not enough to stop Legionella from multiplying in water containing mechanical equipment.

The 1976 Philadelphia outbreak of a mysterious pneumonia with many deaths and the subsequent discovery, in 1977, of a previously unknown bacterium, Legionella,23 soon changed the preventive maintenance approach to microbial contamination of water-containing mechanical equipment. Water-containing mechanical equipment was later found to be the source of the Legionella which caused the mysterious pneumonia.

My microbiological field research with cooling towers and evaporative condensers led to the observation that numbers or Legionella are often highest on cooling tower vertical baffles (decking) that are intermittently covered with water. Numbers of Legionella within the sludge at the bottom of cooling tower sumps are often fewer in number. Also, counts of total numbers of heterotrophic, non-Legionella bacteria in cooling tower water have no relationship to the numbers of Legionella in the water (31). Therefore, checking total numbers of bacteria in cooling towers or hot water systems with common laboratory culture media will not predict the actual numbers of Legionella in this water-containing equipment.

Clearly, standard preventive maintenance procedures do not prevent water-containing mechanical equipment from becoming colonized with enough Legionella to create a health hazard (2, 5, 8, 10, 15, 19, 20, 22, 25, 28-32, 38, 39 41).

Will routine biocide treatments remove Legionella from water-containing mechanical equipment?

The answer is no (13, 30). However, building owners can manage potential Legionella problems by having their buildings’ water samples checked for numbers of Legionella on a routine basis. Most building owners are looking for a chemical or quick fix to the situation of Legionella contamination of water-containing mechanical equipment; none exists at this time. Some water treatment suppliers have suggested that simply removing algae from cooling towers will prevent Legionella growth. There are chemicals that successfully remove algae, but there are no known practical levels of chemical treatment for algae or bacteria that will keep Legionella out of cooling towers or domestic water systems (30). Using organic acids (which cause foaming) to remove scale in warm water-containing mechanical equipment may cause Legionella to concentrate in that foam and produce higher numbers in cooling tower water. Keeping tower water at elevated pH and alkalinity may help to keep Legionella numbers lower (42).

Several available biocides work well in laboratory simulations, but they do not seem to be as effective when used in operating equipment in the field. For example, a documented Legionnaires’ Disease outbreak was associated with an industrial cooling tower treated with appropriate levels of what was considered to be an effective anti-Legionella biocide, according to the recommendations issued by the Scottish Home and Health Department, Scotland. Samples examined bacteriologically just before the outbreak were negative, but at the time of the outbreak extensive and heavy Legionella contamination was discovered in cooling tower water, sludge, pipes and rubber grommets (38).

What should building owners be doing to reduce their liability?

Some building owners have been doing something about their legal liability. Several researchers in the environmental microbiology field recommend that warm water-containing systems that produce water aerosols be checked routinely to determine whether routine maintenance procedures are keeping down the numbers of Legionella.

The United States Environmental Protection Agency (EPA) indoor air quality guidelines state: (60) “Maintenance of a cooling tower ensures proper operation and keeps the cooling tower from becoming a niche for breeding pathogenic bacteria, such as Legionella organisms. Cooling tower water quality must be properly monitored and chemical treatments used as necessary to minimize conditions that could support the growth of significant amounts of pathogens.”

When the equipment becomes a public health concern, the equipment needs to be disinfected with appropriate concentrations of biocide and cleaned in order to reduce the numbers of Legionella being spread into the air (10, 30).

I recommend that water-containing equipment be routinely monitored by a qualified Legionella testing environmental laboratory and when found to contain elevated numbers of Legionella, disinfected with biocidal chemicals, such as swimming pool chlorine, when necessary. Other scientists recommend disinfection of sites such as cooling towers shown to contain significant numbers of Legionella (10). However, routine continuous chlorine disinfection of cooling towers or superheating of water systems may be cost ineffective because of accelerated metal corrosion and replacement of the equipment (8).

Other investigators have stated that although previous studies have shown relationships between Legionella species and protozoa and between Legionella and cyanobacteria, such relationships were not observed in cooling towers implicated in an outbreak of Legionnaires’ Disease (31). These investigators also found that the total bacterial population was also more active in cooling towers routinely treated with biocides. They suggested that biocides reduce the density of Legionella and other bacteria in cooling tower water by that the remaining population is more active since there is less competition. They concluded that checking only for total non-Legionella bacteria is not a recommended procedure if Legionella are suspected, because it may produce a false sense of security.

What some building owners are currently doing to reduce their liability.

Some facilities engineers send in water samples for testing. Test reports are sent to the appropriate individual at each company along with information describing how to interpret the test result. Companies are contacted by telephone if cooling tower or hot water system counts are excessive. If no Legionella are observed, the count is reported as less than 10 per milliliter; the sensitivity limit of the test. Owners are advised to monitor trends in test results, not one-time sample results (unless the number is over 1,000 per milliliter), in order to decide the most appropriate strategy for their particular situation.

It is my observation that many cooling tower owners increase biocide treatment or disinfect their towers when the counts reach 200 per milliliter. There is a difference of opinion over the number of Legionella counts that should trigger disinfection of mechanical equipment. Some investigators claim that 1 Legionella bacterium per milliliter is excessive, others in the United States suggest 500-1,000 per milliliter as a more reasonable number.

Suggested guidelines for disinfection.

The State of Wisconsin and the EPA outline disinfection methods that have effectively removed Legionella from building water systems. The State of Wisconsin recommends a cooling tower shock treatment with 50 ppm free residual chlorine followed by a non-sudsing detergent, with maintenance of 10 ppm free residual chlorine for 24 hours following the initial shock dose, which is repeated once (34). Swimming pool chlorine is added before automatic dishwasher detergent (dispersant). This is a modification of the original Cooling Tower Institute suggested decontamination method (6). Details of the procedure must be consulted before decontamination is begun.

The EPA, which deals with Legionella contamination of domestic plumbing and potable water, recommends various free residual chlorine levels, ultraviolet light and/or maintaining a water temperature of at least 55°C or (130°F) for building potable water systems. However, measures to prevent scalding will be required at these temperatures. Hot water systems are usually decontaminated by heating to 175°F for one hour, although the American Water Works Association chlorination method has also been used (3). These procedures must be understood before potable water disinfection is begun. It is often best to have a professional water treatment company do the disinfection. The procedure is labor intensive, but it does not involve expensive chemicals.

Review of a field research project involving commercial and industrial towers.

In 1987, 1 co-authored a paper which included a statistical analysis of Legionella DFA tests on 1,336 samples from 472 cooling towers owned by 209 companies (17). Some companies had cooling towers at several locations around the United States, others had only one site. Samples came from 25 states within the continental United States. Thirty-seven cooling towers in this investigation were routinely sampled. The sampling frequency ranges from bimonthly tests per cooling tower to monthly tests per tower. DFA counts ranged from none seen (less than 10 per milliliter) up to 100,000 per milliliter of cooling water sample.

When the Legionella counts from all 1,336 test samples were grouped into four categories, 46% of the samples had no detectable Legionella, and 90% of the samples had counts less than or equal to 200 per milliliter. Only 10% of the samples had counts that would be considered significant by some researchers. Only 3% had counts over 1,000 per milliliter [1 million per liter] of cooling tower water sample. Legionella was not found to be ubiquitous in these routinely maintained cooling towers.

RANGE:< 10 TO 100,000 per ml.

<10. 46%.
10-200. 44%.
201-1,000. 7%.
> 1,000. 3%.

Routine biocide treatment effects on Legionella counts were also investigated. Most cooling towers were routinely treated with a combination of quaternary and organo-sulfiir compounds added at a rate of 40 ounces per 1,000 gallons of cooling tower water. In many cases, increasing monthly counts caused many cooling tower operators to increase the dosage of routine biocide treatments. This action may have kept counts in those cooling towers to a moderate level and therefore reduced the need for emergency disinfection.

I have observed that clean cooling towers and newly commissioned cooling towers containing little or no algae tend to harbor higher numbers of Legionella. Most cooling towers with the highest Legionella counts are not biofouled with other bacteria or algae.

Field research conclusions.

Three observations were noted during this investigation (17):

First, routine monitoring of cooling tower water for Legionella provided significant, useful information. When Legionella counts began to increase, additional biocide was added to effectively control the build up of excessive numbers of Legionella.

Second, it was clear that routine biocide treatments alone did not prevent excessive growth of Legionella in some of the cooling towers. Samples from some towers that were not monitored frequently and did not get observed during the investigation.

Third, complete cooling tower disinfection, using the recommended chlorination protocol, did not prevent regrowth of Legionella in some cooling towers two months after the decontamination.

Routine cooling tower water sample monitoring was the only way operators could tell when to add more biocide to control increasing numbers of Legionella.

Cooling Tower Sampling Instructions.

This sampling procedure is based on information about how people acquire Legionnaires’ Disease. This procedure offers no guarantee that personnel will avoid contamination by Legionella. Wear a N-100 HEPA elastomeric respirator or PAPR and gloves/gown during sampling if you suspect heavy Legionella contamination. Please note: Do not put dirt or debris into the sample bottle. These recommendations are based on over 39 years of Legionella field testing experience. If you want sample bottles available quickly, consider purchasing: Thomas Scientific CAT# 1206F61, CS 48, 120mL HDPE Packer bottles.

Sample Procedure:

(1) Before going to get the sample, use a ballpoint pen to print on the sample bottle label; the source of the sample and the date the sample was taken.

(2) If sampling a domestic water system (water line, shower head, hot water heater, heat exchanger, sink, fountain, spa, humidifier, etc.), obtain a first draw sample from the system and follow steps 4, 5, 6, and 7 below.

(3) If sampling a cooling tower or evaporative condenser, obtain a sample from the tower bulk water circulating line and follow steps 4, 5, 6, and 7 below. This sample should represent water in the tower drift. Do not sample dirt from the bottom of the sump or biofilm material.

(4) Make sure that the 4-ounce (120 ml) bottle is filled (110 ml) to just below the vertical threads and tighten the cap securely.

(5) Rinse off the outside of the sample bottle, put the sample label on the bottle and wash your hands with soap and water.

(6) Put the labeled bottle(s) in a return sample box along with a chain of custody document with your institution’s name, contact person name, email address, telephone number and billing/PO information

(7) Return sample bottle(s) at ambient temperature as soon as possible to our lab at: DR RICHARD GILPIN LLC LAB – 2515 BOSTON ST, SUITE 408 – BALTIMORE, MD 21224.

State of Wisconsin Disinfection Protocol (34).

“This protocol is for emergency treatment of air conditioning and industrial cooling towers, evaporative condensers and evaporative coolers as well as open circulating water systems including circulating pumps, refrigerant condensers and interconnecting piping which have been associated with an outbreak or a cluster of Legionnaires’ Disease…. These recommendations do not apply to closed recirculating systems, such as chilled water systems in which the water does not have direct contact with the air.” An abbreviated summary of the procedure is given below:

1. Shut off the heat source of refrigeration machines and the fans.

2. Close building air intake vents within at least 30 meters (100 feet) of the cooling tower until after the cleaning procedure is completed.

3. Continue operating the equipment’s recirculating water pumps but stop regular chemical treatment of all types.

4. Add an oxidizing disinfectant to give 50 ppm free residual chlorine. (For every 1,000 gallons of water in the system: Use 1/ 8 pound od calcium hypochlorite [HTH]; or 1&1/2 pints of [5% sodium hypochlorite] household bleach; or 3/ 4 pint of [10% sodium hypochlorite] liquid swimming pool chlorine or laundry bleach).

5. Maintain a 10 ppm of free residual chlorine in water return­ing to the cooling tower for 24 hours. Adjust pH to within 7.5- 8.0. Add automatic dishwasher compound such as Cascade™, Calgonite™ or equivalent at a dosage of 10-25 pounds per thousand gallons of water in the system.

6. Drain and flush entire system into a sanitary sewer system.

7. Refill the system with water and repeat the 50 ppm slug dose of chlorine and dispersant. Maintain the free residual chlorine level at 10 ppm for another 24 hours.

8. Drain the system into a sanitary sewer and mechanically clean the cooling tower, including screens and refill system.

9. Add chlorine to maintain 10 ppm free residual chlorine for one hour.

10. Drain the system and refill with clean water and return cooling tower to service


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