Legionella bacteria

Legionnaire's disease
Pontiac fever

Legionella in water systems

Combination of factors
Sensitive areas in tap water systems in buildings
Risk assessment in special types of buildings and installations
Occurrence of legionella in water systems
Action in suspected cases
Conventional methods are inadequate

Legionella bacteria

Legionella bacteria occur naturally in small concentrations in both watercourses and ground water, and it will not be possible to eradicate them. Legionella can cause Legionnaires’ disease, a serious form of pneumonia that can result in death, and Pontiac fever, which causes symptoms similar to influenza.

Up to 48 different species of the legionella bacterium have been identified, and around half have caused illness. Legionella pneumophila is the most common of these species both in the environment and in connection with illness. In purification plants there is no practical means of removing the small quantities of bacteria involved. The water supply therefore introduces legionella bacteria into our building water systems. This is where we must put systems in place that prevent the bacteria from multiplying to concentrations at which they can make us ill. Legionella bacteria survive freezing and multiply at temperatures between 20° and 50°C, with an ideal growth temperature at around 38°C.

Legionnaire's disease

Spread of infection
People catch the dangerous lung disease Legionnaires disease and the influenza-like disease Pontiac fever by inhaling water mist (water in aerosol form) containing legionella bacteria. Showers are therefore a common source of infection, but aerosols are also formed around other tap points. Some researchers think that the most common way of getting legionella in the lungs is through aspiration, i.e. when you drink infected water and some of it goes down the wrong way by mistake. Legionella is spread in dangerous concentrations through water systems, which we deal with in detail below, and also via whirlpool baths, where the water temperature is ideal and the air bubbles generate a water mist, in wet cooling towers, in decorative fountains, in high-pressure washing appliances and in ice machines in hotels and hospitals. The risk is dose-related, i.e. it is proportional to the bacteria concentration of the water. A reduced infections/immunological defence increases the risk, as does smoking. It is unclear why some people who are exposed to infection get Legionnaires’ disease while others get Pontiac fever and yet others remain healthy. The infectious dose and the individual’s health status are most probably determinants. Legionnaires’ disease and Pontiac fever are not spread from person to person.

Incidence
Legionella is a notifiable disease under the Communicable Diseases Act in Sweden, and around 100 cases are reported each year. The actual number of cases is probably about 10 times higher than the reported figures, as it is difficult to distinguish the disease from other types of severe pneumonia and most cases therefore remain undetected. Legionnaires’ disease caused 2 to 5 per cent of the pneumonia cases seeking hospital care. Throughout Europe there may be some 50,000 cases each year, or 100 cases per million inhabitants, according to estimates by EWGLI (the European Working Group for Legionella Infections).

Course of the disease
The incubation period is generally 5-6 days, but everything from 2-10 days occurs. Legionnaires’ disease presents as a severe pneumonia, generally with high fever, headache and muscle pain. There is often diarrhoea. The clinical picture is often serious, especially if the patient’s immune system is suppressed. Serious pneumonia requiring respirator care is not unusual and some information indicates that 5-20 per cent of patients seeking hospital care die. The disease can be treated using antibiotics, but the preparations used for ordinary pneumonia have no effect. It is therefore very important to make the right diagnosis so that the right kind of antibiotic is used. Recovery can take years.

Pontiac fever

Pontiac fever is an influenza-like illness with headaches, muscle pain and fever. These symptoms are usually present within 12 to 24 hours of exposure. As the symptoms of Pontiac fever are the same as for a severe cold or influenza individual cases of the disease are rarely diagnosed correctly. Generally a correct diagnosis is only made in disease outbreaks when numbers of people are affected at the same time. It is, however, known that Pontiac fever infects many more exposed people than Legionnaires’ disease. For instance, more than 90 per cent of people exposed to legionella bacteria in whirlpool baths catch Pontiac fever. A person with the disease generally recovers within 3-5 days without any special care or medication.

Legionella in water systems

Combination of factors

Low concentrations of legionella bacteria enter the water systems in our buildings via water from water works. Bacteria growth is affected by:

• Stationary water.
• Sediment, amoebas and biofilms in pipes that provide protection and nourishment.
• Time.
• Water temperatures between 20°C and 50°C.
• The ideal temperature for bacteria growth is 35-45°.
• In that temperature range the bacteria divide every 15 minutes and growth is extremely rapid.
  Legionella occurs most in hot water, but the bacteria can also multiply in cold water. The growth risk increases if cold water is heated to over 20°C and when water is stationary in insufficiently insulated pipes with a high ambient temperature. In mixers legionella bacteria can also be transferred from one side to the other.

Sensitive areas in tap water systems in buildings

Stationary water at an ideal temperature can gather in places like distribution pipes with long branches, long dead end pipes that have not been shortened and mixers and shower hoses in rooms that have been empty for some time. Poor water circulation also leads to the formation of biofilm, where legionella bacteria thrive. Due to poor insulation, cold water may be unintentionally heated up by hot water.

Stationary water at an ideal growth temperature may be found in:

• Calorifiers, or water heaters.
• Dead end or dummy pipes, known as dead water pipes, may, for instance, be formed when a mixer is removed but the connection pipe is retained. This creates a dead end pipe with stationary water. Some pipes may also have been installed in view of future needs that may never have arisen subsequently. Dead end pipes are also formed as a result of incorrectly designed distribution pipes. In buildings that are often altered, such as hospitals, there is a considerable risk of creating dead end pipes, either intentionally or through negligence.
• In distribution pipes with long branches.
• In rooms that are empty at times: for example, hospitals, hotels and housing (during holidays) often have rooms that are not used at certain periods. This also means that when mixers in showers and other tap points in places like hospitals are used at long intervals there is a considerable risk that dead end pipes are created either intentionally or through negligence.
• Conventional mixers have made the situation worse because water at the perfect temperature for bacteria growth is left in the mixing chamber, the shower hose and the shower head.
• Biofilm also forms on the inside of water pipes where amoebas of different kinds take refuge and where legionella then colonise the amoebas and the biofilm. Legionella is mainly found in hot water, but the bacteria can also multiply in cold water, which often reaches 20°C when it is stationary in insufficiently isolated pipes that are heated up by hot water pipes or other heat sources.

Biofilm also forms on the inside of water pipes where amoebas of different kinds take refuge and where legionella then colonise the amoebas and the biofilm. Legionella is mainly found in hot water, but the bacteria can also multiply in cold water, which often reaches 20°C when it is stationary in insufficiently isolated pipes that are heated up by hot water pipes or other heat sources.

Risk assessment in special types of buildings and installations

Some buildings are more sensitive than others in terms of legionella:

• Hospitals: typically hospitals have large numbers of tap points on the same building floor. Problems of pressure variation are not unusual. In addition, there is a risk of long periods without water use in showers in patient rooms, for instance. The fact that patients frequently have reduced resistance is an additional element of risk.
  
• Housing: often a situation similar to hospitals.
• Hotels: lots of water outlets and risk for long periods of inactivity.
• Dentists’ offices.
• Public baths: whirlpool baths are a known legionella risk on account of water mist and the “right temperature.” Another risk factor is central mixers in shower rooms, where temperate water may be stationary in long pipes.
• Sports and exercise buildings and camping sites: see public baths.
• Manufacturing plants.
• Emergency showers and eye showers are examples of tap points with long inactive periods, where water at room temperature is stationary.
• Offices: high-rise buildings require particular care on account of pressure variations.
• Dwellings: the performance of circulation systems must be assured.
• District heating stations: greater focus must be placed on the performance of district heating stations. The protection of the water supply installation must also be reviewed. Tap water is a foodstuff that must be protected from unauthorised influences. Locked premises at district heating stations and similar facilities are an obvious measure.

Occurrence of legionella in water systems

The Swedish Institute for Infectious Disease Control (SMI) carried out a study in the early 1990s. It showed that legionella bacteria are found in both cold and hot water and in both one and two dwelling buildings as well as in complex buildings.

Similar results have subsequently been reported from other European countries. See the examples below:

The reason why such a large proportion of hospitals have legionella in their water systems is that there are lots of tap points that are often unused over weekends, for instance. Conditions in stationary water are favourable to bacteria, and once they have become established in pipes and fittings the bacteria are very difficult to get rid of. Growth is favoured by the biofilm almost always found on the inside walls of water tanks, water pipes and shower hoses. The situation is similar in hotels, which rarely have an average occupancy of more than 80 per cent and where certain rooms are often empty. However, the fact that legionella has not been found in a water supply at a particular time is unfortunately no guarantee. The bacteria enter along with drinking water and, if conditions are right in any part of the system, they can quickly multiply and colonise the whole system.

The same points are made in the action programme for cases of legionella infection occurring in care facilities or special residential homes that has been published by Stockholm County Administration/Stockholm County Council’s Central Hygiene Committee. All major buildings, such as hotels and hospitals, can probably be affected by problems with legionella bacteria in their water pipes. Water entering a building complex may be of a high standard, but factors like dead end pipes with stationary water and too low a water temperature favour the growth of legionella bacteria.

Action in suspected cases

Swedish Institute for Infectious Disease Control: Legionnaires’ disease is a notifiable disease under the Communicable Diseases Act. Cases are reported to the communicable disease control doctor in the county, to the Environmental and Public Health Department or equivalent in the Municipality and to the Swedish Institute for Infectious Disease Control. It is important that all cases of Legionnaires’ disease are investigated and that possible infection paths are examined. It must be possible to trace and eliminate the source of infection. When someone goes down with Legionnaires’ disease, preferably already when legionella is suspected, samples should be taken from the likely infection sources (often shower water) and checked for legionella bacteria.

The authorities’ requirements are general and, at present, no limit value has been set and therefore test sampling for legionella is not required. Accredited legionella analyses are carried out by the Swedish Institute for Infectious Disease Control and some other microbiological laboratories. Under the Environmental Code municipal environment and public health protection departments can order property owners to take action to minimise the incidence of legionella bacteria. All action must be combined with heating, ventilation and sanitation engineering work.

Conventional methods are inadequate

Conventional methods of disinfecting water systems do not give full and lasting protection. Flushing with high-pressure hot water and chlorination are only acute measures and do not give long-term protection, as new legionella bacteria are introduced into the building’s water system from the municipal water system. A continuous inflow of legionella bacteria requires continuous disinfection. The continuous methods that have been available until now do not solve the problem.

• They are unable to disinfect the whole system with lasting effect
• They require trained personnel and careful monitoring
• Both installation and operating costs are high
• Environmental risks and secondary health hazards also exist