|Brenner et al., 1979
Legionella ( Legionella ) are a genus of rod-shaped bacteria from the Legionellaceae family. They are gram-negative and non- spore-forming bacteria that live in water and are motivated by one or more polar or sub-polar flagella (flagella). Legionella are to be regarded as potentially human pathogens . More than 48 species and 70 serogroups are currently known . The most important species for human diseases is Legionella pneumophila (proportion of around 70% to 90%, depending on the region), it is the causative agent of legionellosis or legionnaires' disease .
A special feature of many species of the Legionella genus is the high proportion of branched fatty acid chains in their membrane lipids . For example, in Legionella pneumophila, the proportion of branched chains is 64%.
The optimal living conditions for legionella are:
- Fresh and salt water
- Fresh water replenishment
- long dwell time
- Temperature range 25 ° C to 50 ° C
Effects of the different temperature ranges on the reproduction of legionella:
|Effect on the rate of reproduction
|up to 20 ° C
|very slow propagation
|from 20 ° C
|Multiplication rate increases
|30 ° C to 45 ° C
|from 50 ° C
|hardly any increase
|from 55 ° C
|no further increase possible
|from 60 ° C
In a study by the Helmholtz Center for Infection Research (HZI) in Braunschweig, it was shown that the bacterial pathogen Legionella pneumophila reproduces even at water temperatures between 50 and 60 ° C. The researchers believe that further studies should clarify the consequences for the management of hot water systems, air conditioning systems and cooling towers.
Occurrence of legionella
Legionella occur wherever warm water offers optimal conditions for their reproduction. They are viable in the temperature range from 5 ° C to 55 ° C, from 60 ° C they become inactive after a few minutes. Corresponding conditions can exist, for example, in
- Hot water production and hot water distribution systems
- Water tanks and boilers
- Cold water supply lines with long downtimes (e.g. after a long vacation or moderately used fire extinguishing lines with drinking water connection)
- Cold water supply lines with external heat exposure or to thermal mixers
- Dead lines
- Swimming pools
- public showers (e.g. school showers )
- Tub baths and ward baths
- Air washers for air conditioning systems
- Cooling towers
Transmission of legionella to humans
A transmission of legionella is in principle possible through contact with tap water if the legionella gets into the deep lungs.
Not every contact with legionella-containing water leads to a health hazard. Only inhalation of water containing bacteria as a bioaerosol ( aspiration or inhalation, e.g. when showering, with air conditioning, through lawn sprinklers and in whirlpools) can lead to infection.
Drinking water containing legionella is not a health hazard for people with an intact immune system.
An infection with Legionella is associated in particular with the following technical systems:
- Hot water supplies (e.g. in residential buildings, hospitals, homes, hotels, barracks),
- Ventilation systems ( air conditioning systems ) and humidifiers
- Bathing pools, especially hot tubs ( whirlpools )
- other systems that atomize water into water droplets ( e.g. mist generator , mist fountain )
Legionella was first discovered in July 1976 at the Bellevue-Stratford Hotel in Philadelphia (USA). There, 180 of 4,400 delegates fell ill at the 58th Veterans Congress of the American Legion ( Pennsylvania American Legion ). The disease claimed 29 lives, and although Congress began on July 22, it wasn't until August 2 that the health department realized that an epidemic was rampant. Despite immediate research, it took until January 1977 to isolate the bacterium from the lung tissue of a deceased veteran. By the end of the 1980s, 22 species were known, as well as 11 serogroups of Legionella pneumophila.
Due to the global spread of the problem, the World Health Organization issued a handbook in 2007 with recommendations that some countries had previously implemented.
A study from 2005 to 2010 in Berlin clinics showed that every second hospital was affected by Legionella. However, you are only required to report an actual illness. In September 2015, a case was reported at the Bremen-Ost Clinic .
The outbreak of a Legionella epidemic with the highest number of deaths in Germany occurred at the beginning of January 2010 in the Ulm area with 5 dead and 64 infected. The pathogen was the rod bacterium Legionella pneumophila of serogroup 1. The health authorities, in cooperation with the Technical University of Dresden, among others , identified the cooling towers belonging to a combined heat and power unit and a refrigeration machine in Olgastraße 67, near the Ulmer Central station . The system was installed in September 2009 and was in trial operation at that time. There was an outbreak in the Frankfurt (Oder) Clinic in 2003 with six infected people, two of whom died. The legionnaire's disease outbreak in Warstein 2013 was the case with 165 people and the largest number of infected people in Germany to date. Up to September 25, 2013, there were three fatalities.
Regulations in Germany
The current version of the German Drinking Water Ordinance (abbreviation TrinkwV 2001) (published on March 10, 2016) prescribes regular testing for Legionella. This applies to all entrepreneurs and other owners of drinking water installations with large systems for heating drinking water, provided that drinking water is dispensed from this in the context of a commercial and / or public activity and the drinking water is misted (e.g. in showers).
Hospitals, schools, kindergartens, hotels and nursing homes are the public operators of large systems for heating drinking water. These facilities are obliged to have Legionella tested at several representative sampling points once a year. What is new is the obligation to examine other groups, which has only existed since the end of 2011, including owners / landlords of apartment buildings, housing associations and property management companies. For these, the required examination interval is three years. The initial examination had to be completed by December 31, 2013.
Both the drinking water sampling and the analysis must take place in the accredited area, ie the water sample must be taken by appropriately trained specialists who are involved in the quality management system of an ISO / IEC 17025 accredited test laboratory. The laboratory must also be approved for the microbiological analysis of drinking water in accordance with Section 15 (4) of the Drinking Water Ordinance and published in one of the state lists of the federal states.
In the Drinking Water Ordinance, a technical measure value of 100 colony-forming units (CFU) per 100 ml is specified for legionella. If this value is found to be exceeded during an examination, this must be reported immediately to the responsible health department. In accordance with Section 16 (7) of the Drinking Water Ordinance, there are also further obligations and technical measures such as an on-site risk analysis and, if necessary, a comprehensive renovation of the drinking water installation.
Technical measures to reduce the growth of Legionella
Applies to the construction and operation of drinking water heating and drinking water supply systems in Germany the DVGW - 551 Practice W has a temperature of at least 60 ° C above "technical measures to reduce the growth of legionella" of April 2004. After that under normal operation at the outlet of hot water generation plants held and can also be adhered to in large systems. In systems with circulation lines, the hot water temperature in the system must not fall by more than 5 K compared to the outlet temperature. In addition, drinking water (cold) should be kept as cool as possible and protected against undesirable warming, e.g. B. be protected from sunlight or nearby heating cables.
The storage of hot water in a water boiler with temperatures below 60 ° C can lead to an increase in Legionella. Offer a remedy
- special "legionella circuits" that automatically heat the memory contents higher at regular intervals,
- Coiled pipes running through the storage tank, in which the cold drinking water is heated
The disadvantage of heating drinking water above 55 ° C is that above this temperature more and more dissolved lime precipitates and can be deposited on the pipe walls of the heat exchanger. In special " fresh water stations " outside the storage tank, the stored hot water can heat the fresh, cold drinking water with the help of a powerful plate heat exchanger , fresh cold water mixed in can keep the temperature below 55 ° C (temperatures of up to 40 ° C are sufficient for bathing and showering).
With a content of 100 CFU (colony-forming units) / 100 ml, drinking water is considered to be contaminated (low risk of infection, "technical measure value"), immediate action is required from a contamination greater than 10,000 CFU / 100 ml. Worksheet W 551 speaks of a "Extremely high contamination" and demands immediate measures such as B. disinfection of the pipe network or the imposition of a shower ban.
Detection and counting of Legionella in drinking water
The analysis within the scope of the examination obligation is carried out using the classic microbiological detection method. Each of the drinking water samples previously taken professionally at several representative locations is divided up in the laboratory and examined in two parallel approaches in accordance with ISO 11731: 1998 and DIN EN ISO 11731-2: 2008. In direct preparation, 1 ml of the sample, divided into twice 0.5 ml each, is placed in two Petri dishes or plates with solid GVPC or BCYE nutrient medium ( agar ) and distributed there evenly with the so-called Drigalski spatula so that the sample volume is completely is absorbed by the agar.
The larger part of the initial sample (usually 100 ml, but volumes between 10 and 1000 ml are generally possible) is filtered in the second batch through a membrane filter with a pore size of 0.45 µm. The filter membrane is then treated with acid buffer in order to reduce the non-Legionella accompanying flora, then washed and placed on another Petri dish with GVPC or BCYE agar.
The agar plates from both batches are grown for ten days in an incubator at a constant temperature of 36 ± 2 ° C. At the end of this time, if there were living Legionella in the sample, the so-called colonies that grew during the incubation are counted as characteristic light spots on the dark agar and evaluated. The quantitative result is given in "colony-forming units" (CFU) based on 100 ml of sample. If 180 colonies are counted on the filter membrane after filtration of 100 ml, the result of the filtration batch is 180 CFU / 100 ml. In the direct batch, the colonies of the two individual plates are first added (corresponds to 1 ml sample) and then multiplied by 100. If, for example, two colonies have grown on plate A and one on plate B, the result of the direct batch is (2 + 1) * 100 = 300 CFU / 100 ml. The technical measure value of 100 CFU / 100 ml was thus exceeded.
The final result of the Legionella analysis is always the higher value determined from the two approaches, in the present example the value from the direct approach. In addition, it is noted from which batch volume the final result was determined (in the present case from 1 ml).
To confirm the analysis, at least five colonies are subcultured in parallel on both cysteine-containing medium such as BCYE agar and on a cysteine-free nutrient medium (BCYE-Cys, nutrient agar or blood agar) for at least two days at 36 ± 2 ° C. Since the amino acid cysteine is essential for Legionella, the detection is considered confirmed if the colony grows on the cysteine-containing medium, but not on the cysteine-free medium.
In Austria, the analysis and evaluation of Legionella is quality-assured by TÜV Austria Hygienic Expert or the Agency for Health and Food Safety (AGES) in accordance with ÖNORM EN ISO 11731-2.
Measures to reduce legionella
With ultrafiltration , the pathogens are removed mechanically from the water. The modules consist of bundled tubular ultrafiltration membranes cast into cladding tubes at both ends . The pore size of the membrane is 0.01 to 0.05 µm.
In order to achieve the separation effect, the water is directed to the outside through the wall of the membrane capillary . The pure water is collected by the surrounding jacket tube of the module and passed through the side connection to the supply system as bacteria-free and low-virus water. The device must be cleaned regularly, this is done by flushing the filtration system forwards and / or backwards. The retention of microorganisms can be demonstrated by means of an integrity test of the membrane. According to DIN EN 14652 (systems for the treatment of drinking water inside buildings - membrane filter systems - requirements for execution, safety and testing, German version EN 14652: 2005 + A1: 2007), point 6.6, is for the protection of ultrafiltration systems with automatic backwashing and automatic Integrity test, a backflow preventer for protection is sufficient. Quotation from point 6.6 Backflow prevention "The system must have an upstream backflow preventer according to EN 1717".
Legionella are inactivated or killed in a short time at a temperature of more than 70 ° C. During thermal disinfection, the water heater and the entire pipe network including all tapping points (e.g. water taps) are therefore heated to more than 71 ° C for at least three minutes. The specifications of the DVGW must be observed here. The set target temperature in the hot water storage tank should be 60 ° C, the cooling of the circulation line must not be greater than 5 ° C.
Modern heating controls for small heating systems increase the storage tank temperature briefly at least once a day or at short regular intervals, whereby the hygienic aspects with regard to sense and benefit must be checked in each individual case.
With thermal disinfection, the risk of scalding at the tapping points must be observed. There are risks in the incorrect implementation of thermal disinfection and in the lack of lasting effectiveness. Disadvantages are the increased aging of the pipe material and the seals and the possible transfer of heat into the cold water network. The thermal disinfection naturally only covers the hot water network. Legionella can also multiply in cold water if the cold water pipes heat up to over 20 ° C. The causes are often structural defects such as the laying of drinking water pipes in the floor with underfloor heating , stagnation due to pipes that are too large, joint laying in supply lines with hot water pipes or heating pipes without sufficient insulation.
It should be noted that above about 60 ° C (depending on the ingredients and especially the hardness of the drinking water) lime precipitates in the pipe network and can cause problems, depending on the pipe material used. The iron materials previously used proved to be particularly problematic. Limescale deposits can lead to the closure of galvanized steel pipes within a few decades. This should no longer be used for hot water pipes.
The Aachen concept is a process developed jointly by the Aachen Clinic and the Kryschi Wasserhygiene company in 1987 to protect against Legionella by exposure to ultraviolet light (UV light). According to the technical regulations DVGW W 551 (April 2004 edition) it is the only alternative to thermal solutions. It is used where elevated temperatures are not possible or not wanted.
The concept requires decentralized UV devices close to the delivery points. The changes made in August 2007 in the UBA list to Section 11 of the Drinking Water Ordinance Part II must be observed. The advantage of this method is that no chemical additives are used. The lack of depot effect is compensated for by periodic pipe flushing.
Permanent disinfection can also be carried out with chemicals approved for this purpose; limit values and the formation of disinfection by- products must be observed (see list of the Federal Environment Agency for Section 11 of the Drinking Water Ordinance Part Ic). However, chemicals have not proven successful as a permanent solution.
In shock disinfection, chemicals are used in high concentrations, which are then removed from the pipeline network by rinsing. During the measure, it must be ensured that no drinking water is withdrawn. Disinfectants that are not listed by the Federal Environment Agency can also be used for shock disinfection, such as B. hydrogen peroxide (H 2 O 2 ).
Electrolytic production of chlorine on site
These processes work with electrolysis cells and produce chlorine gas or " hypochlorous acid " (sodium hypochlorite).
The on-site production of neutral sodium hypochlorite by electrochemical activation by means of membrane cell electrolysis (the name of the disinfectant produced in this way is anolyte) is a new process and has been included in the list under Section 11 TrinkwV 2001 Part II since August 2007. The procedure is described in worksheet W229 of the DVGW (Section 6.5.2). According to the list of §11 TrinkwV 2001 Part Ic, the sodium hypochlorite solution must meet the purity requirements of DIN EN 901.
Anolyte is able to break down biofilm . Neutral anolyte contains only small amounts of chlorine gas and therefore forms noticeable amounts of chloroform only with a strong excess of acetyl compounds (proteins, biofilm matrix), which are gradually converted to chloroform with Cl 2 (haloform reaction). After the breakdown of superficial biofilm layers, chloroform can no longer be detected in anolyte-doped water.
The Drinking Water Ordinance specifies a minimization requirement. It should not be disinfected for prophylactic reasons. In addition, the deficiencies are to be remedied in the shortest possible disinfection time and then switched to regular operation.
Microbiocidal reaction effect
In Germany, only disinfectants may be used for the biochemical disinfection of drinking water that are listed in the list (Part Ic) of Section 11 of the Drinking Water Ordinance kept by the Federal Environment Agency: calcium and sodium hypochlorite , chlorine , chlorine dioxide and ozone (as of August 2007).
In Germany, direct or indirect evidence of Legionella ( Legionella sp ) must be reported by name in accordance with the Infection Protection Act , provided the evidence indicates an acute infection. The obligation to notify primarily concerns the management of laboratories ( IfSG).
In Switzerland, the positive and negative laboratory analysis findings to Legionella is ( Legionella spp. ) For laboratories reporting requirement and that after the Epidemics Act (EpG) in connection with the epidemic Regulation and of the Regulation of EDI on the reporting of observations of communicable diseases of man .
- Legionella test procedure in approved drinking water laboratories (PDF file; 74 kB)
- Combating legionella through silver electrolysis Article from IHKS-Fachjournal (edition 2008)
- Technical rule worksheet W 551 Drinking water heating and piping systems; Technical measures to reduce the growth of Legionella; Planning, construction, operation and renovation of drinking water installations (PDF file, 390 kB)
- Legionella circuit How useful is the legionella circuit and thermal disinfection?
- T. Kaneda: Iso- and anteiso-fatty acids in bacteria: biosynthesis, function, and taxonomic significance. In: Microbiol. Rev. 55 (2); June 1991: pp. 288–302, PMID 1886522 (free full text access )
- Bavarian State Office for Health and Food Safety: Legionella - the most frequently asked questions. Retrieved October 17, 2017 .
- René Lesnik, Ingrid Brettar, Manfred G Höfle: Legionella species diversity and dynamics from surface reservoir to tap water: from cold adaptation to thermophily. In: The ISME Journal. 2015, doi: 10.1038 / ismej.2015.199 .
- A. von Graevenitz: Die Familie der Legionllacaea - Legionellose, in: Textbook of Medical Microbiology, edited by Henning Brandis and Gerhard Pulverer
- - ( Memento of the original from November 26, 2015 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.
- Sibylle Huebner-Schroll: Augsburger Expert: "unsettling accumulation" In: Augsburger Allgemeine , January 15, 2010.
- Stephanie Schuster: Legionella bacteria has been identified. In: Augsburger Allgemeine , January 15, 2010.
- City of Ulm: Archived copy ( memento of the original from March 31, 2017 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- Katrin Bischoff, Jens Blankennagel: Death while showering. In: Berliner Zeitung , August 1, 2003.
- Legionella in Warstein claim third death. WAZ , September 24, 2013, accessed September 25, 2013 .
- Approved inspection bodies according to § 15 Drinking Water Ordinance
- Process of microbiological legionella analysis in accordance with the Drinking Water Ordinance in approved test laboratories (PDF file; 74 kB)
- Das Aachener Konzept (published in sbz, 46th year 1991, issue 17, pp. 44–48) ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. (PDF file; 80 kB), p. 1
- Legionella problem in drinking water (FLUGS-Fachinformationsdienst am Helmholtz Zentrum München, German Research Center for Health and Environment) ( Memento of the original from December 9th, 2008 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF file; 178 kB), p. 8
- Legionnaires. RKI advisor. Robert Koch Institute, September 5, 2019, accessed on March 18, 2020 : "Notification obligation according to IfSG"