Reaction Limits
Guide to reaction limits for hot water systems in homes.
It is assumed that the risk of Legionaire’s disease is greatest when many Legionella bacteria are present in the examined water test(s). However it is not possible to indicate any accurate connection between the observed quantity of Legionella bacteria in a test and the risk of Legionair’s disease.
There are various reasons for this:
- The concentration of Legionella bacteria in a water system is not necessarily constant. The result of a single test must be considered as a snapshot.
- Water from different tap places in the same system may hold great variety in its concentration of Legionella bacteria exclusively depending on local conditions as water consumption and the materials used for the pipes and hoses leading the water.
- The virulence holds great variation (the probability to cause infection) among Legionella strains. A low population of highly virulent strains may however exceed a far greater health risk than a high population, with a less virulent strain can do.
- The suspectibility of the disease depends on the health condition of the person and his/ her resistance to the infection.
- Aerosol formation, intensity and duration of the effect and the presence of Amoebas in the water may matter to the infection risk.
Reaction Limits
In the following table it is stated proposed reaction limits by identification of Legionella in the hot water systems in homes.
Due to above mentioned reservations, these limits are indicative only, and therefore it can happen that some water systems in which a lower concentration of Legionella bacteria ( <1000 cfu/liter) can cause infection.
Proposed reaction limits by identified Legionella in hot water systems in homes
| Legionella cfu/liter |
Actions impact/reaktion |
|
10 - <1000
|
Low number - Though indicating that Lefionella bacteria can crow ind the system.
|
|
1000- <10.000
|
Low to a moderate number of bacteria.
It is to be considered whether individual improvement of the system should be made such as the operation temperatures and removal of dead ends.
|
|
10.000 - <100.000
|
Relatively high populations of bacteria.
It is to be considered whether improvements on the systems and/or disinfection should be made. The situation is being monitored.
|
|
>100.000
|
Very high bacteria population.
The system must be reviewed with remedical measures.
|
Modified according to Morris GK & Shelton BG. 1994.
cfu = colony forming units.