Water and Food Department - Treatment Suggestions: Legionella Prevention — Culture Method

Legionella Prevention — Culture Method

“The bacteria of the Legionella genus are found in natural aquatic environments and in artificial systems, such as supply networks/water distribution, building networks of hot and cold water, air conditioning and cooling systems (cooling towers, evaporative condensers and humidifiers) found in buildings, including hotels, spas, shopping centres and hospitals. They can also be found in ornamental fountains and recreational tanks, like hot tubs.”

Exposure to the bacteria can cause respiratory infection, currently known as Legionnaires’ disease. It is important to distinguish the status of colonization of water systems by bacteria of the Legionella genus, from the occurrence of an event of Legionnaires’ disease.

There are no guide numbers for the concentration of the Legionella genus in water in colonies forming units per liter (cfu L), higher than what occurs Legionnaires’ disease and lower than the probability of occurrence is almost zero.”

In: Prevention and Control of Legionella in water systems, the Portuguese Quality Institute in partnership with EPAL, Empresa Portuguesa das Águas Livres, SA, 2nd Edition 2014.

Legionella spp	Matrix	Unit	Reference Conditions
Legionella spp	Water	(cfu/L)	Concentration of less than 100 cfu/L, except in the case of research in cooling towers tanks, where must a lower concentration of 1000 cfu/L. be registered. Absence of Legionella pneumophila

Reference data and corrective actions in building networks

“Usually, for building network water, it is considered that a Legionella analysis, from an operation and maintenance point of view, is unfavourable when the concentration of Legionella spp., is ≥1000 cfu/L, which corresponds to an alert level, making it necessary to collect new samples, review the water treatment program, assess the risk and if necessary clean and disinfect the system or implement chemical shock treatments and/or thermal, subsequently evaluating the effectiveness of the implemented measures.

For amounts lower than 100 cfu/L of Legionella spp., the system is considered to be under control. However, these values are not identical throughout the literature and should be only taken as a reference.

Regarding respiratory therapy equipment, the limit number is 0 cfu/L, because the risk is so great.”

In: Prevention and Control of Legionella in water systems, the Portuguese Quality Institute in partnership with EPAL, Empresa Portuguesa das Águas Livres, SA, 2nd Edition 2014.

Chemical Disinfection

Chlorinate the water in the cold water storage tank, adding sodium hypochlorite until you reach a level of residual free chlorine of 20 to 50 mg/L; the next step is to re-circulate the chlorinated water in the entire system, successively opening all taps and showers until you detect an intense smell of chlorine;

Close all exits, putting the system on standby for approximately one hour to reach a level of residual free chlorine of 50 mg/L or two hours a level of residual free chlorine of 20 mg/L;

Perform routine analysis until the absence of bacteria of the Legionella genus (and other bacteria) is detected; if such does not happen, repeat the procedure described above;

Facing the occurrence of colonization of the building network’s water by Legionella pneumophila, it is essential to avoid inhalation of aerosols and, therefore, impose a prohibition of the use of showers, hot tubs, etc.

If the water heaters and storage tanks are contaminated it is necessary to disinfect them before cleaning them;

All personnel involved in these procedures must be highly specialized and properly trained, wearing individual protective gear.

Thermal Disinfection

Consists typically in increasing the temperature of the water heaters or hot water tanks up to 70° C, while circulating the water through the system for one hour.

In points of consumption, faucets or showers, the water temperature should be 60° C or higher for at least five minutes after opening, and preferably at the endpoints;

The heat-disinfection should be performed weekly along with the bacteriological examination until the system is no longer under suspicion;

For this procedure to be effective it is best if the hot water system is well insulated and allows to increase the temperature throughout the system up to 60ºC for at least one hour;

Upon the occurrence of one or more cases of Legionnaires’ disease, follow all the procedures already covered for the cooling towers, like collecting samples at critical points for Legionella pneumophila research and carry out disinfection and cleaning of the entire network, using specialized and qualified staff to do so;

All inspections, monitoring, maintenance and operations should be registered in a manual for easy access.”

In: Doença dos Legionários, Guia Prático, Direção-Geral da Saúde & Direção-Geral do Turismo, Lisboa 2001.

Reference data and corrective actions for cooling towers and similar analogue devices, according to the microbiological analysis of Legionella:

Legionella (cfu/L) Count	Recommended Action
100<1000	Review the maintenance program and make the necessary corrections
100<1000	Conduct a new sampling after 15 days
1000<10000	Review the maintenance program, in order to establish corrective actions to reduce the concentration of Legionella
1000<10000	Conduct analysis after 15 days. If the result is <100 cfu/L, you should collect new samples after one month. If the result of the second sample is <100 cfu/L continues with the planned maintenance
1000<10000	If one of the previous samples registers numbers >100 cfu/L, you should review the maintenance program and make the necessary structural changes
1000<10000	If the numbers are higher than 1000 cfu/L, you should clean and disinfect the system (a) and collect new samples after 15 days
>10000	Shut down operations and, if necessary, drain the system
> 10000	Clean and perform a deep treatment according to (a), before restating operations
> 10000	Collect new samples after 15 days
(a) Cleaning and disinfection in case of detection of Legionella.

Chlorinate the system water to get at least 20 mg/L of free residual chlorine and add bio dispersants and compatible anticorrosive in adequate amount, keeping all fans off and, when possible, any opening, to prevent the output of aerosols;

Re-circulate the system for 3 hours, measuring the level of free residual chlorine hourly, replacing the lost amount;

Neutralize the chlorine and re-circulate the water in the same manner as the previous point;

Empty the system and rinse with pressurized water;

Clean the system’s surfaces with detergent and pressurized water and rinse;

Introduce chlorine in the water flow in sufficient amount to reach 20 mg/L of free residual chlorine, adding anticorrosive compatible with chlorine in adequate measure. Maintain for two hours, checking the free chlorine level every 30 minutes, restoring the amount lost. Re-circulate the water through the system, keeping the fans off and the openings closed;

Neutralize the chlorine and re-circulate the water in the same manner as the previous point;

Empty the system, clean it and add the maintenance disinfectant. When the disinfectant is chlorine, you should maintain a level of 2 mg/L of free residual chlorine and add an anticorrosive compatible with chlorine in adequate measure;

The removable parts should be cleaned and submerged in a solution containing 20mg/L of free residual chlorine, for 20 minutes, and subsequently rinsed in abundant cold water. Elements difficult to disassemble or to access should be sprayed with the same solution during the same amount of time. As for equipment whose size or design does not enable spraying, cleaning and disinfection must be carried out through electric nebulising;

Subsequently, proceed with the usual maintenance measures.

Reference data and corrective actions for heated water systems for recreational use according to the microbiological analysis of Legionella

Nº Legionella spp/1000mL	Interpretation
<10^2	Under Control
≥10^2 to ≤10^3	Collect new samples for analysis and maintain increased vigilance
≥10^2 to ≤10^3	Advise the system manager to empty, clean and disinfect the system
≥10^2 to ≤10^3	Review the control measures and risk assessment; develop the identified corrective actions
≥10^2 to ≤10^3	After filling the basin, perform further analysis on the next day, and after 2-4 weeks
10^3	Immediate shutdown; evacuate the public within the vicinity of the basin
10^3	Proceed to shock disinfection of 50 mg/L of free chlorine in circulation for one hour
10^3	Drain, clean and disinfect the basin
10^3	Review the control measures and risk assessment
10^3	After filling the basin, perform further analysis on the next day, and after 2-4 weeks
10^3	Maintain shutdown until Legionella is no longer detected and the risk assessment is positive

In: Prevenção e Controlo de Legionella nos Sistemas de Água, Instituto Português da Qualidade 2º Edição 2014

(Health Protection Agency (UK) “Management of Spa Pools – Controlling the Risks of Infection” March 2006.