Legionella: a new threat as the world re-opens?

By Cristian Carboni

Since April, controlling the spread of COVID-19 and limiting the damage to communities demanded the shutdown of hotels, resorts, camp sites, pools, offices and other buildings around the world. During the shutdown, many of these water systems experienced low to no flow, loss of disinfectant residual, and tepid water temperatures. Now, as many buildings begin to re-open, we are faced with yet another public health concern: an increase in Legionella amplification, common in these conditions, that can cause Legionellosis.

Legionellosis is a collection of infections that emerged in the second half of the 20th century, and that are caused by Legionella pneumophila and related Legionella bacteria. The severity of legionellosis varies from mild febrile illness (Pontiac fever) to a potentially fatal form of pneumonia (Legionnaires’ disease) that can affect anyone, but principally affects those who are susceptible due to age, illness, immunosuppression or other risk factors, such as smoking. Water is the major natural reservoir for legionellae, and the bacteria are found worldwide in many different natural and artificial aquatic environments, such as cooling towers; water systems in hotels, homes, ships and factories; respiratory therapy equipment; fountains; misting devices; and spa pools.

To avoid a dramatic increase in Legionnaires’ disease, there are several actions that building owners should take now and prior to returning buildings to full service to reduce hazardous conditions caused by the COVID-19 low building occupancy rates.

Generally, incoming water from the local water utility contains a disinfectant residual that limits biological growth in distribution piping and your building. In buildings with low water utilization and stagnation as a result of the COVID-19 shutdown, the disinfectant residual will be lost and with it, one of the critical barriers to bacteria amplifying. Bringing fresh disinfectant residual into the building will be an important step to reduce the likelihood of a Legionellosis outbreak.

Systems that are shut for an extended period and systems that have been shut down intermittently, such as cooling towers used for comfort or process cooling, need to be carefully managed to ensure continued application of biocides and to reduce the risk.

On April 21, the Pan American Health Organization (PAHO), the regional office of the World Health Organization, published the guidelines "Legionella Control in Repurposed Building or Spaces: Covid-19: Preparedness and Control.” The document urges the public to pay attention to the danger of Legionella in the reopening after a period of dormancy and suggests taking steps to reduce the risk.

Treatment actions recommended in the PAHO guidelines include:

  • Drain hot-water tanks, remove sediment and scale (vinegar or other weak acids) and disinfect with 20 ppm chlorine solution;
  • Remove all showerheads and faucet aerators, remove scale (vinegar), clean and disinfect in 0.01% chlorine solution;
  • Shock chlorinate the water supply system Hot and Cold with 20 ppm free residual chlorine in furthest point for 1-2 hrs. and flush all taps until a distinct odor of chlorine is evident;
  • Ensure continuous chlorination (sodium hypochlorite) of at least 0.5 mg / l free residual (in hospitals - and other health care facilities) in the furthest point of supply. In the case of past Legionella infection in hospital or many dead ends in the water system, a 1.0 mg / l residual chlorine is advisable. On-line chlorinators will be required to maintain 0.5-1.0 mg / l residual chlorine.

There are also indications for hot tubs:

  • Remove slime and biofilm from piping by pressure-prop or super-chlorinating weekly and repeat weekly;
  • Maintain a free residual chlorine of 2.0 - 4.0 ppm and check morning, noon and evening.

Shown as an example on slide 9 of the PAHO guidelines, the MIOX system generates mixed oxidant chemistry using three common ingredients: water, salt and power. Disinfectant is produced on site, on demand, allowing it to be applied and dosed according to the specific needs of the application.  The on-site generator produces chlorine solution when salt and water is passed through an electrolytic cell, converting chloride ions present in the solution to mixed oxidant solution. The chlorine-based solution has all the oxidant power of sodium hypochlorite with additional benefits including biofilm removal, which harbors Legionella. The advanced oxidant solution can be effective in preventing a Legionellosis outbreak as we bring more buildings online after many weeks and months of dormancy.

In Europe, several countries are writing guidelines similar to those released by PAHO. On 4 June, for example, the Italian Institute of Health published the "Indications for swimming pools in relation to the spread of the SARS-CoV-2 virus" (report 37/2020). Similar to the PAHO guidelines, the IIH recommends keeping a quantity of continuous free active chlorine in the pool with a value between 1 and 1.5 mg / L. It also indicates the need to sanitize surfaces, including those of ventilation and air conditioning systems and indoor environments. Treatments recommended for the control of Legionella include thermal shock treatment or shock hyperchlorination with sodium hypochlorite. 

As the world slowly wakes up after the 2020 shutdown, world health authorities and local communities are sure to continue issuing guidelines and recommendations to prevent outbreaks of Legionellosis caused by dormant water systems. The last thing we need as we tentatively resume a semblance of normalcy is yet another global crisis.