Legionella and its favorite habitat!

 

Three years ago, BCI received an emergency call from a ship cleaning company regarding a vessel scheduled to dock at the Port of New Orleans. The ship had been intermittently battling Legionella contamination for approximately three to six months. Initially perceived as an on-and-off issue, our investigation revealed a more systemic problem. During the ship's last dry dock period, the 150,000-gallon potable water tanks were not properly disinfected upon recommissioning, leading to the outbreak.

Within 48 hours, we took decisive action by cleaning and purging the water tanks and shocking all potable water lines to eradicate the bacteria. We replaced all water fixtures on board the tanker to ensure no residual contamination remained. To prevent future occurrences, we left behind test kits and a sufficient supply of chlorine to last the ship's operational life. Additionally, we provided a comprehensive guidance manual to help maintain conditions inhospitable to Legionella growth.

Key Legionella Facts on Motor Vessels:

• Reported Issues: There have been over 200 reported cases of Legionnaires' disease on ships in the past three decades, with one notable case on a cruise ship leading to 50 infected crew members and one fatality.
• Ideal Conditions for Legionella: Legionella thrives in water systems where temperatures range between 20-45°C (68-113°F), commonly found in ship water supplies. Like that in improperly managed or maintained water tanks, stagnant water provides an ideal breeding ground.
• Prevention Measures: Proper maintenance includes regular disinfection of water systems, temperature control, and avoiding dead legs in plumbing where water can stagnate. Regular flushing of systems and the use of anti-Legionella valves can also be effective in preventing bacterial growth.

The perfect environment for Legionella involves water temperatures that are not too hot or too cold, adequate nutrients from system materials or organic matter, and low-flow areas where water can stagnate. While these conditions can vary, this scenario represents a general consensus on what facilitates Legionella proliferation.

#Legionella on cruise ships

#waterborne diseases on ships

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Legionella bacteria thrive under specific conditions, which include:

1. Warm Water Temperatures:

Optimal growth occurs between 77°F (25°C) and 113°F (45°C).

Growth is inhibited below 68°F (20°C) and above 122°F (50°C), with temperatures above 140°F (60°C) killing the bacteria.

2. Stagnant Water:

Stagnation allows biofilm formation, which provides a protective environment for Legionella to multiply. Biofilms also shield the bacteria from disinfectants.

3. Low Oxygen or Aerobic Conditions:

While Legionella requires oxygen to grow (it is aerobic), it can thrive in environments with poor circulation where oxygen exchange is limited.

4. Nutrient-Rich Environments:

The presence of organic matter, scale, and sediment provides nutrients for the bacteria and other microorganisms that can support biofilm formation.

5. Presence of Amoebae:

Legionella can multiply within amoebae, which serve as hosts, enhancing their survival and spread.

6. pH Levels:

Prefers slightly acidic to neutral pH, generally between 5.0 and 8.5.

7. Lack of Disinfection:

Inadequate levels of chlorine or other biocides in water systems allow the bacteria to proliferate.

Common Locations Favoring Legionella Growth:

• Cooling towers and evaporative condensers.
• Hot water systems, such as water heaters, showers, and faucets.
• Spa pools, whirlpools, and decorative fountains.
• Plumbing systems with stagnant sections or "dead legs."
• Industrial equipment that uses water, like humidifiers.

To control Legionella, it's essential to maintain proper water temperature, circulation, and disinfection, and to minimize areas where water can stagnate.