Legionnaires’ disease: person to person transmission

According to the UK’s NHS healthcare system, Legionnaires disease cannot actually spread from one person to another. Instead it is caused by inhaling droplets of water that have been contaminated with Legionella bacteria.

One of the legionnaire’s disease that occurred in Portugal has led the medical community to questions whether person to person transmission may be possible after all.

This case occurred in November 2014, when a man was found to be one cluster of people suffering from Legionnaires diseases.

Causes and common sources of Infection

Legionella found naturally in fresh water. When people are exposed to the bacterium, it can cause illness. This bacterium grows best in warm water, like the kind found in:

  • Hot tubs
  • Cooling towers (air-conditioning units)
  • Hot water tanks
  • Large plumbing systems
  • Decorative fountains

Exposure and Transmission

People are exposed to Legionella when they breathe in small droplets of water in the air containing the legionella bacteria. One example might be from breathing in droplets sprayed from a hot tub that has not been properly cleaned and disinfected.

Legionella can be spread by drinking water, which has gone down the wrong pipe. People at increased risk of aspiration include those with swallowing difficulties.

In general, Legionella does not spread from one person to another. However, this may be possible in VERY rare cases.

Most people exposed to the bacteria do not get the disease. If you think you have been exposed to the bacteria, talk to your doctor or local health department.

The probability of Legionella infection can be best reduced by good engineering practices in the operation and maintenance of air and water handling systems. Cooling towers and evaporative condensers should be inspected and thoroughly cleaned annually.

Rusted parts should be replaced. These measures will not only control the growth of bacteria, but will also maintain operating efficiency.

Cooling water should be treated constantly. Ideally, an automatic water treatment system should be used that continuously controls the quality of the circulating water. Hot water tanks, which also might provide ideal conditions for the growth of Legionella, should be cleaned regularly.

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