Health Tips

Legionnaires' disease

Legionnaires' disease (LD) is an infectious disease caused by Legionella species, with L. penumophila being the most pathogenic. It was first recognised in 1976, when an outbreak of pneumonia took place during an American Legion convention.

Legionella lives in water and can be found in water tanks, hot and cold water systems, humidifiers in air conditioning systems, cooling towers and water fountains. Warm water
(25°C - 42°C) enhances its growth. Disinfection and proper maintenance of the water systems are the most effective ways to prevent the disease.

LD accounts for 2-9% of all community-acquired pneumonia. In HK, there is an increasing trend speculated with 11 to 37 cases reported each year from 2005 to 2011.

People may get infected if they breathe in contaminated droplets or mist generated by artificial water systems. Infection is not disseminated through person-to-person contact.

The incubation period of LD is about 2-10 days. Infected persons usually display a fever, dry cough, shortness of breath, tiredness and muscle pain. Some people also get abdominal pain, nausea, vomiting and diarrhoea. In severe cases, organ failure and even death may result. Older people above 50 and those with chronic lung diseases, weakened immunity or who smoke are more susceptible to the infection.

Macrolides (e.g. azithromycin) and respiratory fluroquinolones (e.g. levofloxacin or moxifloxacin) are the antibiotics of choice for LD. Fluoroquinolones are preferred for transplant patients to avoid drug interaction with the immunosuppressants. The usual treatment duration is 7-14 days, but this may extend to 21 days for immunosuppressed patients or those with severe diseases.

Currently, there is no vaccine available for LD. For preventive measures, people should observe personal hygiene, avoid smoking and excessive drinking, maintain domestic water filters properly and clean their water tanks regularly. People with weakened immunity are advised to use distilled or boiled water for drinking, brushing their teeth and mouth rinsing, and avoid using humidifiers.

Source: Drug Education Resource Centre, The Society of Hospital Pharmacists of Hong Kong