A closer look at Legionnaires' Disease

A total of 20 nosocomial infection cases of Legionnaires’ Disease (LD) were recorded in the Hospital Authority (HA) from 2011 to 2023. Although most cases were without epidemiological linkage and the number of cases remains at a low level, the HA still stays vigilant. The expert panel has reviewed the prevailing measures within hospitals and has recommended to strengthen preventive and control measures targeting various aqueous environments, including altering the conditions necessary for the proliferation of Legionella bacteria in water tanks, hot and cold water systems, to reduce the spread of LD.

Infectious agent: Legionella, named after an outbreak of chest infection occurring in a Legion Convention in the United States in 1976

Risk factors: Males, people aged 50 or above, smokers, alcoholics, persons with weakened immunity, especially those with chronic illnesses (such as cancer, diabetes mellitus, chronic lung or kidney diseases), and those taking corticosteroids or drugs that suppress body immunity

Mode of transmission: Legionella bacteria are found in various environmental settings and grow well in warm water (20°C to 45°C). They can be found in aqueous environments such as water tanks, hot and cold water systems, cooling towers, whirlpools and spas, water fountains and home apparatus for breathing support. Generally speaking, the bacteria are not transmitted between humans through direct contact. Rather, patients are infected mainly when they breathe in contaminated droplets (aerosols) and mist generated by artificial water systems or when handling garden soil, compost and potting mixes

Symptoms: fever, cough, shortness of breath, tiredness, headache, muscle pain, and may have abdominal pain and diarrhea. In severe cases, neurological symptoms (e.g. confusion) and respiratory failure may appear and some may cause death. Average mortality rate for sporadic cases is 10 to 15%, the mortality rate is higher in patients without immediate treatment

Incubation period: 2 to 10 days

Treatment and prevention: Antibiotics are the mainstay of treatment, no vaccine is available for LD