Q&A about legionellosis

Legionellosis is a respiratory infectious disease caused by the Legionella bacteria. So far, there have been more than 50 species and at least 70 serotypes of Legionella, among which Legionella pneumophila (Lp) causes more than 90 percent of legionellosis. Legionella pneumophila has at least 15 serotypes. Serotype Lp1 is the major cause of legionellosis in humans. Serotypes Lp1, Lp3, Lp5, Lp6 and Lp9 have been found in environmental waters in China.

 

Legionella bacteria are found naturally in natural waterbodies such as lakes and rivers. The most likely source of Legionellosis is artificial water supply systems that provide an environment for Legionella to grow and spread.

 

The most common transmission method of Legionella is inhalation of contaminated aerosols produced in conjunction with water sprays, jets or mists of contaminated water sources. Infection can also occur by aspiration of contaminated water or ice, particularly by susceptible hospital patients, and by exposure of babies during water births. 

 

The sources of aerosols related to spread of legionella bacteria include air conditioning cooling towers, hot and cold-water supply systems, hot tubs, decorative fountains and water features and cycling water systems. To date, there has been no reported direct human-to-human transmissions.

 

People prone to the disease include:

 

People at or above 50 years of age  

Current or former smokers

People with a chronic lung disease (such as chronic obstructive pulmonary disease or emphysema)

People with weak immune systems or who take drugs that weaken the immune system (such as after a transplant operation or chemotherapy)

People with cancer

People with underlying illnesses such as diabetes, kidney failure, or liver failure

 

What are the epidemic characteristics of legionellosis?

The disease occurs in all seasons, but mostly in summer and autumn. It can be widely found around the world. 

 

Legionellosis is a generic term describing the pneumonic and non-pneumonic forms of infection with Legionella. 

 

The non-pneumonic form (Pontiac disease)

 

The non-pneumonic form (Pontiac disease) is an acute, self-limiting influenza-like illness usually lasting two to five days. The incubation period is from 5 to 66 hours. The main symptoms are fever, chills, headache, malaise and muscle pain (myalgia). No deaths are associated with this type of infection.

 

The pneumonic form

Legionnaires' disease, in the pneumonic form, has an incubation period of two to 10 days (but a period of up to 16 days has been recorded in some outbreaks). Initially, symptoms are fever, loss of appetite, headache, malaise and lethargy. Some patients may also have muscle pain, diarrhea and confusion. There is also usually an initial mild cough, and as many as 50 percent of patients have phlegm. Blood-streaked phlegm or hemoptysis occurs in about one-third of the patients. Disease severity ranges from a mild cough to a rapidly fatal pneumonia. Death occurs through progressive pneumonia with respiratory failure and/or shock and multi-organ failure.

 

Legionellosis should be diagnosed based on the history of epidemiology, clinical manifestation and laboratory test results. Other indicia are that two weeks before the occurrence of the disease the patient was in contact with a human-made building water system such as an air conditioning cooling tower water, thermal water or a hot and cold piped water system. The patient may also have been to an area experiencing a legionellosis outbreak within the two weeks prior to the occurrence of the disease.

 

Its clinical manifestations include fever, headache, non-drug-induced disorders of consciousness or drowsiness, non-drug-induced diarrhea, shock, acute liver and kidney function injury, and hyponatremia. 

 

The test methods of the laboratory diagnosis for the disease involve etiological examination, serum antibody testing, molecular biological examination and rapid detection of urinary antigens. 

 

To kill or inhibit the growth of bacteria, the preferred drugs are Levofloxacin and Azithromycin. 

 

For patients with mild to moderate Legionella pneumonia, the recommended course of treatment is 10 days, while patients with severe pneumonia, basic diseases and poor immune functions should be treated for three weeks. Patients with combined lung abscesses and severely compromised immune function should undergo longer treatment to prevent recrudescence. 

 

There is no vaccine currently available for Legionnaires' disease.

 

Preventing Legionnaires' disease depends on applying control measures to minimize the growth of Legionella and dissemination of aerosols. These measures include good maintenance of devices, regular cleaning and disinfection and applying other physical (temperature) or chemical measures (biocide) to minimize growth. Some examples are: 

 

The regular maintenance, cleaning and disinfection of cooling towers together with frequent or continuous addition of biocides; 

 

Installation of drift eliminators to reduce dissemination of aerosols from cooling towers; 

 

Maintaining an adequate level of a biocide such as chlorine in a spa pool along with a complete draining and cleaning of the whole system at least weekly;