Legionnaires' disease is caused by Legionella bacteria, which can cause pneumonia. The bacteria infects the lungs by entering respiratory cells and inhibiting normal acidification, allowing proliferation. This causes inflammation and cell death, recruiting neutrophils and depositing fibrin in the lungs. L. pneumophila is the most common cause, found in water sources. It was first identified after an outbreak in 1976 infected 182 people and killed 29. Symptoms include fever, cough, and muscle aches. Diagnosis involves urine or sputum tests. Treatment uses antibiotics like fluoroquinolones or azithromycin. Prevention focuses on proper water system maintenance to eliminate bacterial growth.

1. Legionnaires’ disease
By Sonia Kaur

2. What is Legionnaires’ disease and how is
it caused?
Legionnaires’ disease is a condition caused by Legionella bacteria causing a fatal type of pneumonia, which is contracted by
airborne water droplets. It is the common cause for community-acquired and hospital-acquired pneumonia
In the lower respiratory tract, bacteria binds to the respiratory epithelial cells and alveolar macrophages, after cell entry.
This causes inflammation because Legionella is a facultative intercellular parasite which can multiply in macrophages. Once
cell entry has occurred, phagosome-lysosome fusion is inhibited, preventing normal acidification of phagolysosome. This
promotes proliferation of Legionella, releasing new microbes to infect other cells.
Due to bacterial growth, the complement system is activated and there is production of chemotactic factors because of
alveolar macrophage death, causing an influx of neutrophils. Leaky capillaries allow deposition of fibrin in the alveoli and
this causes severe pneumonia due destruction of air spaces and effected respiratory function.

3. Legionella
The family Legionellaceae has more than 50 species and 70 serogroups.
L.pneumophila is the most common serogroup. Serogroups 1, 4, and 6 identified
as the causes of human disease. Serogroup 1 is thought to be responsible for
80% of the reported cases.
L. pneumophila is a non-marine bacteria that grows inside other organisms like
protozoans. It can also be found in large bodies of fresh water like lakes.
Gram-negative aerobic pleomorphic organism, either rod or coccobacilli.
L. pneumophila appears as a small to short rod with a length of 3 to 5 μm. When
cultured, it appears as a long filamentous bacillus with a length of 10-25 μm

4. Back ground history
The Legionella bacterium was first identified in 1976 in Philadelphia, US. The infection was believed to be caused by contaminated
water in the air conditioning system.
Patients developed flu like symptoms to multi-organ failure. 182 were believed to be infected, and 29 died. The main cause of
mortality is respiratory failure.
The most recent outbreak was in 2015 in multiple U.S. states, which traced back to water supplies. Due to correct identification of
the source of contamination, the outbreak was controlled in a timely manner. Testing and decontamination of the local water
sources was conducted.

5. Symptoms
Exposure and symptom onset is 2 to 10 days but may be up to 20. Those exposed to the infection, between 0.1 to 5%
develop the disease, 0.4 to 14% are hospitalised.
Symptoms include:
◦ Fever due to infection because of pathogen colonisation.
◦ Cough producing sputum. 1/3 of patients exposed experience coughing up blood.
◦ Muscle aches
◦ Headaches
◦ Loss of appetite.
◦ Chest pain.
◦ Diarrhoea.
◦ Neurological symptoms.

6. Diagnosis
Early diagnosis allows correct treatment to be given which reduces mortality rates. Diagnosis can include urine
antibody test and sputum culture.
◦ Urine antibody test is quick with sensitivity of more than 85% and specificity of more than 99%. However, only
tests for L.pneumophila which is the most common cause of infection, avoiding diagnosis for other species like
L. micdadei, L. bozemanii, L. dumoffii, and L. longbeachae.
◦ Sputum culture takes 3-5 days to grow which is time consuming, however it can identify other species that are
present. Sputum sample must be taken before antibiotic administration.

7. Different diagnostic tests
Test Sensitivity (%) Specificity (%)
Culture 20–80 100
Urinary antigen for L.
pneumophila serogroup
1
(Lp1)
70–100 95–100
Polymerase Chain Reaction
(PCR)
2
95–99 >99
Direct Fluorescent Antibody
(DFA) Stain
25–75 >95
Paired serology
3
80–90 >99
Table 1: The different diagnostic test used to identify species of Legionella.
Sensitivity variety depends on the quality of sample and timing.

8. Treatment and prevention
Treatment:
◦ Antibiotics are a method of treatment for Legionnaires’ disease and the type used include fluoroquinolones, macrolides, and rifampin. Either
Levofloxacin 750 mg, one tablet for seven to ten days, or Azithromycin, 1 gm on day one followed by 500 mg one tablet once a day for seven to
10 days, are advised.
◦ Antibiotics by mouth being intolerable by some patients due to gastrointestinal symptoms, parenteral therapy is advised.
◦ Some patients require ventilation due to chest pain and poor respiratory output. As well as supportive nutrition due to the loss of appetite.
Prevention:
◦ Hospitals across the country frequently test water supplies. Proper decontamination of the water supply is recommended. This is by heating
water to 70 C to 80 C, with flushing of distal sites. As well as using UV light to kill legionellae.
◦ Copper-silver ionization units are effective at preventing legionellae, providing protection.
◦ Hyperchlorination of water is not effective because legionellae are chlorine resistant, and chlorine decomposes at the higher temperatures.
◦ To prevent Legionella growth in water systems is ideal to prevent infection. In order to do this, timely identification and reporting of cases allows
public health officials to act accordingly. This allows source of infection to be identified and this prevents outbreaks, by linking it to the cause.

9. Recap
◦ Legionella pneumonia is a serious respiratory tract infection mainly affecting the elderly.
◦ If the diagnosis is missed or treatment is delayed the morbidity and mortality are very high, because the infection is
progressive and can result in multiorgan failure. With effective medication mortality can be reduced.
◦ Experience and knowledge from previous outbreaks reveals that an interprofessional group of healthcare workers is
important to help decrease the morbidity of the infection. This is so that source of the outbreak can be identified
and monitored.
◦ Knowledge must be up to date on the current antibiotics used for the treatment of the infection due to the risk of
antibiotic resistance or patient intolerance.