What is Legionnaire’s disease (Legionella pneumonia; Pontiac fever)

An outbreak of serious pulmonary infections among people attending a convention of the American Legion in Philadelphia during the US Bicentennial celebration in July 1976 prompted the description of Legionnaire’s disease and its causative organism, Legionella pneumophila.
A nonpneumonic variant caused by the same species is called Pontiac fever, named for an outbreak of the described disease in Pontiac, Michigan, in 1968.
The bacterium can cause a broad spectrum of disease from mild cough and fever to a serious pneumonia.

Statistics on Legionnaire’s disease (Legionella pneumonia; Pontiac fever)

In the US since the initial identification of 235 cases in 1976, Legionnaire’s disease has become recognized as the most common cause of atypical pneumonia in hospitalized patients. It is the second most common cause of community-acquired bacterial pneumonia. Legionnaire’s disease is reportable in the US. The Centers for Disease Control and Prevention in the US (CDC) received reports of 1241 cases in 1995, indicating an incidence of 0.48 cases per 100,000 people. This represents passive disease surveillance. More active surveillance methods estimate that upwards of 20,000 cases occur annually in the US.
On an international scale outbreaks have been recognized throughout North America, Africa, Australia, Europe, and South America.
Legionnaire’s disease has a 25% mortality rate. Having said this, this figure should be interpreted cautiously because of possible underreporting of linked diseases.
Rhabdomyolysis and renal failure may be seen in this disease.
Men are affected more frequently than women. The average age for patients with Legionnaire’s disease is 52.7 years, with increasing incidence until age 79. Older patients have higher mortality rates.

Risk Factors for Legionnaire’s disease (Legionella pneumonia; Pontiac fever)

Legionnaire’s’ disease is most often contracted by inhaling mist from water sources such as whirlpool baths, showers, and cooling towers which are contaminated with Legionella pnuemophila bacteria, or other bacteria in the family Legionellaceae.

Progression of Legionnaire’s disease (Legionella pneumonia; Pontiac fever)

Legionnaire’s’ has an incubation period of between two and 10 days.
Initial symptoms of are similar to those of flu: headache, musclepain, and a general feeling of being unwell.
These symptoms are followed by high fever and shaking chills. Nausea, vomiting, and diarrhoea may occur.
On the second or third day, dry coughing begins and chest pain might occur. There may also be difficulty breathing.
Mental changes, such as confusion, disorientation, hallucination and loss of memory, can occur to an extent that seems out of proportion to the seriousness of fever.
Some patients may develop pneumonia . This could affect both lungs and lead to hospitalisation if severe.

How is Legionnaire’s disease (Legionella pneumonia; Pontiac fever) Diagnosed?

  • Listening to the chest with a stethoscope reveals fine crackles.
  • Sputum direct fluorescent antibody staining shows Legionella.
  • The causative bacterium may be cultured from the airway.
  • Urine tests for the bacteria (urine antigen test) may prove positive.
  • Chest x-ray indicates pneumonia.

Prognosis of Legionnaire’s disease (Legionella pneumonia; Pontiac fever)

The overall death rate for those with pneumonia is about 15%, and the death rate increases in those with underlying diseases. The mortality for patients who develop Legionnaire’s disease while hospitalized is close to 50%, especially when antibiotics are started late.

How is Legionnaire’s disease (Legionella pneumonia; Pontiac fever) Treated?

The goal of treatment is to eradicate the infection with antibiotics. Treatment is started as soon as Legionnaire’s disease is suspected, without waiting for confirmation from culture results.
The antibiotic commonly used is quinolone (ciprofloxacin, levofloxacin, moxifloxacin, or gatifloxacin) or a macrolide (azithromycin, clarithromycin, or erythromycin).
Supportive treatment includes hospitalization for fluid and electrolyte replacement and oxygen administration by mask or by mechanical ventilation, that is if the respiratory system of the patient has become severly affected and requires assistance.

Legionnaire’s disease (Legionella pneumonia; Pontiac fever) References

  1. Center for Disease Control and Prevention: Summary of notifiable diseases, United States 1995. MMWR Morb Mortal Wkly Rep 1996 Oct 25; 44(53): 1-87.
  2. MEDLINE Plus.
  3. eMEDICINE.
  4. BBC Website.[6] Falco V, de Sevilla TF, Alegre J, et al: Legionella pneumophila. A cause of severe community-acquired pneumonia. Chest 1991; 100: 1007-1011[Medline].
  5. Cunna B: Legionnaire’s disease – Case studies in infectious disease. Emerg Med 1992; 24: 227-234.