Introduction

Legionnaires’ disease is a pneumonia with the patients' experiencing non-specific prodromal symptoms including fever, malaise, myalgia, anorexia and headache or a prodrome resembling gastroenteritis, caused by a number of species of the genus Legionella.  It is not common. The organism reproduces in warm water, such as in air conditioning systems. Spread is by aerosol, there is almost no person-to-person transmission. The disease is often acquired in buildings such as hospitals and hotels, but most cases are acquired in the community.  Mortality in 1998 was 11% and there is often some long-term damage to the lungs.

Aetiology of Legionnaires’ disease

The causative organisms, Legionella spp. are widespread in the environment, particularly in water supplies. 

Diagnosis of Legionnaires’ disease

Clinical

There is a broad-spectrum of signs and symptoms of Legionnaires’ disease.

Laboratory diagnosis

• Urinary antigen.
• Serology.
• Direct immunofluorescence for Legionella spp. should be requested if available at the laboratory.
• Sputum Gram stain.
• Sputum culture.
• Blood culture.
• Biochemistry.

Management of Legionnaires’ disease

Treatment initiation should be rapid: delay increases mortality.

Antibiotics are the mainstay of treatment.  The agents used must be able to penetrate into phagocytes, and many agents with good in vitro activity against Legionella spp. have little or no effect in vivo (eg. penicillin, ampicillin, gentamicin).  Legionella spp. are not easily eradicated by host defences and relapse is possible, particularly in the immunocompromised, so extended courses of therapy may be required. The preferred regimens are:

Mild to moderate disease:

• A quinolone such as ciprofloxacin, or a macrolide such as erythromycin, or both agents in combination, for two to three weeks.

Severe disease:

• A macrolide plus rifampicin, for two to three weeks

or

• A quinolone such as ciprofloxacin plus a macrolide.

Prevention of Legionnaires’ disease

Prevention largely consists of public health measures to control the contamination of water supplies, heating water to >58°C and surveillance of water quality.