LEGIONELLA - World Health Organization

Legionnaires’ disease is often initially characterized by anorexia, malaise and lethargy;
also, patients may develop a mild and unproductive cough. About half of patients develop
pus-forming sputum, and about one third develop blood-streaked sputum or cough up blood
(haemoptysis). Chest pain, whether pleuritic (i.e. involving infection of the lung lining) or
non-pleuritic, is prominent in about 30% of patients, and may be mistaken for blood clots
in the lungs when associated with haemoptysis. Gastrointestinal symptoms are prominent,
with up to half of patients having watery diarrhoea, and 10–30% suffering nausea, vomiting
and abdominal pains. Fever is present in almost all cases, and fever associated with chills usually
develops within the first day (see references for Table 1.1).
Almost half of patients suffer from disorders related to the nervous system, such as confusion,
delirium, depression, disorientation and hallucinations. These disorders may occur in the first
week of the disease. Physical examination may reveal fine or coarse tremors of the extremities,
hyperactive reflexes, absence of deep tendon reflexes, and signs of cerebral dysfunction. The
clinical syndrome may be more subtle in immunocompromised patients.
Radiographic changes
The radiographic pattern of Legionnaires’ disease is indistinguishable from that seen in other
causes of pneumonia (Mülazimoglu & Yu, 2001). Radiological changes are visible from the third
day after disease onset, usually beginning as an accumulation of fluid in part of the lung, which
can progress to the other lobes, forming a mass or nodule. Diffuse accumulation of fluid
occurs in the lungs of about one quarter of patients. Chest X-rays of immunocompromised
patients receiving corticosteroids may show clearly defined areas of opacity around lung edges,
which may be mistaken for pulmonary infarction. Abscesses can develop in immunosuppressed
patients and, in rare cases, abscesses may penetrate the pleural space, causing pus formation
(empyema) or a bronchopleural fistula (a hole between the bronchus and lung lining, allowing
air to leak). Lung cavitation may occur up to 14 days after initial disease onset, even after appropriate
antibiotic therapy and apparent clinical response. Pleural effusion (the collection of fluid inside
the chest cavity around the lung) is reported in one third of legionellosis cases, and may
occasionally precede the radiographical appearance of fluid accumulation within the lung.
Chest X-rays show progression of fluid accumulation, despite appropriate antibiotic therapy,
in about 30% of cases; however, this does not necessarily indicate a progressive disease (Domingo
et al., 1991). Instead, the spread indicates failure of treatment in association with simultaneous
clinical deterioration.
Abnormalities may persist on X-ray for an unusually long time, even after the patient shows
substantial clinical improvement; clearance rates of 60% at 12 weeks have been reported
(Macfarlane et al., 1984; Stout & Yu, 1997; Yu, 2002).
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS