LEGIONELLA - World Health Organization

Long-term effects
If untreated, Legionnaires’ disease usually worsens during the first week and can be fatal. The
most frequent complications are respiratory failure, shock and acute renal and multi-organ failure.
Appropriate early treatment usually results in full recovery; however, long-term pathological
conditions resulting from the disease (sequelae) may occur. Minor problems may include
persistent pulmonary scars and restrictive pulmonary disease in some patients who experience
severe respiratory failure. In severe infections, there are often general secondary symptoms, such
as weakness, poor memory and fatigue, which can last for several months. Other neurological
deficits that can arise from severe infection include residual cerebellar dysfunction (Baker,
Farrell & Hutchinson, 1981), retrograde amnesia, and cerebellar signs and symptoms (Edelstein
& Meyer, 1984), although retrograde amnesia is the only one of these deficits to be noted
relatively frequently.
Incubation period
The incubation period is the time interval between initial exposure to infection and the appearance
of the first symptom or sign of disease. The average incubation period of Legionnaires’ disease
is 2–10 days (WHO, 2004), although it may extend to even longer than 10 days. An epidemiological
study of a major outbreak of Legionnaires’ disease associated with a flower show in the Netherlands
found that 16% of cases had incubation times longer than 10 days, with the average being
7 days (Den Boer et al., 2002; Lettinga et al., 2002).
Diagnosis and treatment
Attempts to establish predictive scores that identify Legionella pneumonia in individual patients
have been unsuccessful. Although several clinical signs and symptoms have been described as
characteristic of legionellosis (as outlined above), there is a considerable overlap of symptoms for
Legionnaires’ disease and Legionella pneumonia. This overlap makes it difficult to develop a
checklist of characteristics for diagnosing individual patients infected with Legionella (Gupta,
Imperiale & Sarosi, 2001; Mülazimoglu & Yu, 2001; Roig & Rello, 2003).
In targeting antibiotic therapy, it is best not to rely on diagnosis of a syndrome if there is no
microbiological diagnosis. Generally, the recommended approach for all patients with pneumonia
acquired in the community is an initial trial antimicrobial treatment, based on assessment of
pneumonia severity and host-related risk factors (see Section 1.3).
Causative agents
Legionnaires’ disease is usually caused by L. pneumophila, but in some cases one or more additional
organisms may also be involved, resulting in a mixed (polymicrobial) infection. Culture of
these co-infectors has revealed a wide spectrum of organisms, including aerobic bacteria (those
that require free or dissolved oxygen, such as Mycobacterium tuberculosis), anaerobic bacteria
(those from environments without such oxygen), viruses and fungi (Roig & Rello, 2003).
Section 1.4 discusses the causative agents in more detail.
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS