LEGIONELLA - World Health Organization

Box 9.1 Definition of disease surveillance
Surveillance has been defined as:
… the ongoing systematic collection, analysis, and interpretation of health data, essential
to the planning, implementation, and evaluation of public health practice, closely integrated
with the timely dissemination of these data to those who need to know. The final link in
the surveillance chain is the application of these data to prevention and control. A disease
surveillance system includes a functional capacity for data collection, analysis, and
dissemination linked to public health programmes.
Source: Adapted from CDC (1996)
9.1.1 Standardized case definitions
Combined microbiological and epidemiological case definitions are used for surveillance of
legionellosis. Classifications are shown in Box 9.2.
Box 9.2 Case classifications for legionellosis
Depending on the diagnostic method used and the result, cases are classified
microbiologically as either confirmed or presumptive.
Based on the patient’s clinical history, cases are classified as one of the following:
• Legionnaires’ disease (relevant pneumonic illness and microbiological evidence of infection)
• Pontiac fever or similar illness (relevant non-pneumonic illness and microbiological
evidence of infection)
• asymptomatic Legionella infection (no illness compatible with microbiological result)
• Legionella infection (microbiological evidence of infection but symptoms not known)
• suspected legionellosis (relevant pneumonic or non-pneumonic illness but no
supporting microbiological evidence).
9.1.2 Defined datasets
One of the most important pieces of information in the dataset for surveillance of Legionnaires’
disease is the history of exposure. The incubation period for legionellosis is normally between
two and ten days (see Chapter 1). Thus, whenever possible, an exposure history for two weeks
before the onset of illness should be obtained from the patient (or partner, close relative, friend,
etc.) to provide a focus for further investigations. A home or work diary and street maps are
useful memory aids for this exercise. An example of a two-week exposure history form is given
in Appendix 2.
0 LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS