—from Epidemiological Bulletin, Vol. 22 No. 1, March 2001—

Case Definition:
Legionellosis

Rationale for Surveillance
Legionnaires’ disease is a disease with epidemic potential and high case-fatality. Surveillance is important in order to detect epidemics and to institute appropriate investigations and control measures. In addition, the surveillance of sporadic disease may provide clues as regards source of disease and prevention.

Recommended case definition
Clinical description
An illness characterized by an acute lower respiratory infection with focal signs of pneumonia on clinical examination and/or radiological evidence of pneumonia

Laboratory criteria for diagnosis
Presumptive: one or more of the following:
· Detection of specific legionella antigen in respiratory secretions or urine.
· Direct fluorescent antibody (DFA) staining of the organism in respiratory secretions or lung tissue, using evaluated monoclonal reagents.
· A fourfold or greater rise in specific serum antibody titer to legionella species other than Legionella pneumophila serogroup 1, using a locally validated serological test.

Confirmative: one or more of the following:
· Isolation of Legionella from respiratory secretions, lung tissue, pleural fluid, or blood.
· A fourfold or greater rise in specific serum antibody titer to L. pneumophila serogroup 1 by indirect immunofluorescence antibody test or microagglutination.
· Demonstration of L. pneumophila serogroup 1 antigen in urine by radioimmunoassay.

Case classification
Suspected: Not applicable.

Probable: A case compatible with the clinical description, with presumptive laboratory results.

Confirmed: A case compatible with the clinical description, with confirmatory laboratory results.

Recommended types of surveillance
Immediate reporting of case-based data from periphery to intermediate and central levels.

The identification of cases should prompt immediate investigation for risk factors and other cases. For a rapid response, active case finding is preferred.

International: Since travel and stays in hotels are important risk factors, effective international surveillance is essential to identify and control the point source of infections.

Legionella infection is usually diagnosed after the patient’s return to the country of residence and is therefore likely to be considered as a sporadic, single case.

A surveillance scheme such as the European Working Group for Legionella Infections* (see special aspects) allows for the detection of clusters of cases (2 or more cases) with the same source of transmission, as case notifications from different European countries are collected in the same database.

Recommended minimum data elements
Case-based data for investigation and reporting:
Unique identifier, name, age, sex, geographical information, date of onset, outcome.

Underlying risk factors (e.g., immunocompromized patient, AIDS).

Exposure risk factors (hospitalizations, hotels, or other accommodation and travel history during the 2 weeks before the onset).

Laboratory data (specimen type, date collected, Legionella spp. isolated).

Recommended data analyses, presentation, reports
Review data regularly to look for clusters of cases in time, place or person (this should be undertaken at all levels).
Incidence of infection by month, geographical area, age group, risk factors, exposure factors.

Principal uses of data for decision-making
· Detect clusters/outbreaks
· Identify high risk areas and exposures
· Monitor impact of environmental control measures

Special aspects
There are 2 currently recognized distinct clinicoepidemiological manifestations of legionellosis:

· “Legionnaires’ disease” (pneumonic form) and
· “Pontiac fever”(non-pneumonic Legionnaires’ disease).

Both are characterized initially by anorexia, vomiting, myalgia and headache, followed within a day by rising fevers and chills.

In the pneumonic form, non-productive cough, abdominal pain/diarrhea, confusion/delirium are common. It is not possible, clinically, to distinguish Legionella pneumonia from other pneumonias; suspicion should be raised in any pneumonia connected with epidemiological information (e.g., recent travelling, hospitalization, gatherings, immunosuppression). In addition, age (>50), sex (Male), smoking, alcohol consumption have been shown to be risk factors.

Pontiac fever is not associated with pneumonia. It is thought to represent a reaction to inhaled antigen, rather than to bacteria.

The reservoir of Legionella spp. is probably primarily aqueous (e.g., hot water systems, air-conditioning, cooling towers and evaporative condensers). Environmental surveillance for Legionella in water sources can be undertaken usually as part of registration and licensing procedures. In any event, environmental surveillance should be undertaken for known sources of outbreaks, to ensure that the organism is eradicated.

*European Working Group on Legionella Infections PHLS Communicable Disease Surveillance Centre 61 Colindale Avenue, London NW9 SEQ Tel: (44) 181 200 6868 E-mail: respedsc@PHIS.co.uk Fax: (44) 181 200 7868

Source: "WHO Recommended Surveillance Standards, Second edition, October 1999", WHO/CDS/CSR/ISR/99.2

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Epidemiological Bulletin , Vol. 22 No. 1, March 2001