(Legionnaires' disease, Legionnaires' pneumonia)

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 titre 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 titre to L. pneumophila serogroup 1 by indirect immunofluorescence antibody test or microagglutination

 

Note: Most European countries and others such as the United States now include the detection of L. pneumophila serogroup 1 antigen in urine as a confirmatory test.

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 confirmative 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 cases) with the same source of transmission, as case notifications from different European countries are collected in the same database.

 

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

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., immunocompromised 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/diarrhoea, 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 (M), 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.

CONTACT

Regional Offices:

See Regional Communicable Disease contacts on section "Communicable disease contacts in Regional Offices".

Headquarters: 20 Avenue Appia, CH-1211 Geneva 27, Switzerland

Communicable Diseases Surveillance and Response (CSR)

 

E-mail: tikhomirove@who.ch / outbreak@who.ch
Tel: (41 22) 791 2656/2850/2111
Fax: (41 22) 791 4878/0746 attn CSR