Evidence

High assurance to link source with cases -----------------------------------------------------------------→ Low assurance

Epidemiological

1) Strong association linking source to cases on a well designed analytical epidemiological study.

2) Strong association linking source to cases from descriptive epidemiological study when analytical study can't be done due to small sample size or resource implications

OR

Association linking source to cases described by analytical study but with flaws in study design/methodology such as small sample size or bias in selecting controls in case control studies.

3) Association linking source to cases with source demonstrated with simple spatial mapping, statistical analysis or from descriptive epidemiology.

4) Association linking source to cases with source suggested by simple spatial mapping or from descriptive epidemiology.

5) Anecdotal case histories with poor traceability of those exposed.

Environmental Investigation

1) Isolation of specific Legionella (sub)species from environmental sample matching clinical sample

AND

Source where risk has not been managed/documented adequately.

2) Isolation of specific Legionella (sub)species from environmental sample matching clinical sample.

3) Isolation of non-specific Legionella from environmental sample

AND

High risk source with documented failure of controls or poorly managed risks.

4) Isolation of non-specific Legionella from environmental sample

OR

Source where controls in place have not been audited or managed.

5) Suspected source is the only possible source

OR

Presence of bio films at a source

OR

Closure of source stopped new case.

Clinical Microbiology

1) Isolation of specific Legionella (sub)species from clinical samples matching environmental specimens.

2) Detection of Legionella as per the confirmed case definition, for most cases, with similar or more detailed isolation from environmental sample (noting that in the case of SG1 this might be found in random environmental samples).

3) Detection of Legionella as per the probable case definition, for most cases.

4) Legionella diagnosis on basis of clinical and radiological evidence alone.

5) Retrospective diagnosis on basis of clinical history alone in whom Legionella may not have been suspected initially.