Legionella IFA test
|Lab name||Legionella Reference Laboratory|
|Lab location||Kenepuru Science Centre, Porirua|
|Test name||Legionella IFA test|
|Requested for surveillance||yes|
|Routine turnaround time||5 working days|
|Culture requirements||Paired serum samples (at least 500 μL samples) – initial taken within seven day of onset of symptoms (acute serum), second taken at least 3 weeks after the initial sample (convalescent serum)|
|Pre-transport requirements||Send serum samples immediately. If shipping is delayed for more than 48 hours, store frozen at -20°C. Avoid repeated freezing and thawing of serum, as this will decrease the antibody titre.|
|Transport requirements||Send at 5 ± 3°C or -20°C within 24 hours.|
|Unacceptable sample types||Haemolysed serum; single serum samples|
|How results reported||Positive or negative for the detection of anti-legionella antibodies|
The indirect immunofluorescent assay (IFA) for Legionella is used for the detection of anti-legionella antibodies in human serum. It is a "sandwich" immunoflorescent technique that uses a two-stage reaction procedure.
In the first stage, Legionella whole-cell antigens are fixed to a microscope slide and overlaid with diluted human serum. Following incubation & washing steps, the human serum-antigen complex is overlaid with a fluorescein-labelled anti-human whole globulin.
The Legionella antigen is rendered fluorescent if anti-Legionella antibodies have attached. The amount of fluorescence is directly proportional to the amount of human antibody attached to the antigen.
The antibody titre results reported are the inverse of the highest serum dilution where fluorescence is detected. To detect an increase in antibody titre, both acute and convalescent sera must be tested in parallel.
Single sample testing is not considered a valid test.
Information sheet on Legionella and Legionellosis [PDF, 137 KB]