The present invention involves extracting from Legionella bacteria, particularly L. pneumophila bacteria, an essentially protein-free O-polysaccharide or carbohydrate antigen, coupling this antigen to an activated chromatographic column through a protein spacer molecule which is first conjugated to the antigen, utilizing the column thus prepared for the affinity purification of raw polyvalent antibodies to the same Legionella bacterium from which the O-polysaccharide or carbohydrate antigen was separated—thereby obtaining antigen-specific antibodies which are useful for the rapid detection of the corresponding Legionella bacterium or its antibody in human bodily fluids such as urine, sputum, blood and the like or in environmental samples suspected of harboring the Legionella bacterium.