Legionella pneumophila mip gene sequencing to investigate a cluster of pneumonia cases.

Aims: To use fluorescent antibody (FA) and PCR studies on fixed lung tissue to investigate whether Legionella pneumophila was the cause of pneumonia in a cluster of three haematology patients.

Methods: Cut sections of paraffin blocks of lung tissue were examined by direct FA (DFA) using fluorescently labelled antibody to serogroup 1 and Pontiac strains of L. pneumophila. In addition, a single tube 'hanging drop' nested PCR targeting the mip gene of Legionella was performed on DNA extracted from the lung sections. Products were sequenced using dye terminator chemistry.

Results: Numerous fluorescing bacteria were seen on staining with both antibodies in lung tissue from two of the patients. Identical L. pneumophila mip gene sequences were amplified from both DFA-positive lung sections. Two differing L. pneumophila mip sequences were obtained on three separate occasions from the tissue sections from the third patient negative by DFA. These sequences differed slightly from those obtained from the two DFA positive lung tissues.

Conclusions: There is good epidemiological evidence to link the first two cases who had been treated in the same ward prior to development of fever within two days of each other. The significance of results is controversial for the third patient.