A family cluster of Legionella pneumophila infections.

Three members of one single family of 4, the father, a son and a daughter, showed seroconversion against Legionella pneumophila serogroup 1 (Lp SG1). The son had a severe pneumonia, whereas the father and the daughter did not develop any other illness than mild and transient fever. A fourth member, the mother, remained seronegative. Lp SG1 was detected by a direct immunofluorescence test in water samples from the shower at home, in tap water in the family's butcher shop, and in condensation water from the ventilator of refrigerator cells in the shop. Two different sources of infection appear to have occurred: showering at home and an aerosol of contaminated condensation water. Reports of more than one case of legionella infection within a family seem to be extremely rare and have not been found in the literature.