ANALYSIS OF LEGIONELLA-PNEUMOPHILA STRAINS ASSOCIATED WITH NOSOCOMIALPNEUMONIA IN A NEONATAL INTENSIVE-CARE UNIT

A premature child received continuous mechanical ventilation in a neon atal intensive care unit. On day 10 of his life he developed pneumonia due to Legionella pneumophila serogroup 1, monoclonal subtype Belling ham. The strain was cultured from a tracheal secretion taken on day 10 and detected by immunofluorescence using monoclonal antibodies on day s 10, 12 and 17. Legionella pneumophila serogroups 1 and 6 (10(2)- 4 x 10(4) cfu/l) were cultured from both central and peripheral hot water systems. Monoclonal antibody testing, macrorestriction analysis of th e genomic DNA using pulse-field electrophoresis, and electrophoretic a lloenzyme typing showed the isolate from the child to be identical to the serogroup 1 strains from the hot water system. Four unrelated Legi onella strains of the same monoclonal subgroup Bellingham were studied for comparison. Legionellae were also isolated from two other incubat ors, but no clinical or microbiological indications of legionellosis w ere found in the neonates hospitalised there. Serogroup 1 strains isol ated from the patient and from the hot water system and serogroup 6 is olates from the hot water supply were able to multiply in cultured Aca nthamoeba castellanii cells and in guinea pigs. The serogroup 6 strain , although prevalent in the incubators, was not found in any of the cl inical specimens by either culture or immunofluorescence.