Two Sporadic Cases of Legionellosis Associated with the Use of Domestic Ultrasonic Humidifiers

Two sporadic cases of legionellosis occurring in consecutive years were confirmed by positive antigenuria to <i>Legionella pneumophila</i> serogroup 1 in individuals with limited mobility who were confined to their homes. Both cases had a history of using ultrasonic humidifiers and of low exposure to other possible sources of infection. This study was conducted through an expanded epidemiological survey and home inspection. Samples were collected from domestic hot water and humidifiers. Environmental isolates were characterised by immunoagglutination and immunofluorescence. The Dresden panel is employed for the determination of groups and subgroups of serogroup 1. The amoebae were isolated by water filtration and subsequent cultivation of the filters. Identification of the isolates was conducted through the sequencing of PCR products. In both cases, epidemiological studies identified the ultrasonic humidifiers as the probable source of infection. The presence of <i>Legionella pneumophila</i> was confirmed in the sanitary water installation and in the humidifiers, where high values of <i>Legionella pneumophila</i> serogroup 1 counts were also obtained. The isolates were characterised as Olda Oxford and Olda OLDA. Furthermore, in addition to the Legionella isolates, the presence of <i>Vermamoeba vermiformis</i> was also identified in samples obtained from domestic hot water and humidifiers in one of the residential addresses under investigation. It has been demonstrated that humidifiers can act as an amplification mechanism for pathogenic microorganisms when they are not cleaned and maintained correctly. This can pose a health danger, especially to people with previous respiratory pathologies, the immunosuppressed, and the elderly. Therefore, it is of the utmost importance that professionals who recommend the therapeutic use of this equipment should issue warnings regarding the importance of its correct use, cleaning, and disinfection. Finally, humidifiers should be considered in epidemiological surveys and in the study of sporadic cases.