Introduction: Legionella micdadei are gram-negative bacilli living in soil and aquatic habitats. They are responsible for less than 10% of legionellosis, but have a propensity to affect people suffering from immunodeficiency. Lung cavitations may also occur in this population. Isolation of L. micdadei on clinical samples requires specific culture media that are not routinely used. Moreover, serologic methods and urinary assays are specific for Legionella pneumophila serogroup 1 (the most frequent serogroup isolated from clinical specimens), and lack sensitivity for diagnosing L. micdadei infection. As a consequence, this diagnosis is difficult to confirm.
Case report: We report here a severe case of community-acquired legionellosis due to L. micdadei, in a patient under immunosuppressive medications and high-dose corticosteroids for rheumatoid arthritis. The source of his infection was hypothesized to be his continuous positive airway pressure device, which was regularly cleaned with tap water instead of sterile water, thus potentially resulting in Legionella contamination.
Conclusions: L. micdadei must be considered as a possible cause of community-acquired severe pneumonia in case of immunodeficiency. For outpatients, advice concerning the cleaning of aerosols-generating devices at home must be emphasized.
Keywords: Legionella micdadei; continuous positive airway pressure device; immunodeficiency; obstructive sleep apnea; pulmonary abscess.