Complement-mediated autoimmune haemolytic anaemia as an initial presentation of Legionnaires' disease

A 42-year-old diabetic man presented to the hospital with severe sepsis and multiorgan dysfunction. A probable respiratory source of sepsis was suspected because of suggestive clinical and radiological findings. He was critically ill and was therefore admitted to intensive care for further management including ventilatory support and renal replacement therapy. He was also found to have marked anaemia requiring multiple blood transfusions with clinical and laboratory evidence pointing towards severe haemolysis. Further workup for the aetiology of pneumonia established a diagnosis of Legionella by confirmatory tests namely legionella antigen in the urine and exponentially rising serum antibody titres. The cause for the severe haemolysis was found to be complement-mediated autoimmune haemolysis as determined by direct antiglobulin test positive for complement components C3 and negative for IgG. Such clinically significant autoimmune haemolysis as a presenting feature, rather than a late complication, has never before been reported in the literature.