Patients may be infected with various catalase-positive pathogens (e.g., Staphylococcus aureus, Aspergillus, Serratia, Burkholderia, Nocardia) and, in severe cases, may develop macrophage activation syndrome or hemophagocytic lymphohistiocytosis (4, 10–12), complicating the diagnosis. This evidence concerns the gene CAT and hemophagocytic syndrome.