Comparison of clinical and laboratory characteristics of patients fulfilling criteria for proven and probable human granulocytic anaplasmosis

To assess the value of clinical definitions for human granulocytic anaplasmosis (HGA) epidemiological, clinical and laboratory findings in 50 adult patients with proven HGA (Anaplasma phagocytophilum isolated from blood, and/or positive PCR result, and/or seroconversion or ≥4−fold change in serum IFA antibody titres to A. phagocytophilum) and 46 patients with probable HGA (demonstration of serum antibodies to A. phagocytophilum in titres ≥1:256) were compared. Patients with proven HGA were older (55 versus 43.5 years; p = 0.001), were more often treated with doxycycline (31/50, 62% versus 11/46, 23.9%; p < 0.001), more frequently reported chills (40/50, 80% versus 17/46, 36.9%; p < 0.001), myalgia (37/50, 74% versus 21/46, 45.7%; p = 0.005) and cough (10/50, 20% versus 2/46, 4.4%; p = 0.02), and had more often abnormal laboratory findings such as thrombocytopenia (45/50, 90% versus 22/46, 47.8%; p < 0.001), abnormal liver function test results (45/50, 87% versus 22/46, 47.8%; p < 0.001), leukopenia (38/50, 76% versus 21/46, 45.7%; p = 0.002) and elevated serum CRP concentration (48/50, 96% versus 31/46, 67.4%; p < 0.001). The dissimilarities imply that in some patients fulfilling criteria for probable HGA the signs and symptoms most likely are not the result of a recent infection with A. phagocytophilum and indicate that clinical definitions used in the present study have a distinctive value.