Potential of the polymerase chain reaction in the diagnosis of active Toxoplasma infection by detection of parasite in blood.

Blood samples from 54 patients presenting with acute toxoplasmic lymphadenopathy were tested for the presence of Toxoplasma gondii DNA using a nested polymerase chain reaction (PCR). PCR test results of a single blood sample obtained 2-23 weeks after onset of illness were positive for 19 (35%) of the 54 patients. Nine (53%) of 17 patients were positive by PCR when the initial blood sample was collected within the first 5 weeks of illness. In 7 of the 19 patients found positive, further blood samples were available, and subsequent clearance of T. gondii DNA from the blood was demonstrated. On the basis of positive findings among patients with acute toxoplasmosis and the absence of positive findings among 10 uninfected persons and 43 with past Toxoplasma infection, a positive PCR result appears to be a helpful indicator of active disease. However, since only 53% of patients with lymphadenopathy persisting < or = 5 weeks were positive, a negative PCR result does not exclude recent infection.