Utilization of a real-time PCR assay for diagnosis of Babesia microti infection in clinical practice

Babesiosis is an emerging tick-borne disease mainly caused Babesia microti, a protozoan that infects erythrocytes. Microscopic examination of blood smears is the current gold standard for detection of Babesia infection, but this diagnostic test has several limitations. We developed and assessed the clinical utilization of a multiplex real-time PCR assay targeting the 18S rRNA gene of B. microti and the human gapdh gene. The limit of detection of this PCR assay was approximately 1–3 parasites/μl of blood. The assay showed a diagnostic sensitivity and probable specificity of 100% based on testing 145 retrospective and 185 prospective blood specimens from controls and patients with confirmed babesiosis. Notably, the PCR assay was more sensitive than blood smear examination in patients during and following anti-babesia drug therapy. Our study suggests that PCR testing is as good or better than a blood smear for detection of B. microti in routine clinical practice. PCR testing may confirm the presence of babesiosis in patients whose level of infection is too low for reliable microscopic detection.