Detection of human polyomaviruses in urine from bone marrow transplant patients: comparison of electron microscopy with PCR.

BACKGROUND We studied electron microscopy (EM) as an appropriate test system for the detection of polyomavirus in urine samples from bone marrow transplant patients. METHODS We evaluated direct EM, ultracentrifugation (UC) before EM, and solid-phase immuno-EM (SPIEM). The diagnostic accuracy of EM was studied by comparison with a real-time PCR assay on 531 clinical samples. RESULTS The detection rate of EM was increased by UC and SPIEM. On 531 clinical urine samples, the diagnostic sensitivity of EM was 47% (70 of 149) with a specificity of 100%. We observed a linear relationship between viral genome concentration and the proportion of urine samples positive by EM, with a 50% probability for a positive EM result for urine samples with a polyomavirus concentration of 10(6) genome-equivalents (GE)/mL; the probability of a positive EM result was 0% for urine samples with <10(3) GE/mL and 100% for urine samples containing 10(9) GE/mL. CONCLUSIONS UC/EM is rapid and highly specific for polyomavirus in urine. Unlike real-time PCR, EM has low sensitivity and cannot quantify the viral load.