Long-term Persistence of Opisthorchis viverrini Antigen in Urine: A Prospective Study in Northeast Thailand

Abstract

Antigen detected in urine for the diagnosis of opisthorchiasis has a low daily variation; however, the longer term variability in antigen concentrations is unknown. In this study, we prospectively monitored Opisthorchis viverrini antigen concentrations for 30 consecutive days and at subsequent monthly intervals in a cohort of opisthorchiasis-positive individuals. On the basis of the monoclonal antibody-based ELISA, the profiles of antigen-positive rate and antigen concentration exhibited no significant change over 30 days with a mean proportion positive of 87.1% (range 73.7%-100%), and the average antigen concentration was 29.7 ± 2.2 ng/mL (mean ± SE). The urine antigen concentration at baseline was similar to the subsequent measurements at 2, 4, 6, and 10 months in the follow-up study (P > 0.05). The consistency and low daily and long-term fluctuation of O. viverrini antigen in urine demonstrates the reliability of urine assay for diagnosis of opisthorchiasis.

Figure 1.

The profiles of positive detection rate for opisthorchiasis and urine antigen concentration (nanograms per milliliter) over 30 days. The percentage urine antigen positive in each day (x-axis) correspond to the right y-axis (%) with an overall prevalence of 87.1 (black-dotted line). Data shown (dots) are urine antigen concentrations for individual participants, which correspond to the left y-axis (log-transformed antigen concentration, nanograms per milliliter). The red-dotted line indicates the cutoff value for a positive urine antigen assay (> 19.4 ng/mL). Urine samples were obtained from 35 to 42 participants per day.