Evaluation of microscopy, serology, circulating anodic antigen (CAA), and eosinophil counts for the follow-up of migrants with chronic schistosomiasis: a prospective cohort study

Abstract

Background: An accurate test for the diagnosis and post-treatment follow-up of patients with schistosomiasis is needed. We assessed the performance of different laboratory parameters, including the up-converting reporter particle technology lateral flow assay to detect circulating anodic antigen (UCP-LF CAA), for the post-treatment follow-up of schistosomiasis in migrants attending a dedicated outpatient clinic in a non-endemic country.

Methods: Routine anti-Schistosoma serology results and eosinophil counts were obtained of patients with positive urine/stool microscopy and/or PCR (confirmed cases) or only positive serology (possible cases), and at least one follow-up visit at 6 (T6) or 12 (T12) months after praziquantel treatment. All sera samples were tested with the UCP-LF CAA assay.

Results: Forty-eight patients were included, 23 confirmed and 25 possible cases. The percentage seropositivity and median antibody titers did not change significantly during follow-up. UCP-LF CAA was positive in 86.9% of confirmed and 20% of possible cases. The percentage positivity and median CAA levels decreased significantly post-treatment, with only two patients having positive CAA levels at T12.

Conclusions: The UCP-LF CAA assay proved useful for the diagnosis of active infection with Schistosoma spp. and highly valuable for post-treatment monitoring in migrants, encouraging the development of a commercial test.

Keywords: Circulating anodic antigen (CAA); Diagnosis; Follow-up; Microscopy; Migrants; Schistosomiasis; Serology.

Fig. 1

Study flow chart. N = number of patients undergoing each investigation at each study time point; by definition, for patient classification, all patients underwent microscopy at baseline. Eos eosinophil count, F-U follow-up. Attended follow-up—both F-U time points = number of patients who presented to both T6 and T12 follow-up time points and how many of them underwent each of the listed diagnostic exams, independently from the result of the exam. Attended follow-up—only T6/T12 = number of patients who presented to only the T6 or only the T12 follow-up time point and how many of them underwent each of the listed diagnostic exams at the indicated time-point, independently from the result of the exam

Fig. 2

Results of eosinophilia and eosinophils count at baseline and baseline (T0) and follow-up time points (T6 and T12). a Percentage of patients with eosinophilia (eosinophils ≥ 450/μl blood); error bars represent 95% CI. No patient presented eosinophilia at T12. b Change in eosinophil counts over time in individual patients; log10 scale (the dashed line indicates the threshold for eosinophilia—eosinophils ≥ 450/μl blood). c Change in eosinophil counts over time (the dashed line indicates the threshold for eosinophilia—eosinophils ≥ 450/μl blood); box and whisker plots indicate median and IQR. Number of investigated patients with each test at each time point is indicated in Fig. 1. *p ≤ 0.05; **p ≤ 0.001; ***p ≤ 0.0001

Fig. 3

Results of routine serology tests at baseline (T0) and follow-up time points (T6 and T12). a Percentage of positive ELISA results; error bars represent 95% CI. b Change of ELISA serological index (SI) results over time in individual patients (the dashed line indicates the test positivity threshold SI ≥ 1.1). c ELISA serological index (SI) results (the dashed line indicates the test positivity threshold SI ≥ 1.1); box and whisker plots indicate median and IQR. d Percentage of positive ICT results; error bars represent 95% CI. Number of investigated patients with each test at each time point is indicated in Fig. 1

Fig. 4

Results of UCP-LF CAA test at baseline and baseline (T0) and follow-up time points (T6 and T12). a Percentage of patients with positive UCP-LF CAA test; error bars represent 95% CI. b Change in UCP-LF CAA levels over time in individual patients; log10 scale (the continuous dashed line indicates the threshold for positivity CAA 1 pg/ml; the interrupted dashed line indicates the threshold for indeterminate result CAA 0.5 pg/ml). c Change in UCP-LF CAA levels over time (the continuous dashed line indicates the threshold for positivity CAA 1 pg/ml; the interrupted dashed line indicates the threshold for indeterminate result CAA 0.5 pg/ml); box and whisker plots indicate median and IQR. Number of investigated patients with each test at each time point is indicated in Fig. 1. ***p ≤ 0.0001