Specificity of the Point-of-Care Urine Strip Test for Schistosoma Circulating Cathodic Antigen (POC-CCA) Tested in Non-Endemic Pregnant Women and Young Children

Abstract

The point-of-care urine based strip test for the detection of circulating cathodic antigen (POC-CCA) in schistosome infections is a frequently used tool for diagnosis and mapping of Schistosoma mansoni in school-aged children. Because of its ease of use, the test is increasingly applied to adults and preschool-aged children (PSAC), but its performance has not been specifically evaluated in these target groups. Recent observations have raised concerns about possible reduced specificity, in particular in pregnant women (PW) and PSAC. We thus explored specificity of the POC-CCA urine strip test (Rapid Medical Diagnostics, Pretoria, South Africa) in a non-endemic, nonexposed population of 47 healthy nonpregnant adults (NPAs), 52 PW, and 58 PSAC. A total of 157 urines were tested with POC-CCA, of which five (10.6%) NPAs, 17 (32.7%) PW, and 27 (46.5%) PSAC were positive. The highest scores were found in the youngest babies, with an infant of 9 months being the oldest positive case. On measuring pH, it appeared that all POC-CCA strongly positive urines were acidic (pH range 5-5.5), whereas addition of pH-neutral buffer to a subsample reversed the false positivity. We conclude that the POC-CCA test has reduced specificity in PW and infants younger than 9 months, but that the false positivity might be eliminated by modifications in the buffers used in the test.

Figure 1.

Flowchart of study participation. NPAs = nonpregnant adults; PSAC = preschool-aged children; PW = pregnant women.

Figure 2.

Percentage of total positives for POC-CCA (trace, 1+, 2+, and 3+) for all the three study groups. NPAs = nonpregnant adults (n = 47); POC-CCA = point-of-care–circulating cathodic antigen; PSAC = preschool-aged children (n = 58); PW = pregnant women (n = 52). *Indicates significant differences (P < 0.05) between the indicated groups and their number of positives (traces not included) based on POC-CCA. This figure appears in color at www.ajtmh.org.

Figure 3.

Scatterplot by visual score (negative, trace [0.5], 1+, 2+, and 3+) for NPAs based on gender, age, and percentage of total positives (A and B). For PW based on pregnancy trimester, age and percentage of total positives (C and D) and for PSAC based on gender, age, and percentage of total positives (E and F). NPAs = nonpregnant adults; PSAC = preschool-aged children; PW = pregnant women. This figure appears in color at www.ajtmh.org.