Accuracy of parasitological and immunological tests for the screening of human schistosomiasis in immigrants and refugees from African countries: An approach with Latent Class Analysis

Abstract

BackgroundSchistosomiasis is a neglected infection affecting millions of people, mostly living in sub-Saharan Africa. Morbidity and mortality due to chronic infection are relevant, although schistosomiasis is often clinically silent. Different diagnostic tests have been implemented in order to improve screening and diagnosis, that traditionally rely on parasitological tests with low sensitivity. Aim of this study was to evaluate the accuracy of different tests for the screening of schistosomiasis in African migrants, in a non endemic setting.Methodology/Principal findingsA retrospective study was conducted on 373 patients screened at the Centre for Tropical Diseases (CTD) in Negrar, Verona, Italy. Biological samples were tested with: stool/urine microscopy, Circulating Cathodic Antigen (CCA) dipstick test, ELISA, Western blot, immune-chromatographic test (ICT). Test accuracy and predictive values of the immunological tests were assessed primarily on the basis of the results of microscopy (primary reference standard): ICT and WB resulted the test with highest sensitivity (94% and 92%, respectively), with a high NPV (98%). CCA showed the highest specificity (93%), but low sensitivity (48%). The analysis was conducted also using a composite reference standard, CRS (patients classified as infected in case of positive microscopy and/or at least 2 concordant positive immunological tests) and Latent Class Analysis (LCA). The latter two models demonstrated excellent agreement (Cohen’s kappa: 0.92) for the classification of the results. In fact, they both confirmed ICT as the test with the highest sensitivity (96%) and NPV (97%), moreover PPV was reasonably good (78% and 72% according to CRS and LCA, respectively). ELISA resulted the most specific immunological test (over 99%). The ICT appears to be a suitable screening test, even when used alone.ConclusionsThe rapid test ICT was the most sensitive test, with the potential of being used as a single screening test for African migrants.

Improved diagnosis of active Schistosoma infection in travellers and migrants using the ultra-sensitive in-house lateral flow test for detection of circulating anodic antigen (CAA) in serum

“…Diagnosing schistosomiasis via the detection of adult worm-related schistosomal circulating antigens has been employed extensively within populations living in endemic areas, but limited data is available on the detection of CAA in imported Schistosoma infections [ 19 – 21 ]. Because of its ultra-sensitive features and its capacity to diagnose all Schistosoma species, the UCP-LF CAA assay has much higher potential than the POC-CCA urine strip to be successfully implemented as a routine diagnostic laboratory test for the diagnosis of schistosomiasis in travellers and migrants [ 23 , 24 ].…”

Diagnostic study on an immunochromatographic rapid test for schistosomiasis: comparison between use on serum and on blood spot from fingerprick

“…This might be due to the composition of the nitrocellulose strip, which may not allow a proper flow of the blood drop and/or the development of the antibodies/antigen bond might be altered in the presence of proteins present in whole blood. However, it must be considered that, according to our previous diagnostic study, 10 the specificity of ICT on serum is not as high as the sensitivity (around 80%). Hence, an additional explanation for the lower number of positive results obtained by fingerprick might be that this method produces less false-positive results.…”

“…Recently, a diagnostic study compared various techniques for the immunological diagnosis of schistosomiasis, including western blotting, ELISA, circulating cathodic antigen dipstick test and an immunochromatographic (rapid) test (ICT). 10 The latter demonstrated the highest sensitivity (96%), with a negative predictive value of 98%, and it might be the ideal tool for screening, at least in non-endemic settings. Other immunological rapid tests for different parasitic infections (mostly for malaria 11 ) have been implemented for use with a blood drop from fingerprick, so that they can be performed in the field.…”

Schistosoma and Strongyloides screening in migrants initiating HIV Care in Canada: a cross sectional study

“…POC circulating cathodic antigen testing for Sc [44] and nucleic acid based diagnostic techniques have higher sensitivity than direct smear analysis [45,46] but currently are not routinely available for clinical screening in our non-endemic setting. Although emerging technologies are promising, a persistent difficulty in the diagnosis of helminth infections is the lack of a gold standard [47]. Despite its limitations, direct stool examination should have a role in screening in non-endemic settings when other direct parasitological tests or newer more sensitive tests are not routinely available.…”