Urogenital schistosomiasis elimination in Zanzibar: accuracy of urine filtration and haematuria reagent strips for diagnosing light intensity Schistosoma haematobium infections

Abstract

BackgroundUrine filtration and microhaematuria reagent strips are basic standard diagnostic methods to detect urogenital schistosomiasis. We assessed their accuracy for the diagnosis of light intensity infections with Schistosoma haematobium as they occur in individuals living in Zanzibar, an area targeted for interruption of transmission.MethodsUrine samples were collected from children and adults in surveys conducted annually in Zanzibar from 2013 through 2016 and examined with the urine filtration method to count S. haematobium eggs and with the reagent strip test (Hemastix) to detect microhaematuria as a proxy for infection. Ten percent of the urine filtration slides were read twice. Sensitivity was calculated for reagent strips, stratified by egg counts reflecting light intensity sub-groups, and kappa statistics for the agreement of urine filtration readings.ResultsAmong the 39,207 and 18,155 urine samples examined from children and adults, respectively, 5.4% and 2.7% were S. haematobium egg-positive. A third (34.7%) and almost half (46.7%) of the egg-positive samples from children and adults, respectively, had ultra-low counts defined as 1–5 eggs per 10 ml urine. Sensitivity of the reagent strips increased significantly for each unit log10 egg count per 10 ml urine in children (odds ratio, OR: 4.7; 95% confidence interval, CI: 4.0–5.7; P < 0.0001) and adults (OR: 2.6; 95% CI: 1.9–3.7, P < 0.0001). Sensitivity for diagnosing ultra-light intensity infections was very low in children (50.1%; 95% CI: 46.5–53.8%) and adults (58.7%; 95% CI: 51.9–65.2%). Among the 4477 and 1566 urine filtration slides read twice from children and adults, most were correctly identified as negative or positive (kappa = 0.84 for children and kappa = 0.81 for adults). However, 294 and 75 slides had discrepant results and were positive in only one of the two readings. The majority of these discrepant slides (76.9% of children and 84.0% of adults) had counts of 1–5 eggs per 10 ml urine.ConclusionsWe found that many individuals infected with S. haematobium in Zanzibar excrete > 5 eggs per 10 ml urine. These ultra-light infections impose a major challenge for accurate diagnosis. Next-generation diagnostic tools to be used in settings where interruption of transmission is the goal should reliably detect infections with ≤ 5 eggs per 10 ml urine.Trial RegistrationISRCTN, ISRCTN48837681. Registered 05 September 2012 - Retrospectively registered.Electronic supplementary materialThe online version of this article (10.1186/s13071-018-3136-6) contains supplementary material, which is available to authorized users.

Performance of a real-time PCR approach for diagnosing Schistosoma haematobium infections of different intensity in urine samples from Zanzibar

“…However, four samples had counts between six and 721 eggs and it is not clear, why no DNA amplification occurred. There was no indication that storage time since sample collection, location of the participant's residence, sex or the microhaematuria level influenced the qPCR outcome in our study here, but labelling errors in 3% of samples have been suggested as potential reason for discrepant diagnostic results in another study from Zanzibar working with urine samples from the same surveys [7]. Most of the microhaematuria-positive but egg-negative and Dra1 DNA-negative urine samples were from females, and the explanation that the microhaematuria was caused by menstruation blood or other infections of the urogenital tract is self-evident.…”

“…Subsequently, urine samples with sufficient volume were vigorously shaken, and 10 ml were filtered through a filterholder containing a polycarbonate filter with a pore size of 20 μm (Sterlitech, Kent, WA, United States of America) using a standard 10 ml plastic syringe. The filter was then carefully transferred to a microscope slide, which was labeled with the participant ID, covered with hydrophilic cellophane soaked in glycerol, stained with Lugol's iodine and examined under the microscope for the presence and number of S. haematobium eggs by trained laboratory technicians [7]. Finally, on the day of collection, 10 ml of 10% of all urine samples were filled into Falcon tubes and stored in a − 20°C freezer in Pemba for future use.…”

“…The sensitivity of the qPCR was calculated as the proportion of Dra1 DNA-positives that were correctly identified when compared with the results of the reference test. Reference tests, though imperfect since they lack sensitivity to detect very light intensity infection [7], were i) urine filtration microscopy, ii) reagent strip tests, and iii) combined results of urine filtration microscopy and reagent strip test. Sensitivity was also calculated stratified by the different egg count (sub-) classes to assess the performance of the qPCR at very light intensity infections.…”

Urinary schistosomosis in patients of rural medical health centers in Kwale county, Kenya

“…In highly endemic areas, detection of hematuria could serve as a proxy indicator for S. haematobium infection identification (Anosike et al 2001;French et al 2007;Houmsou et al 2011). The validity of haematuria as a diagnostic criterion for urinary schistosomosis screening was discussed in a number of publications (Kinget al, 2013;Krauth et al 2015;Ochodoet al, 2015;Knopp et al, 2018). In our study, dipstick test sensitivity and specificity for detection of egg-positive urine were estimated at 68 % and 74 %, respectively (Table 3).…”

An update on non-invasive urine diagnostics for human-infecting parasitic helminths: what more could be done and how?

“…Some of these challenges include accurately estimating clinical morbidity, evaluating the impact of programmatic interventions, diagnosing preschool aged children and assessing new diagnostic tools (Stete et al, 2012;Knopp et al, 2013Knopp et al, , 2018Le and Hsieh, 2017). Recent concern has also been raised about urine-egg microscopy's poor sensitivity when attempting to detect 'ultra-light' infections, regarded as those that result in the expulsion of between only one and five eggs per 10 mL of urine (Knopp et al, 2018). Given the reproductive biology of schistosomes, just one infected individual excreting such minute numbers of eggs that may go on to infect and asexually reproduce within the appropriate intermediate freshwater snail host, potentially producing hundreds of cercariae per day, can cause the re-infection of an entire community (Colley et al, 2014).…”