Performance of Urine Reagent Strips in Detecting the Presence and Estimating the Prevalence and Intensity of Schistosoma haematobium Infection

School-Based Epidemiology of Schistosoma haematobium Infection in Kharif District of Amran Governorate, North of Yemen: Need for Chemopreventive Strategy Revisiting

Background

Urogenital schistosomiasis is a persistent public health problem in many rural areas of Yemen. Since 2014, Schistosoma haematobium epidemiology has not been assessed in Amran governorate, north of Yemen, where S. haematobium is known to be highly endemic. Therefore, this study determined the prevalence and risk factors associated with S. haematobium infection among schoolchildren in Kharif district of the governorate.

Methods

A cross-sectional survey was conducted among 529 schoolchildren aged 7 to 15 years in Kharif district. Data on children's demographics, clinical features, behaviors, and infection-related environmental factors were collected using a structured questionnaire. The urine filtration technique was used to detect and count S. haematobium eggs, and chemical reagent strips were used to detect microhematuria. The number of eggs per 10 mL of urine (EP10mL) was used to estimate the intensity of infection, which was classified as light (≤50 EP10mL) or heavy (>50 EP10mL). Multivariable binary logistic regression analysis was used to identify predictors of infection.

Results

Light-intensity S. haematobium infection was prevalent among 34.8% of schoolchildren in Kharif district, with a 95% confidence interval (CI) ranging from 30.7 to 38.8. Infection was significantly associated with microhematuria (P <0.001) and self-reported dysuria (P = 0.003). Family ownership of agricultural land was significantly associated with S. haematobium infection among schoolchildren [odds ratio (OR) = 1.8, 95% CI: 1.10-3.17; P = 0.030], which was further identified as an independent predictor of infection (adjusted OR = 2.2, 95% CI: 1.21-3.95; P = 0.010).

Conclusion

A considerable proportion of schoolchildren in Kharif district have light-intensity S. haematobium infections, mostly presenting with microhematuria and self-reported dysuria. The district's level of risk should be updated to moderate. Consequently, the chemopreventive strategy needs to be revisited to treat all school-age children biennially, regardless of enrollment status.

Clinical sensitivity and time-to-result of a cascaded pooled testing approach for assessing the prevalence and intensity of Schistosoma haematobium infection

BACKGROUND

This study compared the clinical sensitivity and the time-to-result of an individual testing (IT) and a cascaded pooled testing approach (CPT; a positive test result in a pooled sample triggers examination of smaller-sized pools or individual samples) for assessing the prevalence and the intensity of Schistosoma haematobium infection. We also compared the sensitivity of the CPT in detecting S. haematobium infection when deploying urine filtration microscopy (UFM) vs. urine reagent strips (URS), and testing 10 mL vs. 15 mL of urine.

METHODOLOGY/PRINCIPAL FINDINGS

Between October 2021 and April 2022, S. haematobium eggs were counted in urine samples collected from school-aged children living in the Afar and Gambella Regional States of Ethiopia. Urine samples were collected at baseline (n = 1,288), and one month after administration of praziquantel (n = 118). All urine samples were processed through both an IT and a CPT approach (pools of 5, 10, 20, and 40 individual samples), deploying UFM (10 mL) and URS (10 mL). In addition, 15 mL urine was processed through the CPT deploying UFM. At baseline, the prevalence of S. haematobium infection estimated when using UFM and deploying a CPT approach was significantly lower (17.3%) compared to an IT approach (31.5%). The clinical sensitivity of the CPT in detecting S. haematobium eggs was 51.7%. The sensitivity increased significantly as a function of increasing log transformed urine egg counts (UECs) of the individual samples (OR 2.71, 95%CI 1.63 - 4.52). The sensitivity was comparable when the amount of urine examined was 10 mL (51.7%) vs. 15 ml (50.8%), and when UFM was used for testing vs. URS (51.5%). The mean log UECs estimated following the CPT approach was lower compared to the estimate by the IT (p <0.001). UECs of the individual samples estimated using the IT and CPT approaches were moderately correlated (r = 0.59 when 10 mL and 15 mL urine was examined after pooling). CPT reduced the time needed for processing urine samples and testing for S. haematobium infection by 29% with UFM and by 27.7% with URS.

CONCLUSIONS/SIGNIFICANCE

CPT based on UFM and URS techniques may help to rapidly identify areas with higher prevalence of S. haematobium infection (hotspots) in a population. However, the performance of this approach in estimating the prevalence of infection may be compromised, particularly in endemic areas with low intensity infection.

Review of Recent Prevalence of Urogenital Schistosomiasis in Sub-Saharan Africa and Diagnostic Challenges in the Field Setting

Human schistosomiasis is one of neglected tropical diseases that remain highly prevalent in sub-Saharan Africa (SSA). Human schistosomiasis is mainly caused by two species, Schistosoma haematobium and S. mansoni, leading to urogenital and intestinal schistosomiasis, respectively. The World Health Organization (WHO) recommends mass drug administration (MDA) with praziquantel as the primary method of global intervention. Currently, MDA with praziquantel covers over half of the target population in endemic SSA countries. However, an accurate diagnosis is crucial for monitoring and evaluating the effectiveness of MDA. The standard diagnosis of both urogenital and intestinal schistosomiasis relies on the microscopic identification of eggs. However, the diagnostic sensitivity of this approach is low, especially for light or ultra-light infections. This is because Schistosoma eggs are laid inside of the venous plexus of the urinary bladder or mesenteric vein, where the adult flukes live. Approximately half of the eggs circulate in the blood vessels or are packed in neighboring tissues, while the remaining half are expelled into the lumen of the urinary bladder or intestine intermittently when the blood vessels are ruptured. In the field setting, the accuracy of any diagnostic method is critical for proper management of the intervention. The present article reviews the recent prevalence of urogenital schistosomiasis in SSA and highlights the practical limitations of diagnostic methods such as urine microscopy, urine reagent strips, molecular diagnosis, and ultrasound scanning in the field setting. Despite continuous global efforts to eliminate schistosomiasis over the past 20 years, many areas still remain endemic in SSA. No single diagnostic approach achieves acceptable sensitivity and specificity in the field setting. Therefore, any field survey should employ a combination of these methods based on the purpose of the study to accurately monitor and evaluate urogenital schistosomiasis. Based on diagnostic values and a cost-benefit analysis, a urine reagent strip test can replace urine microscopy in the field setting. The WHO criteria by ultrasound diagnosis should be updated including the echogenic snow sign and contour distortion.