Several studies have been conducted quantifying the impact of schistosome infections on health and development in school-aged children. In contrast, relatively little is known about morbidity levels in preschool-aged children (≤5 years) who have been neglected in terms of schistosome research and control. The aim of this study was to compare the utility of available point-of-care (POC) morbidity diagnostic tools in preschool versus primary school-aged children (6–10 years) and determine markers which can be used in the field to identify and quantify Schistosoma haematobium-related morbidity. A comparative cross-sectional study was conducted to evaluate the performance of currently available POC morbidity diagnostic tools on Zimbabwean children aged 1–5 years (n=104) and 6–10 years (n=194). Morbidity was determined using the POC diagnostics questionnaire-based reporting of haematuria and dysuria, clinical examination, urinalysis by dipsticks, and urine albumin-to-creatinine ratio (UACR). Attributable fractions were used to quantify the proportion of morbidity attributable to S. haematobium infection. Based on results of attributable fractions, UACR was identified as the most reliable tool for detecting schistosome-related morbidity, followed by dipsticks, visual urine inspection, questionnaires, and lastly clinical examination. The results of urine dipstick attributes showed that proteinuria and microhaematuria accounted for most differences between schistosome egg-positive and negative children (T=-50. 1; p<0. 001). These observations were consistent in preschool vs. primary school-aged children. Preschool-aged children in endemic areas can be effectively screened for schistosome-related morbidity using the same currently available diagnostic tools applicable to older children. UACR for detecting albuminuria is recommended as the best choice for rapid assessment of morbidity attributed to S. haematobium infection in children in the field. The use of dipstick microhaematuria and proteinuria as additional indicators of schistosome-related morbidity would improve the estimation of disease burden in young children.
Urogenital schistosomiasis is a major parasitic disease caused by Schistosoma haematobium affecting children in Africa, with negative impacts on child health, growth and cognitive development [1]. Chronic infection with the parasite can cause anaemia, malnutrition, and organ complications such as bladder fibrosis and kidney failure [2]. Schistosome control programmes focus on preventive chemotherapy with the antihelminthic drug of choice, praziquantel, to reduce or prevent the development of severe morbidity due to schistosome infection, and thereby improving health of the infected individuals and communities [3]. In order to achieve these goals and evaluate the effects of control programmes, an understanding of the morbidity due to schistosome infection is essential [4]. This requires the use of reliable rapid diagnostic tools that can be used in the field [5]. In recent years progress has been made towards improving methods for measuring S. haematobium-related morbidity and various techniques have been evaluated in older children and adult populations [5]. For example, ultrasonography has been shown to be effective in detecting organ-specific morbidity [6,7]. However, the need for specialized equipment and trained personnel reduces its utility for large population studies in the field. Urinalysis has been used as a rapid indirect assessment tool for early urinary tract morbidity due to schistosomiasis [8]. In addition, standardized questionnaires recommended by the WHO for rapid screening of S. haematobium infection and morbidity have been extensively used in endemic regions [9]. Most of these studies have focused on older children, typically primary school-aged children (6–10 years), or older individuals. The WHO has recently recommended the inclusion of preschool children (aged 5 years and below) in schistosome control programmes [10], but the performance of the currently available point-of-care (POC) diagnostic tools for detecting schistosome-related morbidity have not yet been systematically evaluated in this age group. In addition, the utility of these POC tools has not been compared in a single study between preschool and primary school-aged (6–10 years) children, who are the current main targets of schistosome control programmes. Measuring the burden of schistosome disease in the whole population, including preschool children is important for the assessment of the effectiveness of control programmes and thus their prioritization and sustenance in affected countries (often with limited health budgets). Although extensive work has been done and a few recent studies published on morbidity due to S. mansoni infection in preschool children [11], to date there is still a paucity of studies quantifying the burden of S. haematobium-related morbidity in preschool children and the applicability of current POC morbidity diagnostics in these young children has not been extensively evaluated. To address this knowledge gap, we conducted a study in preschool and primary school children endemically exposed to S. haematobium infection assessing the utility of available diagnostic tools in identifying POC markers of schistosome-related morbidity. The first aim of the study was to characterise the morbidity in the children detected using the available POC tools. Since the morbidity markers currently used are general as opposed to being schistosome specific, they may detect morbidity unrelated to schistosome infection. Therefore, the second aim of the study was to relate the measures of morbidity to schistosome infection and determine the fraction of morbidity attributable to schistosome infection. The overall results would allow us to determine if POC diagnostics available for use in primary school-aged children can be reliably used in the field to quantify and monitor levels of morbidity attributable to S. haematobium infection in young children aged 5 years and below.
Ethical and institutional approval for the study was obtained from the Medical Research Council of Zimbabwe and the University of Zimbabwe, respectively. Permission to conduct the study was received from the Provincial Medical Director, the District Educational Officer, and Heads of schools in the study area. Study aims and procedures were explained to participants, and their parents/guardians in the local language, Shona. Prior to enrolment of study participants, written informed consent was obtained from parents/guardians and oral assent obtained from children. The children were recruited into the study on voluntary basis and were free to withdraw at any time with no further obligation. After sample collection, participants were offered treatment with the standard dose of 40 mg/kg praziquantel, administered by the local physician. The praziquantel drug was procured from a local supplier (Pharmaceutical and Chemical Distributors (Pvt) Ltd, Harare, Zimbabwe), registered and licensed to sell the drug in Zimbabwe. The cross-sectional study was conducted in Murewa district, in the north-east of Zimbabwe (31°90' E; 17°63' S) where S. haematobium is endemic. Prevalence of S. mansoni was low (<10%) [9] in this current study population as previously reported in other studies conducted in the same area [12,13]. There were no soil-transmitted helminths infections detected in this study population. Children aged 1–10 years were recruited from crèches, early child development centres, and local primary schools between February 28, and March 09,2012. To be included in this study, participants had to meet the following criteria: (1) been lifelong residents of the study area, (2) had no prior history of antihelminthic treatment (assessed by questionnaires administered to parents/guardians for all children), and (3) provided at least two urine, and two stool samples for parasitological examinations on consecutive days. The exclusion criteria were: (1) presenting with clinical symptoms of tuberculosis or malaria/fever, (2) recent major illness/operation, and (3) diagnosed positive for soil-transmitted helminths. None of the children were excluded based on these criteria. S. haematobium infection was determined by microscopic enumeration of eggs in urine processed using the standard urine filtration method [14]. Children were classified as infected if at least one parasite egg was detected in any of their urine samples collected on consecutive days. Infection intensity was defined as the arithmetic mean egg counts/10 mL of at least two urine samples collected on three consecutive days. Stool samples were processed using the Kato-Katz method, with duplicate thick smears (41. 7 mg) performed per sample [15], and subsequent egg enumeration by microscopy for the diagnosis of S. mansoni and soil-transmitted helminths. Children were designated infected with S. mansoni or soil-transmitted helminths if at least one parasite egg was detected in any of the two stool samples collected on consecutive days. A small proportion, 6. 0% (n = 18) of the children in our study was found positive for S. mansoni. We compared the morbidity characteristics of these children to those of a random sample drawn from age and sex matched S. mansoni negative children and no differences were observed, hence these children were kept in our study for the final analyses. None of the children in this study were found positive for STHs. We have recently shown that egg count lacks sensitivity in diagnosing light schistosome infections in children [16]. Thus, in addition to parasitology, IgM antibody responses directed against soluble egg antigens (SEA) were used to improve the diagnosis of S. haematobium infection. Details of the protocols used to quantify the serum antibody levels are published elsewhere [17]. Children were categorized as infected based on serology if their anti-egg IgM antibody levels were more than two standard deviations above the mean estimated from sera of negative controls, as outlined in our recently published study [16].
298 children (1–5 years: n = 104, median = 4 years; 6–10 years: n = 194, median = 8 years) fulfilled the study criteria (Fig. 1), and these comprised of 142 (47. 7%) males, and 156 (52. 3%) females. The overall prevalence of S. haematobium infection determined by parasitological examination was 35. 9% (95% CI: 30. 4–41. 4%). When looking at infection intensities, 28. 9% (95% CI: 23. 7–34. 0%) and 7. 0% (95% CI: 4. 1–10. 0%) of these children carried respectively light and heavy infection intensities according to the WHO categorizations [8]. Infection prevalence amongst primary children aged 6–10 years was 47. 9% (95% CI: 40. 8–55. 0%), and was significantly higher (χ2 = 35. 0; p<0. 001) compared to infection prevalence of 13. 5% (95% CI: 6. 8–20. 1%) observed in 1–5 years old children. However, there was no significant difference (χ2 = 0. 5; p = 0. 466) in the prevalence of infection between male and female children. Infection intensity increased significantly with age (r = 0. 4; p<0. 001), with the highest levels observed between the ages of 8–10 years. The prevalence of S. haematobium infection determined by serology was higher than that determined by egg counts in both age groups, 1–5 years: 52. 9% (95% CI: 38. 8–67. 1%), and 6–10 years: 84. 1% (95% CI: 78. 3–89. 9%). Dipstick-detected microhaematuria and proteinuria, contributed most to the observed variability in morbidity among children (taking into account urine’s physical characteristics, pH and specific gravity), as indicated by the strong correlations (see S1 Table). The variability of morbidity differed significantly between S. haematobium egg negative and positive children (T = -50. 7; p<0. 001) and between the two age groups (T = -19. 3; p<0. 001), however there were no differences by sex (T = -1. 5; p = 0. 089). Furthermore, the observed differences were evident from the large NMDS ordination output distances between the respective subgroup centres shown in Fig. 2. Based on the serological diagnosis of infection, significant differences were also observed by infection status (T = -14. 0; p<0. 001), age group (T = -6. 5; p<0. 001), but not by sex (T = -2. 5; p = 0. 068). In addition, microhaematuria and proteinuria alone explained about two-thirds of the overall variability due to differences between infected and uninfected children (detected by either parasitology or serology). The prevalence of dipstick microhaematuria was higher than questionnaire-reported haematuria, which in turn was also higher than visible haematuria (Fig. 3). The morbidity prevalence results illustrated in Fig. 3 revealed that children aged 6–10 years tended to report morbidity more frequently compared to parents/guardians of 1–5 years old children. In addition, albuminuria (detected by UACR) and dipstick proteinuria were observed in both age groups as shown in Fig. 3. A positive association of albuminuria with microhaematuria (φ = 0. 2, p = 0. 002), or proteinuria (φ = 0. 4; p<0. 001) was observed. In comparison to other diagnostic techniques investigated in this study, visual urine inspection, and clinical examination detected the least number of morbidity cases (Fig. 3). Results of multiple logistic regression analyses revealed a significant positive association (in order of strength of the association) of visible haematuria, albuminuria, microhaematuria, and proteinuria with S. haematobium infection detected by parasitology as shown in Table 1. In addition, S. haematobium infection prevalence determined by serology was also found to be significantly associated with albuminuria and proteinuria, adjusting for the effects of sex and age group (Table 1). Significant increases in prevalence of albuminuria (Odds ratio (OR) = 5. 5; p<0. 001), visible haematuria (OR = 4. 7; p<0. 001), microhaematuria (OR = 3. 4; p = 0. 005), and proteinuria (OR = 3. 3; p<0. 001) with infection intensity were observed. However, no significant associations between infection intensity and questionnaire-reported haematuria and dysuria, or clinical examination detected morbidity were found. Since the morbidity markers are not specific to schistosomes but are general markers of different physiological and biochemical processes, we went further to determine how much of the morbidity was attributable to schistosome infection. There was no significant difference in the estimated probability of detecting morbidity between 1–5 years and 6–10 years old children using each of the diagnostic tools (Table 2). In addition, from Table 2, it was observed that morbidity detected by dipsticks (microhaematuria and proteinuria), UACR (albuminuria), and urine inspection (visible haematuria) had prevalence ratios significantly greater than one. Clinical examination detected morbidity had the lowest prevalence ratio (Table 2). Furthermore, the results indicated that albuminuria was the dominant marker of schistosome attributable morbidity at population level, as well as amongst infected children (Fig. 4). Proteinuria and visible haematuria were also found to be highly attributable to schistosome infection among infected children. Although a high crude prevalence of microhaematuria was observed initially, the analyses revealed that a relatively small proportion of microhaematuria was attributed to S. haematobium infection (Fig. 4). The attributable fractions among infected children estimated by age group strata (see S1 Fig) showed a similar trend to the overall estimated attributable fractions noted above.
Our results confirm that schistosome infection in preschool children does result in significant morbidity. These findings are in agreement with recent studies on S. mansoni in Uganda [11] and S. haematobium in Malawi [37], reiterating the need for anthelminthic treatment in preschool children. This study has gone further to identify morbidity diagnostics with large fractions attributable to schistosome infection, highlighting detection of albuminuria as the best choice for rapid assessment of morbidity attributed to S. haematobium infection in children in the field. Finally the study showed that in S. haematobium endemic areas, preschool-aged children can be effectively screened for schistosome-related morbidity using the same diagnostic tools applicable to primary school-aged children and adult populations These findings are of clinical and public health importance, as these tools can be used to identify affected individuals or subgroups, thereby facilitating focused and timely delivery of treatment, as well as evaluate the effectiveness of interventions for improved control.
Schistosomiasis is a major parasitic disease affecting children in Africa, with impacts on health, growth and cognitive development. Recently, the World Health Organization has recommended inclusion of preschool-aged children (≤5 years) in schistosome control programmes. However, so far the performance of available morbidity diagnostic tools has not been thoroughly evaluated in this age group. To address this knowledge gap, we conducted a study in preschool children comparing the utility of currently available point-of-care tools for diagnosing Schistosoma haematobium-related morbidity, namely: questionnaire-reported haematuria and dysuria, clinical examination, dipstick urinalysis, and measurement of urine albumin-to-creatinine ratio (UACR). We also investigated the performance of these tools in older children (6–10 years). Our study identified UACR as the most reliable tool for detecting schistosome-related morbidity in terms of the morbidity attributable to schistosome infection, followed by dipsticks, visual urine inspection, questionnaires, and lastly clinical examination The study further showed that the tools currently used in school-aged children for diagnosing schistosome-related morbidity can be extended to preschool children, allowing easier integration of this age group into treatment and monitoring programmes.
Identifying and Evaluating Field Indicators of Urogenital Schistosomiasis-Related Morbidity in Preschool-Aged Children