Conceived and designed the experiments: ISK AG DR JRS. Performed the experiments: AG JRS. Analyzed the data: JCSF MGB. Wrote the paper: JCSF MGB DR JRS.
The authors have declared that no competing interests exist.
Urinary schistosomiasis is responsible for a variety of debilitating conditions; foremost perhaps are urinary tract pathologies (UTPs). Although portable ultrasonography can be used to detect UTPs visually, there is still a need for rapid morbidity assessment (henceforth referred to as RaMA) tools that can be deployed in the field during implementation, monitoring and evaluation of control programmes. We therefore aimed to determine associations between excreted urine-albumin, as measured using a HemoCue photometer, and UTPs, as detected by ultrasonography, in children and adults from an urinary schistosomiasis endemic area in Zanzibar.
In a survey of 140 school-children of both sexes (aged 9 to 15 yr) and 47 adult males (≥16 yr) on the island of Unguja, the prevalence of egg-patent urinary schistosomiasis was 36.4% (CI95 28.5–45.0%) and 46.8% (CI95 32.1–61.9%) (
This study indicates that albuminuria assays could be used as a RaMA tool for monitoring UTP prevalence during control programmes, as well as a tool for selecting those with more chronic bladder-wall lesions without resorting to ultrasonography.
Urinary schistosomiasis is a debilitating disease caused by a parasitic worm that dwells in the blood vessels, particularly those surrounding the human bladder wall. Although not directly associated with high patient mortality, this disease is linked to both short-term morbidity, e.g. visible blood in urine (acute), as well as long-term sequelae, e.g. urinary tract pathologies (chronic). Numerous control programmes based upon chemotherapy have been implemented in sub-Saharan Africa in an attempt to reduce the burden of disease inflicted, particularly in children. Although there are rapid tests to assess the prevalence of acute manifestations of disease (i.e. blood in urine), namely urine-reagent strips, monitoring of chronic manifestations (i.e. urinary tract pathologies) is still rather laborious, time-consuming and requires specialised equipment, e.g. portable ultrasonography, as well as highly trained staff. This study has attempted to evaluate associations between albuminuria (albumin in urine, a new application for the HemoCue photometer) and urinary tract pathologies, and consequently assess this new biochemical marker as a potential rapid proxy of chronic disease sequelae typical in children in areas where urinary schistosomiasis is of public health importance.
Urinary schistosomiasis is caused by infection with the parasitic trematode
More recently, with the availability of the HemoCue photometer assay (HemoCue, Ängelholm, Sweden), raised levels of excreted albumin in urine (>40 mg/L) have been found indicative of active
The aims of the present study were to assess the association between excreted urine-albumin, a known proxy of
The Ministry of Health, Zanzibar, and Imperial College of Science, Technology and Medicine, London, granted ethical approval for this study (application no. ICREC 03.36). At each school, written or oral informed consents were given by the school head-teacher and pupils, respectively. In the health centre, the participants granted their written informed consent, which were documented using checklists. Individuals found to be positive for infection with
The data were collected in May 2005 as part of the surveillance and monitoring of the second round of mass praziquantel treatment of the ‘
Each individual was interviewed by a member of staff of the Helminth Control Laboratory, Unguja, and asked a suite of 20 questions, recording demographic information (age, sex), general self-reported health conditions (e.g. headache, abdominal and back pains, pain on urination) and other variables (e.g. access to drinking water and treatment, as well as bladder continence). Copies of the questionnaire are available upon request (corresponding author).
Urine dipstick tests were conducted, yielding the urine's chemical/physical profile: pH, specific gravity, protein content, glucose, blood (micro-haematuria), nitrite and ketone levels, as well as leukocyte presence (Multistix, Bayer, UK). Urine-reagent strips (Hemastix, Bayer, UK) were used as a cross-check for micro-haematuria prevalence
Using a portable ultrasound machine (Aloka SSD-500, 3.5 MHz external probe, Aloka Inc., Japan), a variety of typical upper and lower urinary tract morbidities associated with urinary schistosomiasis (affecting organs such as kidneys, bladder, and ureters) were assessed and recorded in 132 school-children and 45 adult males, according to World Health Organization standardized examination protocols and severity scores
Micro- and macro-haematuria, visual opacity (turbidity) and raised urine-albumin concentrations (>40 mg/L) were tested qualitatively as alternative urinary schistosomiasis diagnostics, and for each, sensitivity (SS), specificity (SP), positive predictive value (PPV) and negative predictive value (NPV) were calculated against the ‘gold standard’ of parasitological diagnosis in urine filtrates. The same was done for urine-albumin assays as a potential rapid diagnostic test for UTPs against the ‘gold standard’ of ultrasonography. SS and SP indicate, respectively, the test's ability to identify correctly an individual as infected/diseased, or uninfected/healthy. PPV indicates the probability that in case of positive diagnosis, the patient is truly infected/diseased, whereas NPV indicates the probability that a negative diagnosis is in fact truly uninfected/healthy
Data were collected from each individual using pre-format data sheets, which were then entered onto an electronic format using Microsoft Excel™. The data thus collated were analysed using MS Excel™ and R statistical package v 2.8.1
Univariate and multivariate analyses were carried out using logistic regression to assess for potential statistical associations between (parasitological) infection status, albuminuria (defined as a concentration >40 mg/L according to
The mean age of the school-children was 11.4 years (median = 11 years), and 60% of individuals were between the ages of 10 and 12, with a female to male ratio of 0.80. The mean age of the adult males from the Chaani Health Centre was 29.6 years (median = 24), and 71% were between 20 and 40 years of age. A total of 84% of school-children and 64% of adult males reported to have access to potable water. Anti-schistosomiasis treatment coverage was close to 75% in school-children (ranging from 58% at Chaani school to 80% at Kinyasini school), whereas only 40% of the adult males reported to have had treatment. A total of 35% of school-children and 62% of adult males reported to feel pain on urination, and 14% of school-children and 23% of adult males reported to wake up at night for urination.
Urinary schistosomiasis was more prevalent (albeit not significantly,
Condition | School-children, both sexes (9–15 yr) | Adult males (≥16 yr) | |||
Chaani ( |
Kinyasini ( |
Mwera ( |
All schools ( |
Health Centre ( |
|
Urinary schistosomiasis (egg positive) | 26.7 (16.1–39.7) | 72.2 (54.8–85.8) | 20.5 (9.8–35.3) | 36.4 (28.5–45.0) | 46.8 (32.1–61.9) |
5.0 (1.0–13.9) | 11.1 (3.1–26.1) | 9.1 (2.5–21.7) | 7.9 (4.0–13.6) | 17.0 (7.7–30.8) | |
13.3 (5.9–24.6) | 19.4 (8.2–36.0) | 6.8 (1.4–18.7) | 12.9 (7.8–19.6) | 10.6 (3.6–23.1) | |
8.4 (2.8–18.4) | 41.7 (25.5–59.2) | 4.6 (0.6–15.5) | 15.7 (10.1–22.8) | 19.2 (9.2–33.3) | |
Micro-haematuria | 33.3 (21.7–46.7) | 83.3 (67.2–93.6) | 18.2 (8.2–32.7) | 41.4 (33.2–50.1) | 59.6 (44.3–73.6) |
Macro-haematuria | 11.7 (4.8–22.6) | 8.3 (1.8–22.5) | 2.3 (0.1–12.2) | 7.9 (4.0–13.6) | 4.3 (0.5–14.5) |
Turbid urine | 38.3 (26.1–51.8) | 63.9 (46.2–79.2) | 18.2 (8.2–32.7) | 38.6 (30.5–47.2) | 51.1 (36.1–65.9) |
Raised urine-albumin (>40 mg/L) | 31.7 (20.3–45.0) | 58.3 (40.8–74.5) | 15.9 (6.6–30.1) | 33.6 (25.8–42.0) | 27.7 (15.6–42.6) |
Urinary tract pathologies | 29.3 (18.1–42.7) | 75.0 (56.6–88.5) | 26.2 (13.9–42.0) | 39.4 (31.0–48.3) | 64.4 (48.8–78.1) |
Prevalence categories are classified according to the number of eggs per 10 ml urine.
UTPs were significantly more prevalent (
UTPs | Chaani ( |
Kinyasini ( |
Mwera ( |
All schools ( |
Health Centre ( |
||||||
Tissue | % | % | % | % | % | ||||||
Bladder | Irregular shape | 1 | 1.7 | 0 | 0.0 | 0 | 0.0 | 1 | 0.8 | 9 | 20.0 |
Wall thickness | 9 | 15.5 | 6 | 18.8 | 2 | 4.8 | 17 | 12.9 | 5 | 11.1 | |
Wall irregularities | 9 | 15.5 | 21 | 65.6 | 8 | 19.0 | 38 | 28.8 | 14 | 31.1 | |
Masses | 0 | 0.0 | 3 | 9.4 | 0 | 0.0 | 3 | 2.3 | 0 | 0.0 | |
Pseudopolyps | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | |
Positive score | 16 | 27.6 | 24 | 75.0 | 9 | 21.4 | 49 | 37.1 | 24 | 53.3 | |
Ureters | Pathology in right ureter | 2 | 3.4 | 1 | 3.1 | 0 | 0.0 | 3 | 2.3 | 4 | 8.9 |
Pathology in left ureter | 4 | 6.9 | 1 | 3.1 | 2 | 4.8 | 7 | 5.3 | 5 | 11.1 | |
Positive score | 4 | 6.9 | 2 | 6.3 | 2 | 4.8 | 8 | 6.1 | 6 | 13.3 | |
Renal Pelvis | Right hand side | 1 | 1.7 | 1 | 3.1 | 0 | 0.0 | 2 | 1.5 | 3 | 6.7 |
Left hand side | 3 | 5.2 | 0 | 0 | 0 | 0.0 | 3 | 2.3 | 3 | 6.7 | |
Positive score | 4 | 6.9 | 1 | 3.1 | 0 | 0.0 | 5 | 3.8 | 4 | 8.9 | |
Tissue walls | Calcification | 1 | 1.7 | 4 | 12.5 | 0 | 0.0 | 5 | 3.8 | 6 | 13.3 |
Overall positive score | 17 | 29.3 | 24 | 75.0 | 11 | 26.2 | 52 | 39.4 | 29 | 64.4 |
An overall, binomial score was attributed to the pathological state of individual tissues (positive score), as well as the urinary tract system as a whole (overall positive score), denoting the prevalence of any identifiable pathology according to WHO (1991) standardized methodology.
Comparing to the ‘gold standard’ of microscopy, detecting micro-haematuria by use of Hemastix reagent strips was by far the most reliable and rapid diagnostic tool for the detection of urinary schistosomiasis. The assay was found to be as reliable when used on school-children as when used on adult males (although specificity was lower in the adults) with, respectively, SS = 90.2% and 90.9%, SP = 86.5 and 68.0%, PPV = 79.3 and 71.4%, and NPV = 93.9 and 89.5% (
Method of diagnosis | Target population | Sensitivity (CI95) | Specificity (CI95) | PPV (CI95) | NPV (CI95) |
Macro-haematuria (self assessed) | Schools | 15.7 (7.0–28.6) | 96.6 (90.5–99.3) | 72.7 (39.3–94.0) | 66.7 (57.8–74.7) |
Health Centre | 9.1 (6.8–23.8) | 100.0 (86.3–100.0) | 100.0 (15.8–100.0) | 55.6 (40.0–70.4) | |
Visual turbidity (bar code chart) | Schools | 70.6 (56.2–82.5) | 79.8 (69.9–89.6) | 66.7 (52.5–78.9) | 82.6 (72.9–89.9) |
Health Centre | 72.7 (49.8–89.3) | 68.0 (46.5–85.1) | 66.7 (44.7–84.4) | 73.9 (51.6–89.8) | |
Albuminuria (conc.>40 mg/L) | Schools | 74.5 (60.4–85.7) | 89.9 (81.7–95.3) | 80.9 (66.7–90.9) | 86.0 (77.3–92.3) |
Health Centre | 31.8 (13.9–54.9) | 76.0 (54.9–90.6) | 53.8 (25.1–80.8) | 55.9 (37.9–72.8) | |
Micro-haematuria (urine reagent strip) | Schools | 90.2 (78.6–96.7) | 86.5 (77.6–92.8) | 79.3 (66.7–88.8) | 93.9 (86.3–98.0) |
Health Centre | 90.9 (70.8–98.9) | 68.0 (46.5–85.1) | 71.4 (51.3–86.8) | 89.5 (66.9–98.7) |
In all cases parasitological positivity by microscopy (eggs in urine) was the ‘gold standard’.
PPV = positive predictive value; NPV = negative predictive value; CI95 = 95% confidence interval.
In school-children, and after stepwise logistic regression, girls were found less likely to be infected by
At the univariate level, urinary schistosomiasis in children was found to be associated with prevalence of UTPs (OR = 11.4, CI95 4.6–27.9,
Elevated urine-albumin concentrations were common in both studied populations (33.6% of school-children and 27.7% of adult males,
At the univariate level, a raised urine-albumin level in school-children was found to be highly associated with micro-haematuria (OR = 138.7,
Population | Factor | Baseline | Category | Univariate Analysis | Stepwise Logistic Regression | ||||
OR | CI95 | OR | CI95 | ||||||
Chaani, Kinyasini and Mwera Schools | Micro-haematuria | Negative (≤trace) | Positive (>trace) | 138.7 | 29.6–649.6 | <0.0001 | 76.7 | 15.5–380.2 | <0.0001 |
UTPs | Negative | Positive | 7.1 | 3.0–16.7 | <0.0001 | – | – | – | |
Bladder | Negative | Positive | 7.6 | 3.2–17.6 | <0.0001 | – | – | – | |
Ureteral | Negative | Positive | 7.4 | 1.3–39.9 | 0.022 | – | – | – | |
Urinary schistosomiasis | Egg-negative | Egg-positive | 26.0 | 10.1–66.5 | <0.0001 | 3.1 | 0.9–10.5 | 0.070 | |
Chaani Health Centre | Micro-haematuria | Negative (≤trace) | Positive (>trace) | 5.5 | 1.1–28.6 | 0.043 | – | – | – |
Leukocytes in urine | Negative | Positive | 20.6 | 2.1–202.0 | 0.009 | 11.9 | 1.0–141.0 | 0.049 | |
Urine's specific gravity | Lower (<1.02 g/ml) | Higher (≥1.02 g/ml) | 4.8 | 1.1–20.4 | 0.035 | 5.7 | 1.0–32.2 | 0.050 | |
Bladder pathologies | Negative | Positive | 8.4 | 1.6–44.5 | 0.013 | 4.9 | 0.8–31.0 | 0.093 |
Explanatory variables included urine's chemical/physical properties (pH, specific gravity, protein content, glucose, nitrite and ketone levels, as well as leukocyte presence), urinary tract pathology prevalence (general and specific – bladder, renal pelvis and ureteric pathologies) and urinary schistosomiasis prevalence. Shown are significant associations at univariate level (after accounting for possible intra-correlations in the data), and stepwise (AIC-driven) logistic regression results, enabling identification of the most parsimonius, yet adequate, model for explaining elevated concentration of albuminuria.
At the univariate level, raised urine-albumin level in adult males was found to be associated with having micro-haematuria (OR = 5.5,
Albuminuria was able to identify ultrasonography-positive UTPs more effectively in school- children (SS = 61.5%, SP = 83.8%, PPV = 71.1%, NPV = 77.0%) than in the adult male population surveyed at Chaani Health Centre (SS = 37.9%, SP = 87.5%, PPV = 84.6%, NPV = 43.8%). Additionally, the diagnostic performance of this test increased somewhat when the diagnostic target was changed to specific pathology of the bladder instead of general UTPs (school-children: SS = 63.3%, SP = 83.1%, PPV = 68.9%, NPV = 79.3%; adults: SS = 45.8%, SP = 90.5%, PPV = 84.6%, NPV = 59.4%) (see
Diagnostic target | Diagnostic parameter | Schools | Health Centre |
UTPs | Sensitivity (%/CI95) | 61.5 (47.0–74.7) | 37.9 (20.7–57.7) |
Specificity (%/CI95) | 83.8 (73.8–91.1) | 87.5 (61.7–98.5) | |
PPV (%/CI95) | 71.1 (55.7–83.6) | 84.6 (54.6–98.1) | |
NPV (%/CI95) | 77.0 (66.8–85.4) | 43.8 (26.4–62.3) | |
Bladder pathologies | Sensitivity (%/CI95) | 63.3 (48.3–76.6) | 45.8 (25.6–67.2) |
Specificity (%/CI95) | 83.1 (73.3–90.5) | 90.5 (69.6–98.8) | |
PPV (%/CI95) | 68.9 (53.4–81.8) | 84.6 (54.6–98.1) | |
NPV (%/CI95) | 79.3 (69.3–87.3) | 59.4 (40.6–76.3) |
Ultrasound identification of pathologies was the ‘gold standard’. Refer to
PPV = positive predictive value; NPV = negative predictive value; CI95 = 95% confidence interval.
Urinary schistosomiasis in school-children was found to be significantly associated with gender, with boys being twice as likely to be infected as girls, in agreement with previous observations in Zanzibar
In the adult male population surveyed at Chaani Health Centre, urinary schistosomiasis was found to be associated with self-reported pain on urination, in particular around the bladder, and self-reported urine flow problems, illustrating the damage caused by egg expulsion through the urinary tract, even though no statistically significant association was found between active
In endemic, untreated populations, the prevalence and intensity of schistosomiasis is usually higher in children than in adults, giving rise to typically convex age-infection profiles
Importantly, Kinyasini was identified as a high infection school (overall infection prevalence of 72.2%), where 41.7% of the school-children were heavily infected with
The prevalence of UTPs was significantly higher in adult males (64.4%) compared to that in school-children (39.4%), reflecting the chronic nature of these sequelae. Additionally, this could be the result of ongoing chemotherapy campaigns targeting school-children, not only impacting infection prevalence and intensity, but also diminishing chronic disease progression
The use of urine filtration for detection of
Additionally, assays to detect albuminuria (>40 mg/L) were confirmed as an effective rapid diagnostic tool for urinary schistosomiasis in school-children (SS = 74.5%, SP = 89.9%, PPV = 80.9%, NPV = 86.0%), as previously reported by
In univariate analyses, albuminuria, as defined in
A raised urine-albumin level was found to be associated with the presence of micro-haematuria in school-children, whereas in adults a raised urine-albumin level was found to be significantly associated with the presence of leukocytes and higher urine's specific gravity (>1.02 g/ml). Although the presence of bladder pathologies was retained in the final, multivariate model of albuminuria for adult males, this variable was not statistically significant possibly because of lack of power due to small sample size. The latter observations (together with the absence of micro-haematuria as a significant covariate in the final statistical model for adult males) are possibly indicative of scarring in the urinary tract of adult males, whereas school-children appear to have raised albumin concentrations in their urine due to active egg expulsion and consequent haematuria.
Albuminuria can be indicative of kidney disease, hyperglycaemia, and hypertension
In view of the above, and for populations living in urinary schistosomiasis endemic areas of Africa, we propose a dual mechanism for explaining raised albumin concentrations in the urine of school-children, associated with ongoing perforation of the urinary tract by
In school-children (left), worms are likely located in the vesical plexus. As egg production ensues, eggs pass from the lumen of blood vessels into adjacent tissues, and many penetrate the bladder mucosa being shed into the urine (blue arrows). This causes tissue damage and subsequent haemorrhage (red broken lines and arrow) identifiable using urine-reagent strips (micro-haematuria) and/or visually (macro-haematuria). The presence of blood will increase the levels of albumin in urine (albuminuria). In adults (right), chronic manifestations of past and present
Targeting children at schools is thought to be highly effective in the control of schistosomiasis, not only because school-children are at higher-risk of infection
As the fight against schistosomiasis progresses, today's target populations, the school-children, will be tomorrow's adults. The impact of past and present control initiatives needs to be assessed not only in school-children but also in adults to help assess the progression of temporal and age-specific trends in infection and morbidity as chemotherapy-based control programmes advance. In adults, infection prevalence and intensities are often lower than in children at endemic equilibrium
In this paper, albuminuria (defined as albumin concentration in urine >40 mg/L) has been found to be a putative indicator of urinary tract pathologies, and it should be considered as a future rapid morbidity assessment tool to be used in conjunction with urine-reagent strips (e.g. Hemastix) for the screening and monitoring of urinary schistosomiasis, as well as associated chronic morbidity, before and during interventions, especially where ultrasonography may not be possible.
Diagnostic potential of albuminuria at the school level.
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Translation of the abstract into Portuguese by JCSF.
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Translation of the abstract into Spanish by MGB.
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We wish to thank the children and adults who participated in the study. We are also grateful to the Ministry of Health and Social Welfare of Zanzibar for their support during the “