Overall, data were collected from 21,528 children, including 4,944 (23.0%) from Coast Province, 3,658 (17.0%) from Rift Valley Province, 6,018 (28.0%) from Western Province, and 6,908 (32.1%) from Nyanza Province (Table 2). Errors in recording information in the field meant that information on age and sex of children were available for 21,312 children (99.0%) and 21,342 children (99.1%), respectively. The mean age of children was 9.8 years (standard deviation, SD 2.8 years) and the age range was 3 to 21 years. The percentage of boys (49.9%) and girls (49.2%) was comparable.
Overall, 32.4% (95% CI 30.1-34.8%) were infected with at least one STH species. A. lumbricoides was the most prevalent STH species (18.0%, 95% CI 15.7- 20.6%), followed by hookworm (15.6%, 95% CI 13.7-17.7%) and then T. trichiura (6.6%, 95% CI 5.4- 8.1%). The overall mean intensity of A. lumbricoides was 1,653 epg (95% CI 1372–1991), mean hookworm intensity was 64 epg (95% CI 51–81) and mean T. trichiura intensity was 33 epg (95% CI 10–104).
Overall, the prevalence and intensity of hookworm was higher in boys than girls (16.8%, 95% CI 14.8-19.0 vs. 14.5%, 95% CI 12.6-16.7, p < 0.001, 70 epg, 95% CI 55–88 vs. 58 epg, 95% CI 44–76, p = 0.015). Prevalence of A. lumbricoides and T. trichiura did not differ significantly by sex (p = 0.527 and p = 0.701). The intensity of T. trichiura infection was lower among boys than girls (27 epg, 95%CI 10–74 vs 40 epg, 95% CI 11–139, p = 0.002), while the intensity of A. lumbricoides did not differ significantly by sex (p = 0.310). Figure 2 presents prevalence and intensity of infection by age and sex. For both boys and girls, the prevalence of hookworm varied significantly by age group (p < 0.001), with prevalence highest among >14 year-olds; however, hookworm intensity did not vary significantly by age group (p = 0.250 and p = 0.051). Both the prevalence and intensity of A. lumbricoides varied significantly by age (p < 0.001), among boys and girls, and was highest among 6–7 year-olds. The prevalence of T. trichiura did not vary by age group (p = 0.355 for boys and p = 0.284 for girls), whereas the intensity of T. trichiura did vary significantly by age group (p < 0.001), with intensity being highest among 3–7 year-old male children and 8–9 and >14 year-old female children.
Table 2 summarizes the prevalence and intensities of STH infection by province. Patterns of STH varied markedly by province (p < 0.001), with hookworm most prevalent in Western Province and A. lumbricoides and T. trichiura most common in Rift Valley Province. Intensities of hookworm and A. lumbricoides infection also varied by province (p < 0.001), but there was only suggestive evidence for a difference in T. trichiura intensity by province (p = 0.055). The prevalence of moderate-heavy infection intensities was highest for A. lumbricoides in the Rift Valley (15.7%, 95% CI: 12.4-19.9, p < 0.001) and for hookworm in the Coast and Western Proince (0.5%, 95% CI: 0.2-1.1 and 0.5, 95% CI: 0.3-0.9, p < 0.001). The overall prevalence of moderate-heavy T. trichiura infections was 0.3% (95% CI: 0.2-0.6, p = 0.133). Figures 3,4,5 present the geographical variation of prevalence and intensity of infection by school and by district. Prevalence of infection varied markedly by school across the country: A. lumbricoides ranged from 0–71.3%; hookworm from 0–59.3%, T. trichiura from 0–64.4% (Table 2 and Figures 3A-5A). Prevalence by district varied from 0.3-45.5%, 0.2-44.3% and 0.2-30.2%, respectively (Figures 3D-5D). After removal of large-scale environmental effects, small-scale spatial patterns of prevalence, as indicated by Moran’s I statistic of spatial autocorrelation could be observed for hookworm (p = 0.045, p < 0.001) and A. lumbricoides (p < 0.001) in all regions, and for T. trichiura in Western, Rift Valley and Nyanza Provinces (p = 0.008) (Table 3).
The overall prevalence of S. mansoni was 2.1% (95% CI 1.2- 3.5) and the mean infection intensity was 12 epg (95%CI 4–36). In the Coast Province, where urine samples were collected, the prevalence of S. haematobium was 14.8% (95% CI 11.3-19.5) and the mean infection intensity was 16 eggs/10 ml urine (95% CI 10–26).
There was no significant difference by sex in the prevalence of S. mansoni (p = 0.868), prevalence of S. haematobium or intensity of S. mansoni (p = 0.362), whereas the intensity of S. haematobium was higher among boys than girls (32 eggs/10 ml, 95%CI 14–74 vs 12 eggs/10 ml, 95%CI 7–20, p = 0.033). Schistosoma infection prevalence and intensity by age and gender is shown in Figure 6. The prevalence (plinear = 0.001 and plinear = 0.018) and intensity (p < 0.001 and p = 0.031) of S. mansoni varied significantly by age-group among both sexes. While prevalence increased linearly with age, intensity of infection was lowest among 3–5 year-olds. The evidence for a variation in S. haematobium prevalence or intensity by age-group was weak among boys and girls (prevalence p = 0.308, p = 0.066; intensity: p = 0.640, p = 0.265).
Prevalences and intensities of Schistosoma infections are summarized in Table 4. S. mansoni infection prevalence and intensity varied by provinces (p < 0.001) and both were highest in Western Province. The prevalence of moderate-heavy S. mansoni infection intensity was also highest in Western Province (3.4%, 95% CI: 1.5-8.1. p < 0.001). There was also marked variability by school and district: school prevalence ranged from 0–64.8% for S. mansoni and 0-37% for S. haematobium; and mean district prevalences were 0–27.5% and 10-23%, respectively (Figures 7 and 8).
After removing environmental large-scale effects, positive spatial autocorrelation was observed only for S. mansoni prevalence in the Coast Province (p = 0.002), while the evidence for small-scale spatial structures was weak for S. mansoni in the other areas (p = 0.113) or for S. haematobium (p = 0.414). Moran’s I statistics of spatial autocorrelation are summarised in Table 3.
Finger-prick blood samples were collected from 492 children from 10 schools. Although too small to be meaningfully representative of the country, these ten schools were chosen to include schools in each of the four provinces where STH endemicity had been predicted. In these ten schools, the overall prevalence of anaemia was 31.3% (95% CI 21.7-45.1%) and the overall mean haemoglobin concentration was 12.6 g/dL (95% CI 12.0-13.2 g/dL). No significant differences were found in anaemia and haemoglobin concentration by sex (anaemia: p = 0.264; haemoglobin: p = 0.947), but there was significant variation by age (anaemia: p = 0.046; haemoglobin: p = 0.048), with anaemia decreasing and haemoglobin increasing with increasing age.
The overall prevalence of STH infection in these 10 schools was 33.3% (95% CI 25.7-43.1%, range of school prevalence: 18.5-65.7%) and the prevalence of schistosome infection was 14.3% (95% CI 7.1-28.7%, range of school prevalence: 0–34.3%). There was suggestive evidence for an association of anaemia with S. mansoni infection (p = 0.052) after adjusting for age and sex of children. However, there was no strong evidence for a positive association of anaemia with any or moderate-heavy hookworm, A. lumbricoides, T. trichiura, or S. haematobium infections and moderate-heavy S. mansoni infections.