Impact assessment of onchocerciasis through lymphatic filariasis transmission assessment surveys using Ov-16 rapid diagnostic tests in Sierra Leone.

BACKGROUND: Onchocerciasis is endemic in 14 of Sierra Leone's 16 districts with high prevalence (47-88.5%) according to skin snips at baseline. After 11 rounds of mass treatment with ivermectin with good coverage, an impact assessment was conducted in 2017 to assess the progress towards eliminating onchocerciasis in the country. METHODS: A cluster survey was conducted, either integrated with lymphatic filariasis (LF) transmission assessment survey (TAS) or standalone with the LF TAS sampling strategy in 12 (now 14) endemic districts. Finger prick blood samples of randomly selected children in Grades 1-4 were tested in the field using SD Bioline Onchocerciasis IgG4 rapid tests. RESULTS: In total, 17,402 children aged 4-19 years in 177 schools were tested, and data from 17,364 children aged 4-14 years (14,230 children aged 5-9 years) were analyzed. Three hundred forty-six children were confirmed positive for Ov-16 IgG4 antibodies, a prevalence of 2.0% (95% CI 1.8-2.2%) in children aged 4-14 years with prevalence increasing with age. Prevalence in boys (2.4%; 95% CI 2.1-2.7%) was higher than in girls (1.6%; 95% CI 1.4-1.9%). There was a trend of continued reduction from baseline to 2010. Using data from children aged 5-9 years, overall prevalence was 1.7% (95% CI 1.5-1.9%). The site prevalence ranged from 0 to 33.3% (median prevalence = 0.0%): < 2% in 127 schools, 2 to < 5% in 34 schools and ≥ 5% in 16 schools. There was a significant difference in average prevalence between districts. Using spatial analysis, the Ov-16 IgG4 antibody prevalence was predicted to be < 2% in coastal areas and in large parts of Koinadugu, Bombali and Tonkolili Districts, while high prevalence (> 5%) was predicted in some focal areas, centered in Karene, Kailahun and Moyamba/Tonkolili. CONCLUSIONS: Low Ov-16 IgG4 antibody prevalence was shown in most areas across Sierra Leone. In particular, low seroprevalence in children aged 5-9 years suggests that the infection was reduced to a low level after 11 rounds of treatment intervention. Sierra Leone has made major progress towards elimination of onchocerciasis. However, attention must be paid to those high prevalence focal areas.

Community-wide prevalence and intensity of soil-transmitted helminthiasis and Schistosoma mansoni in two districts of Sierra Leone.

In Sierra Leone, nationally powered school-based surveys have documented significant progress in the control of soil-transmitted helminthiasis (STH) and schistosomiasis. In order to assess the district-level prevalence and intensity of infection among key at-risk groups outside of school age children (SAC), we conducted a multi-stage, cluster-sample household survey in Bo and Kenema districts in May 2018. From both districts, we examined 1,282 pre-school age children (PSAC), 730 school age children (SAC), and 517 adults over 14 years (including 387 women of reproductive age, or WRA) for STH and Schistosoma mansoni infection using Kato Katz technique. In Bo, STH prevalence was 8.0% (95% Upper Confidence Limit 10.2%) in PSAC, 6.4% (95% Upper Confidence Limit 9.0%) in SAC, 14.1% (95% Upper Confidence Limit 17.4%) in all adults and 11.9% (95% Upper Confidence Limit 17.4%) in WRA. In Kenema, STH prevalence was 18.1% (95% Upper Confidence Limit 20.5%) in PSAC, 17.3% (95% Upper Confidence Limit 20.7%) in SAC, and 16.9% (95% Upper Confidence Limit 20.5%) in all adults and 16.9% (95% Upper Confidence Limit 22.6%) in WRA. Hookworm species were the most prevalent of STH in both districts overall. The overall prevalence of S. mansoni was <10% in Bo and <20% in Kenema, and was similar across age groups. No moderate or heavy intensity STH infections or heavy intensity S. mansoni infections, as per World Health Organization (WHO) classification, were detected in either district. Sanitation variables, such as toilet access and quality, were independently associated with STH and S. mansoni infection. In Kenema, STH prevalence in SAC was within the WHO-defined range for annual treatment, whereas a previous nationally-powered survey estimated it to lie within the range of treatment once per two years. By utilizing community-based sampling, we were able to assess prevalence among WRA and make recommendations based on current guidance from WHO. To continue toward elimination of STH and S. mansoni as a public health problem, resources should be mobilized to increase access to and uptake of improved sanitation at community and household levels.

Achievements and challenges of lymphatic filariasis elimination in Sierra Leone.

BACKGROUND: Lymphatic filariasis (LF) is targeted for elimination in Sierra Leone. Epidemiological coverage of mass drug administration (MDA) with ivermectin and albendazole had been reported >65% in all 12 districts annually. Eight districts qualified to implement transmission assessment survey (TAS) in 2013 but were deferred until 2017 due to the Ebola outbreak (2014-2016). In 2017, four districts qualified for conducting a repeat pre-TAS after completing three more rounds of MDA and the final two districts were also eligible to implement a pre-TAS. METHODOLOGY/PRINCIPAL FINDINGS: For TAS, eight districts were surveyed as four evaluation units (EU). A school-based survey was conducted in children aged 6-7 years from 30 clusters per EU. For pre-TAS, one sentinel and one spot check site per district (with 2 spot check sites in Bombali) were selected and 300-350 persons aged 5 years and above were selected. For both surveys, finger prick blood samples were tested using the Filariasis Test Strips (FTS). For TAS, 7,143 children aged 6-7 years were surveyed across four EUs, and positives were found in three EUs, all below the critical cut-off value for each EU. For the repeat pre-TAS/pre-TAS, 3,994 persons over five years of age were surveyed. The Western Area Urban had FTS prevalence of 0.7% in two sites and qualified for TAS, while other five districts had sites with antigenemia prevalence >2%: 9.1-25.9% in Bombali, 7.5-19.4% in Koinadugu, 6.1-2.9% in Kailahun, 1.3-2.3% in Kenema and 1.7% - 3.7% in Western Area Rural. CONCLUSIONS/SIGNIFICANCE: Eight districts in Sierra Leone have successfully passed TAS1 and stopped MDA, with one more district qualified for conducting TAS1, a significant progress towards LF elimination. However, great challenges exist in eliminating LF from the whole country with repeated failure of pre-TAS in border districts. Effort needs to be intensified to achieve LF elimination.

Soil-transmitted helminth infection in school age children in Sierra Leone after a decade of preventive chemotherapy interventions.

BACKGROUND: Baseline mapping of soil-transmitted helminth (STH) infections among school age children (SAC) in 2008-2009 found high or moderate prevalence in 13 of the 14 districts in Sierra Leone. Following these surveys, mass drug administration (MDA) of mebendazole/albendazole was conducted biannually at national level targeting pre-school children (PSC) aged 12-59 months and intermittently at sub-national level targeting SAC. In addition, MDA with ivermectin and albendazole for eliminating lymphatic filariasis (LF) has been conducted nationwide since 2010 targeting individuals over 5 years of age. Each MDA achieved high coverage, except in 2014 when all but one round of MDA for PSC was cancelled due to the Ebola emergency. The objective of the current study was to determine the prevalence and intensity of STH infections among SAC after a decade of these deworming campaigns. METHODS: Seventy-three schools in 14 districts were purposefully selected, including 39 schools from the baseline surveys, with approximately two sites from each of low, moderate and high prevalence categories at baseline per district. Fresh stool samples were collected from 3632 children aged 9-14 years (male 51%, female 49%) and examined using the Kato Katz technique. RESULTS: The prevalence of STH infections in Sierra Leone decreased in 2016 compared to 2008: Ascaris lumbricoides 4.4% (95% confidence interval [CI]: 3.7-5.1%) versus 6.6% (95% CI: 0-25%), Trichuris trichiura 0.7% (95% CI: 0.5-1.1%) versus 1.8% (95% CI: 0-30.2%), hookworm 14.9% (95% CI: 13.8-16.1) versus 38.5% (95% CI: 5.4-95.1%), and any STH 18.3% (95% CI:17.0-19.5%) versus 48.3% (CI: 5.4-96.3%), respectively. In 2016, no district had high hookworm prevalence and four districts had moderate prevalence, compared with eight and four districts respectively in 2008. In 2016, the arithmetic mean hookworm egg count in all children examined was light: 45.5 eggs per gram (EPG) of faeces, (95% CI:\ 35.96-55.07 EPG); three (0.08%) children had heavy infections and nine (0.25%) children had moderate infections. CONCLUSIONS: Sierra Leone has made considerable progress toward controlling STH as a public health problem among SAC. As LF MDA phases out (between 2017 and 2021), transition of deworming to other platforms and water and sanitation strategies need to be strengthened to maintain STH control and ultimately interrupt transmission.

Schistosomiasis in School Age Children in Sierra Leone After 6 Years of Mass Drug Administration With Praziquantel.

Historic data and baseline surveys showed schistosomiasis as highly/moderately endemic in 7 of 14 districts in Sierra Leone, justifying annual/biennial mass drug administration (MDA) with praziquantel. MDA commenced in 2009 and reported treatment coverage had been above the World Health Organization recommended 75% of target population. Assessment in 2012 showed significant reduction in infection. In 2016, another national school-based survey was conducted to evaluate the progress. Two schools from each category (high, moderate or low) of endemic communities in each MDA district and five schools in non-MDA districts were selected. Fifty children (25 boys and 25 girls) aged 9-14 years were randomly selected per school. Parasitological examination of 1,980 stool and 1,382 urine samples were conducted. Overall Schistosoma mansoni prevalence in the seven MDA districts decreased to 20.4% (95% CI: 18.7-22.3%) in 2016 from 42.2% (95% CI: 39.8-44.5%) at baseline (p < 0.0001). Mean overall S. mansoni intensity of infection reduced to 52.8 epg (95% CI: 43.2-62.4 epg) in 2016 from 100.5 epg (95% CI: 88.7-112.3 epg) at baseline (p < 0.001). The prevalence of Schistosoma haematobium in the five MDA districts that had baseline prevalence data decreased to 2.2% (95% CI: 1.5-3.1%) in 2016 from 18.3% (95% CI: 16.3-20.5%) at baseline (p < 0.0001). Mean overall intensity of infection increased to 1.12 e/10 ml (95% CI: 0.55-0.1.70 e/10 ml) in 2016 compared to 0.47 e/10 ml (95% CI: 0.16-0.78 e/10 ml) in 2012 (p < 0.05) (no baseline data). No district was highly endemic in 2016 compared to three at baseline and there was no significant difference in prevalence or intensity of infection by sex for both species. This survey illustrated the significant progress made in controlling schistosomiasis in Sierra Leone. The fact that prevalence and intensity of infection showed an increase from the 2010 level suggested a detrimental effect of missing MDA due to the Ebola toward schistosomiasis control. The national program needs to continue the treatment and adopt a comprehensive approach including water, hygiene, and sanitation measures to achieve control and elimination of schistosomiasis.

Progress on elimination of lymphatic filariasis in Sierra Leone.

BACKGROUND: A baseline survey in 2007-2008 found lymphatic filariasis (LF) to be endemic in Sierra Leone in all 14 districts and co-endemic with onchocerciasis in 12 districts. Mass drug administration (MDA) with ivermectin started in 2006 for onchocerciasis and was modified to add albendazole in 2008 to include LF treatment. In 2011, after three effective MDAs, a significant reduction in microfilaraemia (mf) prevalence and density was reported at the midterm assessment. After five MDAs, in 2013, mf prevalence and density were again measured as part of a pre-transmission assessment survey (pre-TAS) conducted per WHO guidelines. METHODS: For the pre-TAS survey, districts were paired to represent populations of one million for impact assessment. One sentinel site selected from baseline and one spot check site purposefully selected based upon local knowledge of patients with LF were surveyed per pair (two districts). At each site, 300 people over five years of age provided mid-night blood samples and mf prevalence and density were determined using thick blood film microscopy. Results are compared with baseline and midterm data. RESULTS: At pre-TAS the overall mf prevalence was 0.54% (95% CI: 0.36-0.81%), compared to 0.30% (95% CI: 0.19-0.47) at midterm and 2.6% (95% CI: 2.3-3.0%) at baseline. There was a higher, but non-significant, mf prevalence among males vs females. Eight districts (four pairs) had a prevalence of mf < 1% at all sites. Two pairs (four districts) had a prevalence of mf > 1% at one of the two sites: Koinadugu 0.98% (95% CI: 0.34-2.85%) and Bombali 2.67% (95% CI: 1.41-5.00%), and Kailahun 1.56% (95% CI: 0.72-3.36%) and Kenema 0% (95% CI: 0.00-1.21%). CONCLUSIONS: Compared to baseline, there was a significant reduction of LF mf prevalence and density in the 12 districts co-endemic for LF and onchocerciasis after five annual LF MDAs. No statistically significant difference was seen in either measure compared to midterm. Eight of the 12 districts qualified for TAS. The other four districts that failed to qualify for TAS had historically high LF baseline prevalence and density and had regular cross-border movement of populations. These four districts needed to conduct two additional rounds of LF MDA before repeating the pre-TAS. The results showed that Sierra Leone continued to make progress towards the elimination of LF as a public health problem.

Impact of five annual rounds of mass drug administration with ivermectin on onchocerciasis in Sierra Leone.

BACKGROUND: Onchocerciasis is endemic in 12 of the 14 health districts of Sierra Leone. Good treatment coverage of community-directed treatment with ivermectin was achieved between 2005 and 2009 after the 11-year civil conflict. Sentinel site surveys were conducted in 2010 to evaluate the impact of five annual rounds of ivermectin distribution. METHODS: In total, 39 sentinel villages from hyper- and meso-endemic areas across the 12 endemic districts were surveyed using skin snips in 2010. Results were analyzed and compared with the baseline data from the same 39 villages. RESULTS: The average microfilaridermia (MF) prevalence across 39 sentinel villages was 53.10% at baseline. The MF prevalence was higher in older age groups, with the lowest in the age group of 1-9 years (11.00%) and the highest in the age group of 40-49 years (82.31%). Overall mean MF density among the positives was 28.87 microfilariae (mf)/snip, increasing with age with the lowest in the age group of 1-9 years and the highest in the age group of 40-49 years. Males had higher MF prevalence and density than females. In 2010 after five rounds of mass drug administration, the overall MF prevalence decreased by 60.26% from 53.10% to 21.10%; the overall mean MF density among the positives decreased by 71.29% from 28.87 mf/snip to 8.29 mf/snip; and the overall mean MF density among all persons examined decreased by 88.58% from 15.33 mf/snip to 1.75 mf/snip. Ten of 12 endemic districts had > 50% reduction in MF prevalence. Eleven of 12 districts had ≥50% reduction in mean MF density among the positives. CONCLUSIONS: A significant reduction of onchocerciasis MF prevalence and mean density was recorded in all 12 districts of Sierra Leone after five annual MDAs with effective treatment coverage. The results suggested that the onchocerciasis elimination programme in Sierra Leone was on course to reach the objective of eliminating onchocerciasis in the country by the year 2025. Annual MDA with ivermectin should continue in all 12 districts and further evaluations are needed across the country to assist the NTDP with programme decision making.

Changing patterns of health in communities impacted by a bioenergy project in northern Sierra Leone.

Large private sector investments in low- and middle-income countries are often critically evaluated with regards to their environmental, social, human rights, and health impacts. A health impact assessment, including a baseline health survey, was commissioned by the Addax Bioenergy Sierra Leone project in 2010. As part of the monitoring, a follow-up survey was conducted three years later. A set of health indicators was assessed at six impacted and two control sites. Most of these indices improved, particularly at the impacted sites. The prevalences of stunting, wasting, and Plasmodium falciparum in children under five years of age decreased significantly at impacted sites (all p < 0.05) and non-significantly at control sites. Anemia in children and in women of reproductive age (15-49 years) decreased significantly at impacted and control sites (p < 0.05 and p < 0.001, respectively). Health facility-based deliveries increased significantly at the impacted sites (p < 0.05). The prevalences of helminth infections in children aged 10-15 years remained approximately at the same levels, although focal increases at the impacted sites were noted. Access to improved sanitation decreased significantly (p < 0.05) at control and non-significantly at impacted sites. Water quality remained poor without significant changes. The epidemiologic monitoring of a bioenergy project provides a useful contribution for evidence-based decision-making.

Schistosoma mansoni infection after three years of mass drug administration in Sierra Leone.

BACKGROUND: Schistosoma mansoni was moderately-highly endemic in the northeast of Sierra Leone. The national neglected tropical disease control program started mass drug administration (MDA) with praziquantel (PZQ) in six districts in 2009 targeting primary school children only. The effort was scaled-up to seven districts in 2010 targeting school aged children (SAC) and at-risk adults. A cross-sectional sentinel site survey was conducted in 2012 after three rounds of MDA to evaluate the impact of the national program. METHODS: Twenty-six (26) sentinel sites were randomly selected from the baseline mapping survey sites stratified according to the baseline prevalence into high, moderate or low endemic category. Fifty (50) school children (25 males and 25 females) were randomly selected per site. Fresh stool samples were examined in the field using the Kato Katz technique. The results were compared with the baseline data. RESULTS: Program coverage of 94.8%, 77.1% and 81.7% was reported in 2009, 2010 and 2011 respectively. Independent monitoring in 2011 showed program coverage of 83.9%, not significantly different from the reported result in the same year. The overall prevalence of S. mansoni was 16.3% (95% CI: 14.4-18.4%) and mean intensity was 18.98 epg (95% CI: 11.46-26.50 epg) in 2012, representing 67.2% and 85.9% reduction from the baseline respectively. The proportion of moderately and heavily infected children was 3.3% and 1.2%, a significant reduction from 18.2% and 8.8% at baseline respectively. CONCLUSIONS: Sierra Leone has maintained effective MDA coverage with PZQ since 2009. Three rounds of MDA led to a significant reduction of S. mansoni infection in the country. In line with the significant progress made in controlling schistosomiasis, the national treatment strategy has been reviewed and MDA will be expanded to include school age children in low endemicity districts with the new national objective for the elimination of schistosomiasis. Sierra Leone is well on its way to eliminate schistosomiasis as a public health problem.

High level of Schistosoma mansoni infection in pre-school children in Sierra Leone highlights the need in targeting this age group for praziquantel treatment.

BACKGROUND: Schistosomiasis and soil-transmitted helminth (STH) infections are endemic in Sierra Leone. The consequences of these diseases to pre-school children are well understood. The national control program currently does not target this group of children for schistosomiasis, while mass drug administration (MDA) has been performed six monthly for STHs in children 12-59 months of age since 2006. METHODS: To assist the national decision on MDA strategy to control schistosomiasis and STH, three cross-sectional surveys were conducted in pre-school children in 2009-2011 as part of routine surveillance performed in different areas and in different phases of MDA, including known 'Hard to Reach' villages where consistently poor coverage results were seen in recent MDA. Thirty 4-5 year-old children were randomly selected per site and a stool sample from each child was examined by Kato-Katz thick smear. Pooled data were analyzed for schistosomiasis and separate sets of data were presented for STHs. In total 61 sites were surveyed and a total of 1803 children were examined. RESULTS: The overall prevalence and intensity of Schistosoma mansoni was 11.2% (95% CI 9.7-12.8) and 33.5 epg (95% CI 19.7-47.3). Relatively high level of infection was found in Kono (35.4% and 102.9 epg), Tonkolili (30.4% and 142.3 epg) and Koinadugu (20.8% and 47.0 epg). There were 8.1% of children 4-5 years old moderately or heavily infected with S. mansoni. Overall level of STH infections were generally low, with hookworm 8.4-22.8%, Ascaris lumbricoides 0.2-17.2%, and Trichuris trichiura 0.9-2.6% in three surveys. However, prevalence of hookworm and A. lumbricoides was relatively high in those hard-to-reach villages even two months after MDA. CONCLUSIONS: Relatively high levels of S. mansoni infections were found in children aged 4-5 years old in Sierra Leone, in line with geographical distribution of the disease observed in older children in the country. The results suggest that this group of children should not be neglected further in the schistosomiasis MDA and a global guideline is needed. Overall prevalence of STH infection was relatively low. Although there was no baseline data for direct comparison, it did show a marked reduction in STH infections, compared with historical data. However, relatively higher prevalence in hard-to-reach villages suggests the difficulty and quality of implementing MDA in such difficult locations, and more efforts and perhaps different delivery strategies are needed in these locations to increase the quality of MDA.

Combined spatial prediction of schistosomiasis and soil-transmitted helminthiasis in Sierra Leone: a tool for integrated disease control.

BACKGROUND: A national mapping of Schistosoma haematobium was conducted in Sierra Leone before the mass drug administration (MDA) with praziquantel. Together with the separate mapping of S. mansoni and soil-transmitted helminths, the national control programme was able to plan the MDA strategies according to the World Health Organization guidelines for preventive chemotherapy for these diseases. METHODOLOGY/PRINCIPAL FINDINGS: A total of 52 sites/schools were selected according to prior knowledge of S. haematobium endemicity taking into account a good spatial coverage within each district, and a total of 2293 children aged 9-14 years were examined. Spatial analysis showed that S. haematobium is heterogeneously distributed in the country with significant spatial clustering in the central and eastern regions of the country, most prevalent in Bo (24.6% and 8.79 eggs/10 ml), Koinadugu (20.4% and 3.53 eggs/10 ml) and Kono (25.3% and 7.91 eggs/10 ml) districts. By combining this map with the previously reported maps on intestinal schistosomiasis using a simple probabilistic model, the combined schistosomiasis prevalence map highlights the presence of high-risk communities in an extensive area in the northeastern half of the country. By further combining the hookworm prevalence map, the at-risk population of school-age children requiring integrated schistosomiasis/soil-transmitted helminth treatment regimens according to the coendemicity was estimated. CONCLUSIONS/SIGNIFICANCE: The first comprehensive national mapping of urogenital schistosomiasis in Sierra Leone was conducted. Using a new method for calculating the combined prevalence of schistosomiasis using estimates from two separate surveys, we provided a robust coendemicity mapping for overall urogenital and intestinal schistosomiasis. We also produced a coendemicity map of schistosomiasis and hookworm. These coendemicity maps can be used to guide the decision making for MDA strategies in combination with the local knowledge and programme needs.

Mass drug administration significantly reduces infection of Schistosoma mansoni and hookworm in school children in the national control program in Sierra Leone.

BACKGROUND: The first-ever round of school-based mass drug administration (MDA) with praziquantel together with mebendazole targeting school-aged children in endemic districts was conducted in 2009 by the National Neglected Tropical Diseases Control Program. To evaluate the impact of the treatment regimen, a cross-sectional sentinel site survey was conducted 6 months post-MDA. METHODS: Fifteen sentinel schools from six highly endemic districts (according to data from national and pre-MDA surveys) with Schistosoma mansoni affecting over 50% of the population, and moderate to high prevalence of hookworms (> 20%). Approximately 30 children aged 9-14 years were selected from each school and stool samples (one per student) were examined by the Kato-Katz method. RESULTS: The overall prevalence (and intensity) in these sentinel sites pre-MDA of S. mansoni was 69.0% (170.8 epg), hookworm: 41.7% (71.7 epg), Ascaris lumbricoides: 1.8% and Trichuris trichiura: 3.8%. Six months post MDA, the findings were S. mansoni: 38.2% (47.3 epg) and hookworm: 14.5% (8.7 epg), representing a reduction from pre-MDA levels of 44.6% (65.2%) and 72.3% (87.9%) respectively. The proportion of children who were moderately or heavily infected with S. mansoni fell from 35.6% pre MDA to 9.9% post MDA. CONCLUSIONS: Significant reduction in S. mansoni and hookworm infection was achieved by this first round MDA in school-going children in Sierra Leone. This reduction in infection burden can potentially contribute to a reduction of morbidity, such as anaemia, in these children.

Improved mapping strategy to better inform policy on the control of schistosomiasis and soil-transmitted helminthiasis in Sierra Leone.

BACKGROUND: Schistosomiasis and soil-transmitted helminthiasis (STH) are endemic in Sierra Leone confirmed by national mapping in 2008. To better inform planning of preventive chemotherapy strategy, another survey was conducted before mass drug administration (MDA) in seven districts according to the mapping results or local knowledge. Fifty-nine chiefdoms and one school in every chiefdom were selected. Thirty school children aged 9-14 years from each school (total: 1760) were examined by parasitological methods for infection with Schistosoma mansoni and STHs. RESULTS: The overall prevalence of S. mansoni was 40.2% (95% confidence interval (CI): 37.9-42.5%), particularly in Kailahun (63.3%), Kenema (46.7%), Koinadugu (41.9%) and Kono (71.7%). The results demonstrated the focal distribution of S. mansoni in Bo, Tonkolili and Bombali districts with prevalence ranging from 0.0-63.3%, 3.3-90.0% and 0.0-67.9% respectively. The arithmetic mean intensity of S. mansoni infection was 95.4 epg (95% CI: 61.4-129.5 epg), Heavy mean intensity of infection was found in Kailahun (120.2 epg), Kenema (104.5 epg), Koinadugu (112.3 epg) and Kono (250.3 epg). Heavy or moderate infection with S. mansoni occurred in 20.7% of children examined. Hookworm prevalence was moderate: 31.2% (95% CI: 29.1-33.4%), but high in Bo (50.0%) and Tonkolili (56.7%). Hookworm intensity of infection was light with a mean epg of 53.0 (95% CI: 38.4-67.7 epg). Prevalence and intensity of Ascaris lumbricoides (1.5%, 17.8 epg) and Trichuris trichiura (2.5%, 20.3 epg) was low. CONCLUSIONS: The prediction by previous spatial analysis that S. mansoni was highly endemic across north-eastern Sierra Leone was confirmed with a significant proportion of children heavily or moderately infected. The distribution of S. mansoni in Bo, Tonkolili and Bombali districts ranged widely, highlighting the importance of considering the nature of focal transmission in national mapping exercises. These results were used to refine the MDA for schistosomiasis control to chiefdom implementation units rather than the entire district in these 3 districts. The survey demonstrated that sufficient number of survey sites for schistosomiasis mapping in each district should be used to provide a better national planning of MDA activities, and that it is affordable with the contributions from all parties involved and national resources mobilized.