Planning and implementation of preventive chemotherapy strategy recommended by the WHO depends on a good understanding of endemic situation of the diseases in each district [29–31]. This is particularly the case for schistosomiasis because of its focal distribution in areas, close to snail-infected water sources which in Sierra Leone are altitude related . The mapping survey conducted in 2008, prior to the MDA of the national integrated NTD control programme, gave an overall picture of S. mansoni and STH endemic situations in Sierra Leone . Together with spatial prediction, the northeast half of the country was classified as highly endemic for S. mansoni, which required annual MDA for all school-age children plus adults at high risk. However, in the 2008 survey relatively few (four) sites per district were used, therefore there was a need to validate the predicted prevalence maps and confirm the PCT strategy in chiefdoms that were not surveyed. Furthermore, in three districts (Bo, Bombali and Tonkolili) it was unclear from the 2008 mapping whether MDA was justified and if so how frequently it should be performed.
The results of this current survey confirmed the high endemicity of S. mansoni in Kailahun, Kenema, Koinadugu and Kono districts and in Eastern chiefdoms of Bombali and Tonkolili districts, suggesting a convincing prediction by the spatial analysis in these areas. The results also confirmed that some chiefdoms in Bo district were indeed endemic and therefore qualified for MDA. This highlights the importance of sampling methods in schistosomiasis survey to meet the nature of focal transmission of the disease.
The results also provided valuable data on the intensity of infection of S. mansoni and STHs in school aged children in these areas which were not recorded in the 2008 mapping survey. School aged children in Kailahun, Kenema, Koinadugu and Kono districts are relatively heavily infected with S. mansoni with arithmetic mean intensities of infection of over 100 epg. There are 20.7% of children heavily or moderately infected with S. mansoni in these seven districts. This highlights the need for intervention to prevent severe morbidity in their later life . Based on these survey data, MDA was planned and these highly endemic districts have so far received two rounds of treatment In 2009 school-going children were targeted, and 562,980 received praziquantel and 549,701 received mebendazole. In 2010, all school-aged children and at risk adults were targeted, and 1,826,284 received praziquantel and 1,000,042 received albendazole .
The focal distribution of S. mansoni is most clearly demonstrated in Bo, Bombali and Tonkolili with prevalence widely ranging from chiefdom to chiefdom. In the context of such districts in Sierra Leone, it is important to plan the implementation strategy according to the chiefdoms rather than the whole districts. This complementary survey provided such a tool to enable the national program managers and district health teams to plan and refine their MDA activities in conjunction with the 2008 mapping results. This is a clear demonstration that a detailed mapping survey with sufficient number of survey sites across the endemic areas, in particular for focal diseases such as schistosomiasis, is needed in order to better plan the control activities. There is a dilemma currently for the national teams in terms of the need of detailed mapping and the funds available. The current survey of about $310 per site also demonstrated the affordability of such mapping surveys with the contributions from all parties involved and national resources mobilized.
Low prevalence and intensity of A. lumbricoides and T. trichiura and moderate prevalence and light intensity with hookworm highlight remarkable reductions in comparison with pre-war studies [18–20, 23, 24]. The impact on STH of the annual distribution of ivermectin and albendazole in the NTDCP's lymphatic filariasis elimination programme since 2007 and various school-based deworming programs performed by the Wood Food Program and NGOs since 2004 has been discussed previously [26, 33]. Although of light intensity, the moderate prevalence of hookworm infections and widespread anaemia in children in Sierra Leone according to the national data confirm the desirability of using albendazole as the drug of choice as albendazole has a better cure rate for hookworm infections .
The current survey provided a significantly improved tool for planning the MDA activities in each district, however there are certain limitations in the methodology used. Firstly, the sampling method of survey sites based upon accessibility, though not uncommon for schistosomiasis, may not represent the true endemicity level in chiefdoms, as those schools in hard-to-reach locations may be heavily affected by schistosomiasis. Secondly, by adding formalin to the stool samples, it may have diluted the stool samples and caused underestimation of the results. However, considering the rural conditions in the post-war Sierra Leone, it was not possible to process and examine the stool samples on site, and therefore, preservation of the samples was a necessary trade-off to avoid disintegration of helminth, particularly hookworm, eggs. Thirdly, only one Kato-Katz slide was used for the diagnosis, and the low sensitivity of this method may have caused underestimation of the prevalence and slight overestimation of the intensity of infection. However, considering the morbidity control strategy for schistosomiasis and STH by preventive chemotherapy in the current national control programme, such slight misestimation would not make much difference to the overall objectives of the national programme.