A Systematic Review and Metanalyis of Soil Transmitted Helminths Infections Among Preschool and School-age Children in Ethiopia: Evaluation of Neglected Tropica Diseases (NTDS) Elimination Program by 2020

Background: Comprehensive nationwide on prevalence, geographic distribution of different species and time trends of soil-transmitted helminths (STHs) are lacking. Therefore, the aim of this study was to provide a summary and location of the available data on STHs infection among preschool and school-age children in Ethiopia. Methods: The search were carried out in Medline via PubMed, Scopus, Science Direct, Web of Science and Google Scholar on data published between 1995 to Fabruary 2020 for studies describing rate of STHs infection among preschool and school-age in Ethiopian. We followed Patient, intervention, Comparsion and Outcome (PICO) approach to identify the studies. Endnote citation manager software version X9 for Windows was utilized to collect and organize search outcomes (into relevant and irrelevant studies) and for removal duplicate articles . We conducted meta-regression to understand the trends and the source of heterogeneity and pooled the prevalence using ‘metaprop’ command using STATA software version 14. Results: A total of 29,311 of the 61,690 children examined during the period under review were infected with one or more species of intestinal parasites yielding an overall prevalence of 48 % (95%CI: 43-53%). The overall pooled estimate of STHs was 33% (95% CI: 28-38%). The prevalence was 44% (95%CI : 31% - 58%) in SNNPR, 34%((95%CI : 28% - 41%) in Amhara region, 31% (95%CI : 19% -43%) in Oromia region and 10% (95%CI : 7% - 12%) in Tigray region. Soil-transmitted helminths infection rate has been decreasing from 44% (95% CI:30-57%) pre-Mass Drug Administration (MDA) era (1997-2012) to 30% (95% CI:25-34%) post-MDA (2013-2020), although statistically not signicant (p = 0.45). A. lumbricoides was the predominant species with a prevalence of 17%. Conclusion: Southern Nations Nationalities and Peoples Region , Amhara and Oromia regions carry the highest burden and are categorized to Moderate Risk Zones (MRZ) and therefore, requiring mass drug administration (MDA) once annually with Albendazole or Mebendazole. Prevalence of SHTs decreased after MDA compared to before MDA, but the decline was not statistically signicant. < ≥ ( mix = Fifty two precent (52%) of the study participants were male. Majority (83) of the studies were cross sectional. Seventy three studies were about STHs in school-age children, 13 were about preschool-age and the rest were studies involved both preschool and school-age children. Thirty ve and twenty four studies used Kato-katz or incombination with other tools and formalin-ether concentartion plus direct microscopic method for screening stools, respectively. Formalin-ether concentration techinques in 19 studies, direct wet mount method in 5 studies, McMaster in 4 studies and Harada Mori (Test tube culture) technique in one study utilized as screening of stools. of reported from Amhara 36 (40.90%) and SNNPR 22(25%). followed by the Oromia region (22.7%), Tigray (9.1%), Benishangul-Gumuz region and Ababa city each with one (1.1%) study. None of the regions is classied as Risk (HRZ) according to world (WHO) risk classication. SNNPR, Amhara and Oromia regions recorded STH prevalence of 44%, 34%, 31%, respectively and are classied as moderate risk zones (MRZs) while, the rest of the regions and cities recorded prevalence estimates ranging between 1–10% and are classied as Low Risk Zones (LRZs).


Inclusion And Exclusion Criteria
We included observational studies or controlled clinical trials conducted between 1997 to Fabruary 2020 which documented the baseline prevalence or incidence of STHs and studies published in English language targeting both pre-school (< 5 years) and schoolage chikdren (≥ 5 years). We excluded case reports, case series, studies that compared the sensitivity and speci city of different methods for diagnosis of STHs and studies not reported either prevalence or incidence as outcome of interest.

Data Abstraction And Quality Assessment
Following preliminary assessment and downloading of the abstracts by two authors, they were assessed for agreement with the inclusion criteria. Irrelevant articles (articles which were out of the scope of the study) were excluded after assessment of the abstracts unless it was unclear to classify articles into irrelevant based on abstracts, where we downloaded the full-text for further clarity. Once articles deemed to be relevant, the full-text of the articles were downloaded for further detailed review. We extracted information on name of the rst author and year of publication, study design, gender, region of study, laboratory method identi cation of the parasites, total sample size, the number of positives for intestinal paraistes in general, number of positive for STHs in particular, and quality score for quality assessment. The Grading of Recommendation Assessment, development and Evaluation (GRADE) approach was used to assess the overall quality of evidence [18]. Studies were given one point each if they had probability sampling, larger sample sizes of more than 200, and repeated detection and upto four points could be assigned to each study. We regarded publications with a total score of 3-4 points to be of high quality, whereas 2 points represented moderate quality and scores of 0-1 represented low quality.

Statistical analysis
We used forest plots to estimate pooled effect size and effect of each study with their con dence interval (CI) to provide a visual summary of the data. A random-effects model was used in this meta-analysis because of anticipated heterogeneity. Statistical heterogeneity among studies was expressed as the Cochrane's Q test and I 2 , where a P < 0.05 and I 2 values of 0, 25, 50 and 75% were considered as no, low, moderate and high heterogeneities, respectively. Because we expected geographical variation and socioeconomic contexts might differ radically across these studies, subgroup analysis based on geography of region, age children included and year of publication. In addition to visual inspection for symmetry of the plot, we also used Begg's Funnel plot and Egger's regression test for quantitative evaluation of the possibility of publication bias. Meta-regression analysis was employed to identify the source of heterogeneity using regional states, age of children, publication years and study design as covariates. All reported P values were 2-sided and were statistical signi cant if P < 0.05.

Literature searches and selection
Our initial search of electronic databases such as Medline via PubMed, Scopus, Science direct, Web of Sciences and Google scholar yielded 953 articles and 3 articles manually from which 213 records remained after removing duplications. Upon screening the articles, 123 articles were further excluded; 112 were irrelevant because they were not speci cally about preschool or school-age children, 6 studies were about sensitivity and specify of diagnosis of STHs, and 5 articles were not about human. Upon further assessment for eligibility, 2 studies were excluded being review articles. Finally, 88 [6, 14,16, published studies between 1997 and Fabrauary 2020 ful lling the inclusion criteria were included in the nal analyses [ Figure 1]. The sample size of the included studies ranged from 100 [20] to 15,455 [14]. Atotal of 61,690 children with age of < 5 years (n = 5577) and ≥ 5 years ( n = 55731) or mix of both (n = 382) were recruited in the studies. Fifty two precent (52%) of the study participants were male. Majority (83) of the studies were cross sectional. Seventy three studies were about STHs in school-age children, 13 were about preschool-age and the rest were studies involved both preschool and school-age children. Thirty ve and twenty four studies used Kato-katz or incombination with other tools and formalin-ether concentartion plus direct microscopic method for screening stools, respectively. Formalin-ether concentration techinques in 19 studies, direct wet mount method in 5 studies, McMaster in 4 studies and Harada Mori (Test tube culture) technique in one study utilized as screening of stools. According to our quality assessment criteria, 43 publications were of high quality with a score of 3, 11 had a score of 2 indicating moderate quality and the remaining 34 were of low quality with a score of zero or one [ Table 1]. Southern Nations Nationalities and Peoples Region (SNNPR), Amhara, Oromia, and Tigray regions, respectively (Fig. 2). We also did subgroupanalysis to see the in uence of study design on prevalence. Interestingly enough, the prevalence was 48% ( 95% CI: 43-53%) for cross ectional study sdesign and therefore, the inclusion of other study designs has no in uence on the overall rate of infection ( not shown).

Overall Prevalence Estimate Of Soil-transmitted Helminthes (sths) And Heterogeneity
Soil-transmitted helminths detected in the studies were Ascaris lumbricoides, Hookworms, Trichuris trichiura and Strongyloides stercoralis. A total of 19, 678 of the 61,690 children examined during the period under review were infected with one or more species of STHs yielding an overall prevalence of 33%( 95%CI: 28-38%) with substantial heterogeneity (χ2 = 30360.02, P < 0.001; I 2 = 99.71%) (Fig. 3). The asymmetry of funnel plot visual inspection (Fig. 4) showed that the presence of publication bias which was statistically We did meta-regression analyses to search for the sources of heterogeneity. A univariate meta-regression between prevalence of STHs and age of children showed statistically signi cant correlation (P = 0.003, Fig. 5). However, year of publications, (P = 0.076), regional states (p = 0.70) and study design (p = 0.23) did not show a statistically signi cant correleation as shown in Table 2.  Fig. 6. The age related prevalence was 51% (95% CI: 45-56%) in school-age children and 32% (95% CI: 20-44%) in preschool-age children (p = 0.003) as shown in Fig. 7. Subgroup analysis by publication year showed that the pooled prevalence of STHs between 1995-2012 years was 44% (95% CI:30-57%) while, it was 30% (95%CI: 25-34%) for studies conducted between 2013-2020 years (Fig. 8). In summary, STHs were more common in SNNPR among school-age children in studies published between 1990-2012 as shown in Table 3. We performed subgroup analysis based on study design and the result showed that the prevalence of STHs was 34% (95% CI:29-39%) for cross sectional study, 25% (95% CI:23-28%), 4% (95% CI:3-5%) for prospective study and 20% (95% CI:15-26%) for case-control study (not shown). This indicates that the overall prevalence is almost the same as the prevalence of studies with cross sectional study design and was not affected by other study designs.
A univariate meta-regression between prevalence and age of children showed statistically signi cant correlation (Β = 1.03, 95% CI: 0.27 to 1.8, p = 0.01, supplementary le 6A). In Addition,meta-regression of the prevalence and regional states (β: -0.20, 95% CI: -0.40 to -0. 0.005, p = 0.045, supplementary le 6B) revealed a signi cant correlation. However, year of publication (β: -0.09, 95% CI: -0.79 to 0.61, p = 0.81) did not show a statistically signi cant relationship. In summary, Hookworms were more prevalent among children in Amhara region compared to other regions and among school-age children compared to preschool-age children ( Table 6).  (Table 7). For further details, the summary of species speci c STHs presented on Table 8.  Regional distribution of eligible studies and risk zones (RZs) for STHs infections The highest numbers of studies were reported from Amhara 36 (40.90%) and SNNPR 22(25%). These were followed by the Oromia region 20 (22.7%), Tigray 8 (9.1%), Benishangul-Gumuz region and Addis Ababa city each with one (1.1%) study. None of the regions is classi ed as High Risk Zone (HRZ) according to world health organization (WHO) risk classi cation. SNNPR, Amhara and Oromia regions recorded STH prevalence of 44%, 34%, 31%, respectively and are classi ed as moderate risk zones (MRZs) while, the rest of the regions and cities recorded prevalence estimates ranging between 1-10% and are classi ed as Low Risk Zones (LRZs).

Discussions
The purpose of current systematic review and meta-analysis of STHs infections data analysis among Ethiopian children was to measure the impact of the ongoing control and preventive measures in the country and support the efforts undertaken to control and eliminate neglected tropical diseases (NTDs) by nurturing or supplementing useful national epidemiological data. Such studies have the potential to guide concerned bodies to focus their efforts in highly endemic areas. Although several studies have been published from different regions of Ethiopia on STHs with the earliest scienti c literature dating back 1990s, the data on STHs infections remains unorganized and scattered. Therefore, organizing and locating information has the potential to inform and develop a comprehensive approach to control STH infections and target highly endemic areas with greater urgency.
The overall pooled estimate of STHs (33%) observed in the present review is in line with the study from south America 27·1% [111], but higher than study done in Iran (9.48%) [112] and Côte d'Ivoire (19.1%) [113]. The prevalence is lower than study from Nigeria (54.8%) [114] and repors from other Sub-Sharan African countres (52.4-65.8%). The variation between the ndings might be attributed to differences in sensitivity and speci city of diagnostic methodology, environmental factors such as soil moisture, humidity, temperature and level of participants' hygiene and sanitation. In addition, our review included more recent surveys that the ongoing MDA and Sustainable water, sanitation, and hygiene (WASH) programs decreased the prevalence of STHs in Ethiopian children unlike the systematic review from Nigeria which included old studies from the year 1985 [114] Subgroup analysis of the current review also showed that STHs are more common in SNNPR, Amhara and Oromia regions, although variation among the regional states was not statistically sigini cant ( p = 0.70). The majority of these infections are related to low standard of living, poor socioeconomic status, poor personal hygiene, and poor environmental sanitation. The higher prevalence of STHs infection among children in SNNPR, Amhara and Oromia regions might be also related to the high rainfall, forest and low temperature which favors the survival and transmission of the helminths in these regions. The lowest prevalence in Addis Ababa, capital city of Ethiopia, might to be due to advanced life style, good personal hygiene and good quality of life.
Our review suggests that the risk of STH infections has decreased from 44-30% in studies conducted between 1997-2012 and 2013-2020 respectively, although the decline is not statistically signi cant (p = 0.45). On one hand, prevalence might have declined in some parts due to improvement in living conditions globally, Ethiopia is not an exceptional and expansion of major deworming efforts. on the other hand, the increase in population growth in Ethiopia is tremendous and therefore, might have increased the numbers infected and resulted in slight decline in rate. it is also suggested that widespread of monotherapy of antiheminthics for deworming purpose might have facilitated the development of drug resistance and hence, decreased the rate of decline STHs in general and Hookworms in particular [115,116]. If environmental and behavioral conditions are not changed at the same time that chemotherapy program is being implemented, the prevalence will tend to return to original pretreatment levels through reinfection and therefore, need holistic approach [3,[116][117][118][119][120][121]. According to WHO risk categorization, our nding (33%) indicating that MRZ of STHs requiring MDA once annually, speci cally in SNNPR, Amhara and Oromia regions.
In relation to the species of STH, A. lumbricoides was the predominant species with a prevalence of 17% indicating that about one in six of Ethiopian children are living with Ascariasis. The current prevalence of the parasite is higher than the ndings from other counries such as Iran (0.75%) and Srilanka (2.8%) which indicated that indoor and outdoor biotic contamination of the living environment arising partly from improper disposal of human waste, and partly from the integration of the lives of humans and animals of Ethiopian community might account for the still high rate of of the infection in the country. The nding of the current review (17%) is in line with ndings from South America (15.6%), studies conducted in Amhara region, Ethiopia (16.8%) and the overall burden in Sub-Saharan African countries (15%) [122]. However, it was lower than results from Nigeria (44.6%), Rwanda (38.6%), Uganda (43.5%) [123], Kenya (24.3%) [124] and previous estimate in Ethiopia (37%). The observed differences might be due variation in some factors putting population at risk of acquiring STHs such as geographical variations, life style of the community, soil humidity and exposure to contaminated environments.. In the current review, the prevalence of A. lumbricoides signi cantly decreased from 25% in 1997-2012 to 14% in 2013-2020 (p = 0.006). There was a 49% decline in prevalence of A. lumbricoides observed before the implementation of MDA program in school children compared to post MDA. This risk reduction might be related to the improved sanitation, access to better water supply, improved personnel hygiene or the higher e cacy of the available treatments against A lumbricoides [115]. In support of this, a local study conducted on the e cacy of albendazole and mebendazole indicated that the drugs have 95% e cacy in decreasing the burden of the parasite in Ethiopia [125].
The pooled prevalence of 6% observed for T. trichiura was higher than the 1.9% and 3.4% reported from Uganda [112] and Rwanda [114], respectively. The present nding is however, lower than the reports of the disease burden of Sub-saharan Africa (13%) [106], Nigeria (18.2%) [110] and Cameroon (15.6%) [111]. The variations might be due to geographical variations, life style of the community, soil humidity and exposure to contaminated environments. Meta-regression anlaysis by year of publication revealed that the prevalence of T. trichiura decreased from 14% in 1997-2012 to 4% in 2013-2020 (p = 0.03). The reason behind the substantial decrease in prevalence of T. trichiura in the country during the study period might be due to the synergistic effect of overall improvements in sanitation, personnel hygiene and deworming programmes.
The nding of thee current review showed that the prevalence of hookworms was 12% indicating that the current nding is lower than others studies conducted in Nigeria (32.7%) [114] and Uganda (18.5%) [123]. However, it was higher than studies conducted in Kenya (0.4%) [124], Rawanda (1.8%) [126]and Cameroon (3.9%) [127]. In general, increments of prevalence in our data might be attributed to the re-infection rate, low coverage or unequal distribution of MDA in all regions of the country, level of poverty (walking bare of foot) and lack of good quality of life. For instance, most Ethiopian are living in rural area and engaged in agriculture. Engagement in agricultural pursuits remains a common denominator for adult human hookworm infection,who might be serve as reservoir for reinfection of children [121]. Hookworm did not show signi cant trend of decrement in prevalence between 1997-2012 (13%) as compared the years between 2013-2020. This is inconstrast to study conducted in Nepal where the revalence of Hookworms signi cantly decreased between 1990s to 2015[128].
Eliminating STHs as a public health has to go beyond preventive chemotherapy for school-age children, as other group at risk also serve as reservoir of infection (preschool children and pregnant women and even adults ), which might have resulted in slight decline again. It is also suggested that widespread of monotherapy of antiheminthics for deworming purpose might have facilitated the development of drug resistance and hence, decreased the rate of decline STHs in general and Hookworms in particular [115,116].
The strengths of our review include rigorous search of several databases and other sources to identify eligible studies on the large pediatric population infected by STHs and generate data for policymakers to strengthen or modify the already ongoing control and prevent measures on place. We also estimated the geographical distribution and identi ed risk areas that should be prioritized for MDA and other control interventions, which complement global efforts towards elimination of STHs and other parasitic infections by 2020. In addition, this work also highlighted the need for survey in areas where data are not available such as Somalia region, Afar region, Harari, Dire Dawa city and Gembela regions or scanty (Addis Ababa city and Benishangul-Gumuz region). There are a few limitations of the present meta-analysis. First, It is prudent to interpret the results of this study as 34(38.6%) of the included studies were low quality based on our quality assessment criteria. Second, in almost all of the studies included in this review, single stool sample examination were used despite multiple stool samples recommendation for standard diagnosis and therefore, there is possibility for underestimation of the prevalence. Almost all studies included the current analyses examined the stool specimens for many parasites at a time and the diagnostic performance of such an approach is not known compared to studies that examine solely for STHs, such diagnostic approach might affect the detection rate and prevalence estimates of STHs infections. Third WHO has recommended Kato-Katz method as the best and most reliable diagnostic tool with better e cacy, accuracy and predictive value than other techniques in resource poor settings [129]. However, only 39.8% of the studies reported the use of Kato-Katz method or in combination with other methods. Morbidity due to STH infections is a result of worm burden (number of eggs per gram of feces), otherwise called infection intesity. The disease prevalence is commonly combined with the intensity of infection to assess the epidemiological situation for STH infections and to classify communities into transmission categories, which enables the determination of the appropriate strategies for treatment and control [130]. However, only few studies (13 out of 88) reported the intensity of infection of species-speci c STHs and thus, di cult to reach on de nitive conclusion about intensity of infection of STH in Ethiopia children. Therefore, there is urgent need of large-scale study to assess the inetsnity of infection of STH in children using sensitive diagnostic tool on repeated stool sample. Finally, the review protocol was not registered a head of actual meta-analysis, which could be source of bias.