Multi-pathway assessment of fecal contamination in urban areas of Abidjan: The case of Abobo municipality

The presence of septic tank effluents in open spaces and roads due to poor fecal sludge management (FSM) in low-income cities represents a source of fecal contamination and potential risk of fecal-oral disease transmission. This study aimed at assessing fecal contamination exposure through six exposure pathways in Abobo, District of Abidjan in Coˆte d’Ivoire. The public health risk was evaluated in two clusters to identify the dominant exposure pathways and to compare which populations were most exposed. The SaniPath approach used included behavioral surveys (transect walk, household survey, school survey and community survey) and laboratory analysis. Surveys were conducted among 200 households, 6 schools and 4 community groups. In addition, 120 environmental samples were collected (in 2 clusters of 6 pathways with 10 samples per pathway per cluster). The colony forming unit (CFU) of E . coli was determined in samples using the surface plating technique on agar medium. Bayesian analyses were performed to estimate the distributions of fecal concentration and contact frequency, and exposure to fecal contamination was estimated using the Monte Carlo method with 1000 iterations. The highest concentrations of E . coli were observed in open drains (6.1 log CFU/ml), gullies (6 log CFU/ml) and soil (5.8 log CFU/ml) samples. The dominant exposure pathways were determined by multiplying the dose and the percentage of


Introduction
The world is currently experiencing high rates of urban population growth.Most of this increase is expected to occur in cities in low-and middle-income countries in Africa and Asia [1].The World Health Organization (WHO) estimates that by 2100 AD, Africa will have 39% of the world's population, almost as much as Asia [1].This rapid and uncontrolled urbanization has led to several challenges, including degradation of the urban environment, global climate change, increasing water stress, infrastructure deficits and rapid expansion of poor settlements [2].In Sub-Saharan Africa, the on-site sanitation system concerns 65% and 100% of the urban population and rural population respectively [3].In Abidjan, the capital city of Co ˆte d'Ivoire, about 60% of the households use on-site sanitation [4].However, there is poor management of excreta with 90% being discharged in the environment without any treatment [5], and it has been well established that environmental risk factors are an important cause of the burden of disease [6].
The Municipality of Abobo is the most densely populated area in the District of Abidjan with 91.1 hbts/km 2 [7].Previous studies in Abobo highlighted a link between solid and liquid waste management and the development of pathologies affecting the population [8] with most septic tanks overflowing into the street, while households illegally connect to open drains [9].In some neighborhoods of Abobo, microbiological contamination has been revealed in the food consumed by the population, particularly the "attie ´ke ´" food sold on the street [10].Although several studies have been carried out on sanitation issues in the municipality, the pathways of exposure, their quantification and location seem unexplored to date and need to be investigated.The few studies that have been carried out on fecal contamination have been limited to drinking water as an exposure pathway.Other potential exposure pathways related to fecal indicator transmission have not been well studied [11].However, pathways of fecal exposure are generally interconnected and are a public health concern [11].The lack of accurate information and data may be one of the reasons that municipal authorities are inefficient in improving hygiene and health conditions.This study was carried out to assess exposure to fecal contamination in two clusters of the Abobo municipality through several exposure pathways.The SaniPath exposure assessment tool has been used to identify and compare the risk of exposure to fecal contamination across multiple exposure pathways associated with inadequate sanitation and fecal sludge management [12].This tool has been deployed in several countries around the world including Africa, America and Asia [13].The SaniPath tool used in our study allows evaluating the exposure to fecal contamination, according to several fecal exposure pathways in the public and private domains, which can assist the communal authorities in their improvement efforts [14].The outcomes of using this initiative could be useful for actors involved in urban sanitation management to better target interventions for specific improvements.

Study area
This study was carried out in the District of Abidjan, located in the South of Co ˆte d'Ivoire.This district includes 13 municipalities with different socio-demographic conditions Fig 1 .The municipality of Abobo is situated in the North of Abidjan between latitudes 5˚20' and 52 9' North and longitudes 3˚57' and 4˚06' West and covers an area of about 100 km 2 .It borders the Banco National Park to the West, which is the largest underground water reservoir in the District of Abidjan [15].According to the 2021 national population and housing census, Abobo has 1,340,083 inhabitants living in twenty-seven neighborhoods [7].The configuration of these neighborhoods varies according to socio-economic status [16].The average monthly precipitation varies from 19.46 mm in January to 326.34 mm in June [17].In addition, the municipality is affected by undeveloped natural hollows, some of which are used by local residents as spillways for both solid and liquid waste [18].

Data collection
The SaniPath tool uses data from behavioral (household, school, and community) and environmental samples to assess the exposure to fecal contamination [12].The tool was applied to the two clusters to assess exposure to fecal contamination, notably in gully water.Most households use the gutters in these areas for emptying their household water and sometimes also the water coming from their latrines.The SaniPath approach includes socio-environmental surveys (transect walk, household survey, school survey, and focus group) and laboratory analysis using E. coli detection and enumeration.The collected data are used to perform Bayesian analyses to generate the percent of the population exposed and the average fecal exposure dose.In this study, data collection was done, according to SaniPath protocols, in the four different steps described in the Fig 2.
Choice of neighborhoods and exposure pathways.A literature review followed by a geographic survey was conducted to learn more about the socio-environmental conditions of the different neighborhoods in the target municipality, and the municipality area was subdivided into two groups: Cluster I and Cluster II.Cluster I is composed of unplanned and informal settlements, mainly with common courtyards where the households are sharing toilets and pit latrines.The main part of the population lives in poverty, characterized by a lack of sanitation facilities.Cluster II includes well planned settlements, which are made up of single-family homes where individual households have private toilets and latrines as well as sanitary facilities.There is sanitation infrastructure and the majority of the population lives in medium-to high-income neighborhoods.Cluster I includes the Sagbe ´, Kennedy and Banco neighborhoods, while Cluster II comprises the Anador, Dokui and Cite ´Coccinelle neighborhoods.
Analysis of the exposure pathways was done by conducting transect walks through the clusters to observe the behavior of the populations, as well as noting possible sampling sites for each of the sample types.Table 1 shows the six pathways selected after this transect walk.Furthermore, due to the large number of gullies throughout the area, the sampling considered the gullies instead of surface water.In practice, gullies were observed in most of the streets we walked and are mainly used by the population as informal wastewater drains.
Behavioral surveys.The behavioral survey involved households, local communities and schools.In practice, 100 households were randomly selected per cluster as recommended by the Sanipath tool, corresponding to 200 households.In each cluster, two groups of at least 15 people were identified for the community survey.One group was composed entirely of In accordance with the Sanipath tool protocol, the school selection was based on the following criteria: i) being in a cluster neighborhood, and ii) having a second grade class of less than 30 students of both girls and boys [19].At this level, the pupils are between 10 and 15 years old, they can more easily understand the objectives of the study and respond to the questions.
All types of surveys contained questions addressing the contact behavior of the adults and children with the fecal exposure pathways.Questions were asked about the frequency of consumption of street food and stored drinking water, and the frequency of contact with open drains, gullies, and floodwaters.
Five investigators conducted behavioral surveys for two weeks during the month of May 2021.The team was composed mainly of students who were previously trained in investigative techniques at the Felix Houphoue ¨t Boigny University.The training focused on how to introduce oneself to a household, how to present the goals of the survey, and how to address the various issues with the interviewees.Furthermore, permits from the municipal authorities and the pre-school and primary school inspectors were obtained before carrying out the surveys.

Environmental sample collection
The sampling campaign was carried out during the rainy season in June 2021 as this season provides a "worst case" scenario because many homeowners illegally empty their sanitation storage facilities during heavy rains [20].In each cluster, 10 samples were collected from each of the exposure pathway as recommended by the SaniPath Protocol [12].Hence, 120 environmental samples of soil, street food, flood water, drinking water, gully water and open drain water were collected during this sampling campaign (2 clusters of 6 pathways with 10 samples per pathway per cluster) (Fig 4).It should be noted that information regarding both behavioral and environmental contamination were collected from the same geographic areas.This ensures that as much reliable information as possible is gathered from each cluster.All samples collected were stored at 4˚C and chemical and microbiological analyses were performed within the six hours following the sampling.Laboratory sample processing.The microbiological analyses of the samples were carried out, according to the directives of the French association of standardization [21].All samples collected were analyzed for E. coli, as an indicator of fecal contamination.The choice of E. coli is justified by its being the main indicator of fecal contamination and because it can be detected using simple laboratory methods.Finally, it is the recommended fecal indicator for the SaniPath tool [22,23].
The membrane filtration technique was applied only to stored drinking water samples.It consisted of passing 100 ml of drinking water sample through a 0.45-micron membrane filter.The other samples were analyzed using the plating technique, which was made by performing four successive dilutions (10 −1 , 10 −2 , 10 −3 and 10 −4 ) for each sample and then spreading 0.1 ml of the different dilutions on a Petri dishes surface containing Rapid E. coli 2 agar.
All samples from each technique were placed in an incubator at 37˚C for 24 hours and colonies that appeared with a purple coloration (characteristic of E. coli) were counted.
Then, the concentration of E. coli was calculated by averaging the concentrations of the four dilutions, according to the following equation: With: Cs: colony forming unit in the reference volume Vs (Vs = 1mL) in CFU/mL N: Sum of all the colonies counted in the plates from the dilutions F1 (1:10), F2 (1:100), F3 (1:1000), F4 (1:10000) n1: number of plates counted for dilutions F1, F2, F3, F4 v1, v2, . . .vi: test volume used for dilutions F1, F2, F3, F4 (v1 = 0.1mL) F1, F2, F3, F4: dilutions used for the test samples Vs: reference quantity chosen to express the concentration of micro-organisms in the sample The collected data was entered into the SaniPath tool, which automatically generates results in several forms for each exposure pathway [14].Specifically, the tool presents the results in the form of people plots generated from the microbiological and behavioral data.These people plots provide information, such as the percentage of the population (adults or children) exposed to fecal contamination by a specific pathway, the magnitude of the average E. coli dose ingested per month and the percentage of the population that is not exposed to fecal contamination by that pathway.Afterwards, we determined the risk of exposure (E) which is unitless.This was performed by multiplying the dose by the percentage of exposure and then transforming the value to log scale.However, all pathways with E greater than 10 (high risk) or within a log 1 interval around the maximum value of E will be considered dominant [12].Nevertheless, if E is less than 1 (low risk) for all pathways, there is no dominant pathway.

Data analysis
The data analysis was performed, according to the Sanipath methodology, behavioral and microbiological data were used to estimate exposure to fecal contamination at each pathway.
The SaniPath Tool uses both behavioral and microbiological data to estimate exposure at a cluster level.The statistical model used by this tool assumes that the concentrations of E. coli in the environmental samples were modeled using log normal distributions, while the frequencies of contact were modeled using negative binomial distributions [12].Distribution parameters were estimated using Bayesian framework by JAGS [24].So, 1000 iterations of Monte Carlo simulation were conducted to assess the exposure to fecal contamination by pathway, cluster and age group.This simulation was performed using the distribution parameters related to the E. coli concentrations in the samples, the frequencies of the behaviors, as well as the intake volumes.The exposure assessment uses common parameters for dose, average units of E. coli (CFU) ingested per month, the population ingesting fecal contamination and percentage of the population exposed.This allowed the generation of exposure estimates of fecal contamination for each exposure pathway in each cluster considering both adults and children.

Ethics statement
The implementation of this project has received several ethical approvals.Firstly, from the Universite ´Fe ´lix Houphoue ¨t Boigny Ethics and Deontology Committee (2020/CED/UFHB-N4 7) in the (S1 Text), the second one was the authorization provided by the municipal authorities (N˚399/MAB/SG) in the (S2 Text) and the third one is the authorization of the inspectorate of primary and preschool education (N˚278/2021/IEP/Ab-H) in the (S3 Text).Indeed, the ethical clearance for this study was obtained from the Universite ´Fe ´lix Houphoue ¨t Boigny Ethics and Deontology Committee (CED-UFHB) which has allowed the implementation of the field research.However, in addition to the CED-UFHB approval, an authorization was also provided by the authority of the city where the study was specifically taking place.During the data collection, informed consent was obtained from each participant before they were interviewed.Oral consent was preferred than written informed consent, because of the high level of illiteracy in the study area.Regarding the participation of the children, as well as the permission of the Inspectorate, we had the oral consent of the teachers and the pupils before the interviews.However, participation in the study was voluntary and participants could withdraw at any time without obligation.

Fecal contamination in the studied cluster in Abobo
The E. coli enumeration reveals the presence of E. coli in 90% (n = 108) of the samples.The highest concentrations were observed in the samples of soil, gullies and open drains (Table 2).
In Cluster I, characterized by unplanned and informal settlements, open drains exhibited the highest average concentration of E. coli (6 log CFU/ml) and the highest variability (standard deviation of 5.5 log CFU/ml).This trend was similarly observed in Cluster II, which comprises planned settlements, where open drains showed the highest mean E. coli value (6.1 log CFU/ml) and the highest standard deviation (5.6 log CFU/ml).
Conversely, the lowest concentration values were recorded in drinking water samples, with standard deviation values of 0.007 (Cluster I) and 0.005 (Cluster II), indicating a relatively stable and low level of E. coli contamination.

Behavior frequency
In municipality of Abobo, children represent the group with the most behavioral frequencies that led to contact with the exposure pathways in the different clusters (Figs 5 and 6).However, the frequency of behaviors was more pronounced for street food and gullies.Regarding the street food pathway, more than half of the children in both clusters reported having contact more than 10 times a week.The frequencies of these contacts were 81% in cluster I and 67% in cluster II.With regard to gullies, less than half of the children reported having contact 6 to 10

Risk profiles and people plots
Table 3 summarizes the global risk of exposure to fecal contamination in the two sampled clusters.However, soil sample results were not generated because the SaniPath tool does not include a behavioral question on the soil [14].
The highest risk of exposure (E) to fecal contamination was recorded in the street food samples of cluster I with values of 8.6 for adults and 9.2 for children.The lowest risks (E) were recorded in cluster II drinking water samples, with values of 1.4 for children and 1.5 for adults (Table 3).
The dominant pathways in cluster I were considered to be those with a risk value (E) ranging from 8.2 to 9.2 (Table 3).This concerns street food and gully for the children and adults in cluster I. Street food is a dominant pathway of exposure for children and adults with respective risks (E) values of 8.7 and 9.2.Gully water was identified as the dominant exposure pathway with a risk level (E) of 8.3 in children and 7.4 in adults.At the cluster II level, the maximum risk of exposure value (E) is 8.1.Table 3 presents gullies as the only dominant exposure pathway in this cluster with risk values of 7.1 and 8.1 for children and adults, respectively.
This section presents the results of the dominant pathways as a people plot with the different percentages of exposure and relative intake doses per month.Fig 7 shows the two dominant pathways (street food and gullies) of exposure to fecal contamination in the clusters.In cluster I, children (100%) are slightly more exposed to fecal contamination than adults (92%) for the street food pathway.In cluster II, regarding the gully water pathway, adults' average dose with 7.7 log CFU/month is low compared with children average dose (8.3 log CFU/ month).In terms of the average dose of dominant exposure pathways, the population living in cluster I were more exposed to fecal contamination than those in cluster II, with a maximum dose of 9.2 log CFU/month and 8.3 log CFU/month, respectively.
Regarding open drains, people in cluster I are more exposed than those in cluster II.As for stored drinking water and floodwater, adults in cluster II have the lowest exposure group compared to the other categories.Furthermore, adults and children living in cluster I have higher exposure averages for pathways such as gullies and street food.

Discussion
The high concentrations of E. coli detected in the samples from the different pathways indicate poor fecal management in Abobo, especially in on-site sanitation areas.In both clusters, gullies (surface water) represent the dominant pathway for adults (Cluster I/ E = 7.4; Cluster II/ E = 7.1) and for children (Cluster I/ E = 8.3; Cluster II/ E = 8.1) considering E. coli risk of exposure.During the transect walk, several gullies were observed throughout the clusters.Also, we could see that some households dump their wastewater in the streets that end up in the gullies.It is the same for toilet water and septic tank effluents.This behavior is the explanation for the high average concentrations of E. coli recorded from gully samples in cluster I (5.6 log CFU/mL) and cluster II (6 log CFU/mL), as well as the significant values of percentage of exposure (children cluster I: 100%) and of high doses (children in cluster I: 8.3 log CFU/month) in the cluster.Similar concentrations were found in wastewater from gullies in Yopougon, a neighborhood municipality with a significant presence of bacteria indicator of fecal contamination, in particular E. coli, in gully samples (6.4 log CFU/mL) [17] indicating the importance of fecal contamination in the District of Abidjan.The situation was pointed out by another study [25] which revealed that the reuse of urban wastewater and lagoon water caused an average annual risk of infection ranging from 90.07 to 99.9% for E. coli and from 9.42 to 34.78% for G. lamblia.Moreover, E. coli concentrations varied from 2.4 log to 3.4 log CFU/ mL in the drainage network and between 1.1 log and 2.2 log CFU/ mL in the lagoon [25].The author explains the presence of these fecal indicators by open defecation, as well as the dumping of household waste and wastewater in these areas.
Our study found street food is also a dominant exposure pathway, with a high level of risk of exposure in cluster I, especially among children (E = 9.2).The high risk among children could be explained by the sampling period, which took place during the school period when the children were away from home and ate street food (around the schools) where hygiene rules are not often respected.Most children are enrolled in schools, according to the policy of universal schooling, instituted by the government for all children from 6 to 16 years.Recent studies indicated that food is the dominant universal pathway.The food pathway has been shown to be the most common dominant pathway of exposure to fecal contamination in cities in low-and lower-middle-income countries [13].
This study has highlighted concentrations values ranged from 9.8 to 10.8 log CFU/serving in street food.This value is higher than that the concentration in our study.The possible explanation of this situation could be attributed to the sampling method.The study conducted in United States used serving-based estimation.
Furthermore, the street food exposure pathway is more important for children in cluster I with a risk (E) of 9.2.This situation could be explained by this study being carried out during the school period.During this period, most of the children eat from sellers located in the surroundings and/or in the school yard.However, these sellers do not really respect the hygienic conditions.Many studies have characterized street food sites as breeding grounds for rodents, insects, and flies that could promote the growth of microorganisms and increase the risk of food contamination and disease transmission [26].Also, the Centers for Disease Control and Prevention (CDC) estimated that more than 30% of gastroenteritis cases in low-and middleincome countries are related to foodborne transmission [27].Exposure studies in Bangladesh have also found high levels of microbial contamination, including coliform bacteria, in street foods, ranging from 5 log CFU/g in the beef burger to 6.3 log CFU/g in the sandwich [28].According to the government report, nearly 58% of the food sellers in Bangladesh did not cover their food and many did not wash their hands with soap during food preparation [28].A similar situation was observed in Accra (Ghana), where the risk of exposure was dominant among children under five years of age, independent of the standard of living.Indeed, in most markets in Accra, food is placed on dirty surfaces and collects dust contaminated with fecal matter.Also, the cultural context of Ghana means that the majority of food is traditionally consumed with the hands [29].However, Wang et al. found evidence of fecal contamination in hand washing samples, with E. coli concentrations that ranked from 2.25 to 5.2 log CFU/pair of hands [30].
The study found a higher exposure through gullies and open drains in the Cluster II despite the existence of infrastructure.This situation is attributed to poor infrastructure management on the one hand and the vicinity of poor areas near the middle-and high-income areas in other hand.In Abobo, each middle-and high-income area has surrounding poor areas with lack of sanitation facilities.In these poor areas, the waste collected is often discharged directly into drainage systems or open water bodies.Providing proper sanitation facilities could reduce the overall risk of exposure to fecal contamination [31].In addition, it is reported that climate change has repercussions on basic sanitation services and infrastructure [32].Since, extreme rainfall has been recorded in recent years in Abidjan [33], this situation could cause existing sanitation systems to overflow or break down, creating major health risks from pathogen and pollutant exposure during heavy storms [34].Thus, populations living in Cluster II neighborhoods should ensure that their infrastructure is properly managed to avoid or limit the risk of exposure to certain pathways.
Regarding drinking water, the majority of households living in the neighborhoods of the two clusters consumed stored drinking water.This water was not identified as a dominant exposure pathway because the drinking water samples had low concentrations of E. coli, ranging from 0 to 0.024 CFU/ml.This conclusion is supported by the relatively low standard deviation values observed in both clusters (0.007 CFU/ml for Cluster I and 0.005 CFU/ml for Cluster II).Nonetheless, it is worth noting that the detection of some E. coli in the drinking water samples may be attributed to the unsafe and/or uncovered containers practices [35].Indeed, many households reported storing water for consumption during the behavioral survey.Despite the program "Water for All" initiated by the Ivorian government since 2020, some populations living in informal settlements are still not connected to the drinking water network.These people buy their water from water sellers and store it in containers without respecting the hygiene requirements.Also, the practice of storing water could be explained by the recurrent blackouts that the city of Abidjan experienced during the period from March to June 2021, mainly in the municipalities of Yopougon, Abobo and Cocody.This situation is not specific to Abobo or Sub-Saharan African urban areas.A study conducted in the city of Dhaka (Bangladesh), revealed relatively high levels of E. coli (3.20 log10 MPN/100 mL) in municipal drinking water [36].The author justifies these results by frequent pipe breaks, illegal connections, and low water pressure due to intermittent service [37,38].In contrast to these findings, studies by Ronoh and al. in Uganda showed that drinking water was free of E. coli throughout the year [36].In fact, 70% of the population uses water supplied by the National Water and Sewerage Corporation (NWSC).However, these households treat the water before drinking by either boiling or chlorinating it [36].This practice is not common in the municipality of Abobo, where most people do not treat the water supplied by National Water Company (SODECI) before drinking it.Moreover, Wright et al. found that contamination of drinking water stored in households is related to the cleanliness of the containers [39].
Previous studies at national level have shown E. coli to be the most prevalent fecal indicator in the environment.Indeed, according to the work of Becker et al., this fecal indicator is responsible for 32% of the confirmed cases of patients with persistent diarrhea [40].

Conclusion
Poor management of fecal sludge is a common practice in low-income neighborhoods of Abobo Municipality.The SaniPath tool was used in this study to identify the different exposure pathways of fecal contamination, which residents of the informal settlements in Abobo face.This study reveals the presence of the fecal indicator E. coli in 90% of the samples collected in the different neighborhoods of the municipality.Street food and gully are the dominant exposure pathways for children and adults in cluster I (low-income neighborhoods).However, in cluster II (medium and high-income neighborhoods), the gully is the only dominant exposure pathway.Despite the existing Municipal Ordinance from 03.08.2018 on police regulations for on-site sanitation, the risk of exposure to fecal contamination remains high in cluster 1. Systematic control of sludge storage facilities and better supervision of street food vendors should be explored by the municipal authorities as strategies to prevent fecal contamination.Also, implementation of an inclusive sanitation system approach at the municipal level could considerably reduce these sources of contamination.Future equitable intervention strategies must consider the socio-economic inequalities across the different neighborhoods and provide targeted interventions for exposure areas.Therefore, policymakers, NGOs, and the private sector should provide access to reliable sanitation to all households, regardless of their socioeconomic status, to prevent epidemic risks in urban areas.

Table 2 . E. coli concentration in the various pathways per cluster.
Fig 5. A. Frequencies of food behaviors in cluster I. B. Frequencies of food behaviors in cluster II.https://doi.org/10.1371/journal.pwat.0000074.g005timesper month.The frequency was 48% in Cluster I, while in Cluster II only a small proportion (16%) reported having this kind of contact.

Children Adults Children Adults Children Adults Children Adults Children Adults Children Adults
*Dominant pathways in cluster I/ **Dominant pathways in cluster II https://doi.org/10.1371/journal.pwat.0000074.t003