This research applied an integrated assessment to understand how environmental risk factors (e.g. sanitation infrastructure access, and rodents) influenced flood-related waterborne disease transmission in two municipalities (Abobo and Cocody) in Abidjan, Côte d’Ivoire. We found that among the identified risk factors to disease transmission in the study area, poor access to sanitation infrastructure and open defecation are the most important. Furthermore, we showed that, though V. cholerae and Leptospirosis diseases were not identified in our study, the presence of rodents in the housing environment, and poor sanitation including open defecation practices could increase disease transmission risks. This investigation provides reliable knowledge on the status of flood-related exposure to V. cholerae and Leptospirosis and G. lamblia infections and associated environmental risk factors in Abidjan.
Knowledge and experience on flooding risk in the study area
Globally (49%) of the participants reported to having knowledge and experience about flooding risks causing temporal migrations more often. In the city of Abidjan for some decades, flood-affected populations due to many reasons including geographical locations climate variabilities, causing severe damage to infrastructure, and human loss. The critical issue of addressing flooding risk and associated negative impacts are not specific to Abidjan. Indeed, recent statistics show that floods have affected 2.3 billion people worldwide in the last 20 years and are associated with a wide range of negative health outcomes (Suhr & Steinert, 2022). A recent study confirmed that local knowledge of flooding by communities could contribute to providing a better understanding of flood vulnerability and assist in developing adaptive measures to increase people's resilience (Membele, Naidu, & Mutanga, 2022). A meta-analysis of West Africa flood perception literature reveals that, despite the experience of a devastating flood in 2009 in Burkina Faso, there is still the need of developing a practical flood risk management plan (Schlef, Kaboré, Karambiri, Yang, & Brown, 2018).
Understanding causative factors leading to health exposure associated with flooding risk
The households affected by floods in the study area are statistically significant for the following socio-economic variables, namely the access to sewerage system and septic tanks and residential habitats. This result could be explained by flooding during this last decade in Abidjan, which severely damaged infrastructure and caused human loss in some municipalities (e.g. Cocody, Yopougon, Attécoubé, and Abobo), landsides, and the overflow of open drainage infrastructures. In the municipalities of Abidjan, floods are linked to habitats located in storm basins, runoff, the over flow of rain in drainage networks, and the presence of solid waste in drainage, blocking the normal flow of raining water (Rother et al., 2020). This description of flooding impacts is not specific to Abidjan, because it can affect populations with different socio-economic and cultural characteristics depending on other anthropogenic factors, such as poor urbanization, the efficiency and resilience of sanitation infrastructure, and uncontrolled climate adaptation. A study showed that flooding is among of the natural critical hazards leading to catastrophic impacts on society and urban infrastructure worldwide (Qi, Ma, Xu, Zhao, & Chen, 2022).
The analysis of health risk factors during flooding events revealed that even in the low range (range from 0.5 - 3.4%), open defecation practices contributed to an increase in waterborne disease transmission through runoff. In addition, urination is very common in surrounding neighbourhoods. Indeed, around half of the households used septic tanks, while one-third used latrines, and the remaining part go for open defecation practices and sewerage. Similar findings were reported from other settings facing flooding problems, and the authors showed that interventions on sanitation, waste management, and adequate storm drainage are necessary for developing responses to flooding risk (Mansur, Brondizio, Roy, de Miranda Araújo Soares, & Newton, 2018). Furthermore, access to reliable sanitation infrastructure is challenging in sub-Saharan African countries. For example, in Ghana where the population faces floods every year, a study has recommended the construction of modern city-wide sewerage systems to cope with the rainfall patterns (Owusu-Ansah, 2016). The problem of sanitation infrastructure in flooding occurrences is, therefore, not specific to Côte d’Ivoire.
A secure access to sanitation infrastructure could influence the transmission of flood-related waterborne diseases in the cities of Côte d’Ivoire. Yet, there is a lack of investigation addressing flood-related diseases in Côte d’Ivoire. There have been studies conducted that analysed the necessity of sanitation improvement for reducing waterborne disease risks in the context of wastewater reuse or drinking water at school (Parfait K Kouamé et al., 2014; Parfait K. Kouamé et al., 2021). The same limitations were confirmed in Senegal through a comparing pre-and post-intervention activities showing the importance of water, sanitation and hygiene access as the main drivers to reduce disease risks at household levels. Additionally, the increase of resilience mechanisms combined with adequate sanitation services are necessary to cope with health risks regarding floods. This point of view is highlighted by a recent study showing that the surveillance of floods is essential for areas where disease clusters have already been highlighted, specifically for diarrheal diseases, cholera, hepatitis leptospirosis, and malaria (Kakalou & Tsiamis, 2021).
Flood-related waterborne disease transmission patterns
Our investigation revealed also that malaria infection is high (61%) in households during flooding events in the study area. In terms of symptoms observed by participants, fever, vomiting, diarrhoea, and miscarriage were noticed. Flooding water can indirectly cause malaria and diarrhoea. Particularly, diarrhoea symptoms could be associated with malaria or other diseases, such as cholera. There is not a specific plan to address the issues of malaria and diarrhoea transmission in Côte d’Ivoire, specifically for Abidjan, associated with flooding occurrences. Therefore, a study conducted in the northern part of Côte d’Ivoire showed that the strong seasonality of climate variables (10 mm of monthly precipitation) increases the number of clinical malaria episodes (M’Bra et al., 2018). Malaria infections are a broad concern in West Africa, because a recent study showed that seasonal malaria transmission is associated with the latitudinal variation of the rainfall, and the southern area of West Africa is at-risk of malaria epidemics (Diouf et al., 2022). Furthermore, this study in Abidjan showed that open defecation practices were reported despite the low percentage of open defecation reported in our study, and the effects of open defecation are figuring high globally. These practices depend on the waste management system (e.g. open dumping or not) and could increase the occurrence of microbiological contaminants through runoffs. A similar study conducted in Ethiopia has revealed that open defecations had higher numbers of hookworm eggs in stool. These could be a source of exposure during flooding events, as is the case in Abobo and Cocody municipalities. Worldwide, open defecation affects 1 billion of people, with 842,000 annual deaths due to sanitation-related diseases (Prüss-Ustün et al., 2019). For instance, authors showed the probability of hookworm infections in flooding events are high (Anegagrie et al., 2021). In Ghana, flooding caused the displacement of people and placed them at high risk of contracting diseases, such as cholera, malaria and hepatitis (Mensah & Ahadzie 2020).
Furthermore, the current study revealed the presence of G. lamblia cysts in flooding water in the Abobo municipality, with lower concentration of oxygen concentration (0.05 - 0.16 mg/l). The presence of G. lamblia in rainwater is an indicator of poor microbiological quality, and the potential exposure to diseases. G. lamblia in rainwater in Abobo could be associated with the poor sanitation conditions in this setting during the rainy seasons. The municipality of Abobo is characterized by the poor collection of solid wastes, the absence of the waste recycling infrastructures, and the lack of wastewater treatment facilities. Similar studies that have been conducted in other contexts revealed the occurrence of G. lamblia in rainwater, such as in Abobo municipality. For example, in Pakistan, pathogens, such as G. lamblia and Cryptosporidium, are known as faecal contamination indicators (Khan et al., 2021). In most sub-Saharan African countries, many factors are involved in the transmission of G. lamblia, due to open defecation and poor faecal sludge management. Indeed, Giardia is the foremost cause of parasitic infection in the USA with an estimated 1.2 million cases and 3581 reported hospitalizations annually (Kumar et al., 2020). A study conducted in Vietnam revealed that floodwater posed public health risks in urban setting, due to the presence of enteric pathogens (Huynh, Nguyen, Vinh, Baker, & Pathirana, 2019). Additionally, it was reported that poor individuals have unequal opportunities to cope with the shocks from flooding, where they are deprived access to water services more than wealthier households, as observed in the Abobo locality (Grasham, Korzenevica, & Charles, 2019).
Our study cannot exclusively show the link between the occurrence of G. lamblia and the effect of climate variabilities. However, floods caused by climate variabilities combined with the poor infrastructure quality in Abidjan and runoff of water are likely to influence the dynamic of pathogens.
Environmental sanitation and flood-related zoonotic risk
The results revealed three species of rodents in the study area: Mus musculus, Crocidura, and Rattus. The biomolecular analyses conducted on the blood and urine of rodents using PCR showed that there is no contamination of rodents capable of transferring Leptospirosis disease in both municipalities. There is an increased awareness that rodents in urban settings, as a reservoir of pathogens, affect emerging disease transmission patterns in the human environment. Furthermore, the occurrence of the recent SARS-CoV-2 could be an example of the critical issue regarding the contact between humans and animals (Chauha, Dessie, Noreddi, & Zowalaty, 2020). Rodents represent the largest order of mammals (40%), with 2000 species of this order (Krijger, 2020). Terrestrial mammals are scarce, therefore, there are at least four genera of rodents: Acomys, Gerbilliscus, Lemniscomys, and Mastomys (Manthi & Winkler, 2020). These animals can be potential risk factors through poor sanitation and their contact with households, as observed in Abobo and Cocody municipalities. Similarly, a study showed that rodent reservoirs are associated with the poor management of solid wastes in Kenya (Krystosik et al., 2020). Climate change requires the sustainable management of solid waste management to prevent diseases. In Kuala Lumpur (Malaysia), authors showed the association between rodent distribution and disease transmission, and the change in climate conditions (Mackenzie & Williams, 2009; Naing, Reid, Aye, Htet, & Ambu, 2019). This correlation was also highlighted in a study conducted in the United States of America about rodent borne disease occurrences (Anstead, 2021). Other studies reported on the effect of meteorological conditions on rodent population dynamics and transmission by Rattus rattus sp. transmission, which increased during the period El-Nino, and from heavy rainfall found, as observed in Abidjan (Ambu, 2014). In West Africa, particularly in Nigeria, Lassa fever caused by rodent borne viral hemorrhagic fever was observed, and the authors showed that this pathogen is sensitive to population dynamics, rainfall, and flooded agricultural activities (Zhao, Musa, Fu, He, & Qin, 2020). In British India, similar observations were made, showing that when the relative humidity levels are high, outbreaks in rodents were increased in parallel (Tennant, Tildesley, Spencer, & Keeling, 2020). Although the biomolecular analyses carried out on rodent blood and urine were negative on flooding water contamination by Leptospira spp. in Abobo and Cocody municipalities, our investigation indicates the importance of further research to increase awareness and in-depth investigation of zoonoses transmitted by rodents in flooded urban environments in sub-Saharan Africa.
Strengths and limitations
This investigation is one of the first address the transmission patterns of flood-related waterborne diseases in Côte d’Ivoire. This study also has several limitations. Shortcomings in the questionnaire framing and the sampling method could lead to some indirect biases on the results. Firstly, the survey was only conducted in settings experiencing flooding events, in order to gather accurate data. Therefore, this process of having no control sites was a major limitation in the study. Secondly, the questionnaire did not have questions related to Leptospirosis as a disease because the participants have no clear idea about it. Thirdly, the sampling of rodents was carried out with traps at household level and not outside houses, in open drainage systems and open waste dumping sites. Rodents from the outside environment are more in contact with contaminants and pathogens from wastes than those in households. This limitation could explain the absence of the Leptospira vector in rodent blood and urine. Additional limitations were human urine as risk factors and the dilution effect of the flooding water.