Socio-Environmental Signatures of Cholera Epidemics in Douala - Cameroon

An assessment of community vulnerability and recommendations for effective response

by Mr. Anthony Banyouko Ndah (Author) Suinyuy Derrick Ngoran (Author)

Scientific Study 2018 25 Pages

Medicine - Public Health



This study is an inquiry into the socio-epidemiological characteristics of sections of the Douala municipal metropolis in Cameroon in the face of recurrent and increasingly large cholera outbreaks in Cameroon. The purpose is to provide vital insights into the extent and nature of vulnerability of the populations to cholera outbreaks, as well as provide a leeway for the effective identification of maximum risk areas and vulnerable populations so as to tailor limited response resources efficiently and effectively. The study establishes the following:1). Contrary to the popular belief that in a cholera-endemic setting, the greatest burden is in the younger age groups (0-2 and 3-9), in the case of Douala, based on data of the last three epidemiological periods (2010, 2011 and 2012), the young adult / adult age groups (21-30 and 31–40 years) have been identified as the most vulnerable. 2). Concerning gender, males have been found to be far more vulnerable than females; 3). Social characteristics not commonly considered in public health strategies, including attitudes towards hygiene and sanitation, limited knowledge of diseases and cholera transmission mechanisms, as well as magico-religious beliefs on the origins of cholera, are possibly the dominant causes of high vulnerability to cholera and/or serve as major hindrances to effective mitigation; 4). Cholera risk factors such as slum settlements, lack of proper social amenities and services, for example, potable water, drainage, waste collection, hygiene and sanitation facilities, are generally spread throughout the Littoral Region and Douala in particular, though characterized by glaring unevenness constitute important risk facts but not direct causes of high vulnerability. Though there appears to be a direct relationship between the existence of risk factors and vulnerability, human attitudes and beliefs are the bridge linking these two concepts. Finally, an Integrated Cholera Management (ICM) framework has been proposed. This framework is intended to show the interconnected components of an ideal cholera management system in Cameroon.


Cholera is a bacterial disease caused by Vibrio cholerae, which has been found to be native to coastal ecosystems.Vibrios, including V. cholerae, can be found in virtually any coastal water body, especially in the tropics and subtropics (Lipp et al. 2002). The virus is spread by fecal-oral transmission and causes a range of disease from asymptomatic or subclinical infection to severe dehydrating diarrhoea that can cause death within 6-12 hours, a limited period of time during which patients can lose more than 10% of their body weight in fluid losses, and adults can lose 20 litres or more (Weil 2012).

1.1. The state of global cholera epidemiology

The disease is believed to occur in epidemic proportions and become endemic in areas of the world where the 20th century innovations of clean water and latrine use are not yet realized such as in the poor parts of Southeast Asia especially in the Ganges Delta where 3-5 million cases are recorded each year (Weil 2012), as well as in Africa. Cholera is indeed a global health catastrophe, though the brunt of epidemic events and impacts are borne more by poor developing countries. Even in the poor countries, the disease affects different segments of population differentially, imposing a form of epidemiological segregation built along lines of poverty and social wellbeing. In Africa, a recent online article by Nossiter(2012)reported that a fierce cholera epidemic is spreading through the coastal slums of West Africa, killing hundreds and sickening many more in one of the worst regional outbreaks in years, made worse by an exceptionally heavy rainy season that flooded the sprawling shantytowns in Freetown and Conakry, the capitals of Sierra Leone and neighbouring Guinea. The same article goes further to point out that in both countries, about two-thirds of the population lack toilets, a potentially lethal threat in the rainy season because of the contamination of the water supply. In Asia, the case of Bangladesh in particular has received much media attention. Being reputed as the most densely populated country in the world, the capital city Dhaka is home to at least 15 million residents, most of who live in urban slums. Weil (2012) makes allusion to the fact that the great majority of cholera patients come from the urban slums, particularly Mirpur Slum and the major causes of cholera endemicity have been identified as: manipulation of water pipes through illegal piping which leads to sewage mixing with the water supply, failure by most people to boil or treat their water prior to usage, and the general belief that in Dhaka, diarrhea is a common and somewhat normalized fact of life. In yet another study by Sur et al. (2005), in Kolkata, the third largest city in India and one of the world’s most densely populated cities, cholera remains a persistent scourge in the communityof slum dwellers. The authors note that the study site, 0.7 square kilometres in size, was already in maps from 1856 as an impoverished residential area known as Narkeldanga, which encompasses what is known today as bustees, legally recognized and registered slums, characterized by narrow streets with little space between houses, intermittent piped municipal water supply shared by several households, one or two latrines and water taps, sewage collected in open gutters which overflow when it rains (Sur et al. 2005). An earlier study in cholera-endemic Bangladesh from 1966 to 1980 found out that cholera isage selective, most common between 5 and 9 years of age followed by children 1–5 years (Glass et al.1982); however, Sur et al. (2005) caution that despite this selectivity, no age groups is spared during a cholera outbreak, though the very young suffer most.Theprecise mechanisms and environmental interactions that give rise to increased numbers of Vibrio cholerae in an aquatic environment have yet to be fully understood, and this is coupled with the fact that it is not yet possible to construct mechanistic models for prediction of their presence and abundance with exquisite accuracy (Constantin de Magny et al. 2010). However, innovative studies in the field demonstrate how closely cholera is tied to environmental and hydrological factors and to weather patterns — all of which may lead to more frequent cholera outbreaks as the world warms (Lipp et al. 2002). As early as 1975, Kaneko et al. identified temperatures in the range of 25° to 30°C as well as favourable salinity levels of about 15‰ and the bloom of algae (copepods) to which have a positive effect on attachment of V. cholera as favourable conditions for cholera emergence (Kaneko et al. 1975). Following in this direction, recent statistical models presented in a study by Louis et al (2003)provide a valuable understanding of the large-scale processes that dominate the ecology of V.cholerae by showing that seasonal pattern of occurrence of V. cholera was correlated with higher temperatures, indicating that there is a temperature threshold between 17 and 19°C, and the frequency of occurrence of V. cholerae is significantly greater at temperatures above 19°C and lower salinity levels between 2 and 14ppt, the optimal salinity being between 2 and 8 to 10ppt (Louis et al. 2003). Therefore, if Vibrio cholera is a free living occupant of aquatic environments, why then are some areas experiencing severe epidemic outbreaks year in year out, where as others record just a few cases from time to time? With this question in mind, while much research has focused on enhancing understanding of the environmental and ecological mechanisms which favour the thriving of the cholera-causing bacteria, social factors and attitudes in cholera endemic areas, which may contribute to high or low exposure of people to the deadly disease need equal consideration. Therefore, a sociological study of the attitudes and beliefs of people inhabiting an endemic zone can open a window into the vulnerability situation of the populations, as well as direct short term preventive measures which also save lives prior to the development of long term predictive and eradicative measures.

1.2. The State of Cholera epidemiology in Douala, Cameroon

Cholera in the Littoral Region of Cameroon, precisely in the city of Douala has become not just a public health crisis but a humanitarian disaster as well. Douala, the economic capital of Cameroon, located in the coastal plain of the Wouri Estuary on the Atlantic Ocean, also doubles as the capital of the Littoral Region is especially hard-hit. Infectious, emergent and re-emergent diseases have become important components in the medical vocabulary of the Littoral Region of Cameroon since recent times. Most of these diseases are related to water or the poor management of the water environment in Douala, and classified as very high degree of risk. Some of the most common include:food or waterborne diseases: bacterial and protozoan diarrhea, hepatitis A and E, and typhoid fever; vector-borne diseases: malaria and yellow fever; water contact disease: schistosomiasis; respiratory disease: meningococcal meningitis etc. The health situation in this area has therefore exceeded a normal public health challenge and can rightly be classified as a humanitarian crisis, given the frequent of yearly outbreaks. Of all the diseases listed on Table 1, Cholera and Malaria are the most dramatic and major causes of death, and therefore of greatest concern. But unlike malaria, a more silent health issue, which is known to be caused by the female anopheles mosquito, cholera is multi-causal and thus highly complex, characterised by spectacular outbreaks.

Table1. Summary of some major diseases in the Littoral Region (2010 – 2011 )

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Note: the data was obtained from the Regional Delegation of Public Health, Douala in February 2011(Ndah,2011)

Cholera however stands out in the region which is endemic for the deadly bacterial infection since the arrival of the 7th pandemic of cholera in the Gulf of Guinea (Wouafo et al. 2007), with recorded epidemic outbreaks dating from 1971 through to present (Guévart et al. 2006; 2010). Outbreaks were observed to be occurring approximately after every two or three years during the dry season (Garrigue et al, 1986). Recent national trends point to a higher frequency of occurrence, with ever fluctuatingmortality rates among the afflicted populations (Figure1).According to the Regional Delegation of Public Health, a total of 28 major epidemics have been recorded in Douala alone; the most deadly being those of 1971, 1983, 1991, 1996, 1998, 2004, 2005, 2010, 2011, with over a thousand cases each (Fouda, 2012). A major outbreak was experienced in January 2004 and during which approximately 2924 cases and 46 deaths were reported in Cameroon from the 1st of January to the 9th of June 2004.In Douala, more than 500 cases of cholera werereported within seven weeks of the onset of the pandemic, leaving at least 13 people dead (Njoh, 2010; Littoral Regional Delegation of Public Health, 2011). By the time the disease subsided, 6000 persons were reported infected and hundreds dead[1]. However, a lot of inconsistency remains in the data from different sources. During the short rainy season of March and April of the 2010 epidemiological year, cholera peaked with an average of 120 cases per week, followed by a number of peaks and troughs, and by September to mid-October the number of cases increased to more than 400 cases per weekin Douala, according to the Littoral Regional Delegation of Public Health, in 2012.There was a sudden resurgence of the epidemic in Littoral region, particularly in Douala and the surrounding localities, with over 430 cases a week, in 2011 and by the 44th week of 2011, a cumulative 3,792 cases and 77 deaths were registered in Douala alone (International Federation of Red Cross and Red Crescent Societies 2012). Official figures however place the total number of cases in Douala at a staggering 5,463 reported cases between January and December 2011 with a case fatality rate of 1.92% (Littoral Regional Delegation of Public Health, 2012). By the 11th week of 2012, in the month of March, the Littoral Regional Delegation of Public Health officially reported 33 cases with a case fatality rate of 3.03%.The situation is presented in Figure 1 and Table 2 below. It is therefore clear that Cameroon in general and Douala in particular, like other regions of cholera endemicity, the disease does not disappear after an epidemic peak but returns in successive waves making it of great relevance the need to identify environmental or climate factors that may promote epidemics, thereby enhancing understanding of the dynamics of the disease.Thus, it becomes imperative to provide answers to the following questions: what causes periodic oscillations in cholera outbreaks, and why are some areas more prone to endemism? (Lipp et al., 2002). Some studies have attempted to establish the underlying causes of cholera endemicity in Douala. Guévart et al. (2006) have provided a comprehensive description of the environmental factors contributing to cholera endemicity in Douala. The natural location of Douala in the Cameroon estuary, an environment characterized by poor water circulation due to its low-lying nature, as well as high demographic and socio-economic pressures; the sandy clay soils which are poorly consolidated and facilitates the contamination of ground water; shallow dirty polluted foul-smelling groundwater; the presence of vast expanses of swamps, streams or drainage ditches, infested with Algae; high temperatures, with low rainfall and drought during certain periods of the year, (Guévart et al., 2006) have cumulatively subjected Douala into a cholera endemic zone. Tatah et al. (2012), in a localized study in the Bepanda area, found out that 27.4% of the water samples were contaminated, with high isolation rates being obtained from streams (52.4%) and wells (29.8%). The number of isolates was significantly higher (P < 0.05) in the rainy season (35.5%), 23 (24%) O1 serogroup isolates were detected in streams and wells, whilst 64 (66.6%) were non-O1/non-O139, thus concluding that water sources, poor hygiene and sanitation were a major reservoir and cause of cholera endemicity in the area, as well as climatic influences (temperature and salinity).

Table 2. Total cases and deaths from cholera in the Littoral Regionbetween 1996 and 2005

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Note: Cases notified to the World Health Organization (a dapted from WHO 2004)

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Figure 1: WHO-notified Cholera cases and deaths in Cameroon between 1996 and 2005

Similarly, a prospective study to investigate the extent of pollution and assess the scope of potential bacterial pathogens in the Douala lagoon has led to the finding that indiscriminate disposal of untreated wastes which are often heavily laden with sewage and the presence of potential bacterial agents such as Bacteroidesfragilis, Pseudomonas aeruginosa, Aeromonashydrophila, Klebsiellapneumoniae and E. coli in the Douala lagoon may pose a serious threat to the health and well being of users of the Lagoon (Tatah et al. 2008). This may constitute another potent cause of cholera epidemics in Douala. The important contribution of climatic variables such as temperature and associated changes in salinity, in the evolution and spread of cholera epidemics in Douala, have also been noted (Guévart et al., 2006; Tatah et al. 2012). The seasonality of cholera outbreaks also proves the point that climatic factors play a big role in the epidemicity and endemicity of the disease in Douala (Guévart et al. 2006). Characteristics specific to the city of Douala have also been identified as contributing to the frequent cholera outbreaks in the area. Most outbreaks begin in Bepanda, a slum built on a garbage dump in a swampy zone in the city of Douala; anovercrowded residential area which is as a result of uncontrolled urbanization (Njoh2010), with a population of about 11,000 people, who live without adequate access to clean water or basic sanitation facilities (Njoh 2010; Littoral Regional Delegation of Health 2011). Infrastructural lapses such as the absence of a good drainage or sewage disposal system in Douala, as well as the fact that the 8,000 wells in Douala (about 98% of all wells) are not protected and are located near latrines which definitely drain into them, have also been noted to constitute major risk factors, according to the head of mission of Medecins Sans Frontiers (MSF) in Cameroon, Max Antoine Grolleron (IRIN News, 2004)[2]. Shallowdrains which pervade the entire city function as pathogen reservoirs and the use of water from these reservoirs for any household activity are the most important risk factors that influence the spatial distribution of cholera in Douala (Guévart et al. 2006).

In previous studies, attempts to establish the causes of cholera epidemics in Douala have the general conclusion that coupled with its endemism in the area, economic poverty and poor living conditions, as well as the contamination of water systems with faecal matter and cholera-causing bacteriaare responsible for frequent outbreaks (Tatah et al. 2012; Peng et al. 2011; Fogwe&Ndifor 2010; Wouafo et al. 2007; Eneke-Takem et al. 2009). With this idea in mind, and with no solution to the poverty issue in the slum-infested city in the foreseeable future, public health authorities have resorted to the only reasonable course of action available to them based on the narrow techno-centric perspective common with medical practice – that is ‘wait for the epidemic to strike and intervene with medication and awareness campaigns. In the management of the disease, a mirage of hope often clung upon by Cameroonian public health authorities as a measure of success in the fight against cholera is that the case fatality rate (CFR) of cholera, though still relatively high and constantly fluctuating, has been greatly reduced despite the skyrocketing number of cases in recent years (Figure 1). This has been attributed to the timely medical interventions during outbreaks, as well as free medical attention and treatment provided by health authorities. The primary treatment is rehydration, and in most patients oral rehydration is sufficient. In cases accompanied by severe vomiting, or dehydration that progresses to depressed consciousness, intravenous rehydration is required, while antibiotic treatment decreases the severity of disease and shortens the duration of symptoms (Weil 2012). This may however not last longer as the CFR risk increasing again with evidence of current resistance of the Vibrio cholerae to drugs.In a study by Garrigue et al. (1986) on the massive and systematic use of chemoprophylaxis which began in April 1983, it is revealed that during the 1984-1985 epidemic, 89.3% of the isolated strains were resistant to sulphamides, 87.5% to a sulfamethoxazole-trimethoprim combination and to the 0/129 disk, 55.3% to tetracycline, 91.1% to chloramphenicol, 73.2% to streptomycin and 94.6% to ampicillin. Unfortunately, these drugs have remained the major remedy used by medical authorities to combat outbreaks of cholera. Social issues stand prominent among the barriers to cholera prevention and control, leading to misinterpretations and misconceptions, especially during outbreaks in cholera-endemic regions. In the attempt to establish the underlying causes of high vulnerability of the populations of Douala to cholera, some studies have deviated from the focus on social infrastructural and environmental risk factors, and have cited social behavioural factors such as individual characteristics, societal norms and sources of health educational messages (Njoh 2010) as well as the reformation of urban tribes and persistence of traditional attitudes toward waste disposal and water use, which have not only led to high-risk behaviour but also created barriers to sanitation and hygiene (Wouafo et al. 2007). These however have unfortunately not been investigated intensively investigated and form the object of the present study. In this second edition, two major changes and updates have been made: firstly, the quality of maps and graphs have been improved. The maps have been re-made using GIS software METEOINFO. Secondly, a section on Integrated Cholera Management (ICM) has been added to the discussion.


2.1. The Study area: The Douala sedimentary basin located in the Littoral Region of Cameroon, precisely in Wouri Division and has as major physical feature the Cameroon Estuary (Figure 2).

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Figure 2. Map of the Littoral Region of Cameroon showing the Wouri Estuary

Geographically, Douala is located at latitude 4 1´ North and longitude 9 45´ East and covers a surface area of about 886 km²(Douala Urban Council 2011). This city of about 3.5 million inhabitants today, displays anucleated settlement pattern (Nkem 2008), constituting the built-up area as well as the marine and coastal space is administered under the Wouri Division of the Littoral region of Cameroon.

The Douala municipal area has grown on a typical marine and coastal space where the old barrier islands were colonised by the Bonanjo, Akwa, Deido, BepandaBassa, Bonamoussadi and the Bonaberi districts, which today support high population densities (Asangwe, 2006). Today, six sub-divisions make up Douala’s administrative setup, each administered by a mayor, under the authority of a Divisional Officer, while a Governmental Delegate governs the metropolitan area under the Urban Council. Presently five of the six sub-divisions, which make up the Wouri Division are considered as strictly within the urban council and thus fall under the influence of the Government Delegate; areas whose jurisdiction is also claimed by the Divisional Officer (Douala Urban Council 2011), creating an avenue for conflicts of authority which strongly reflects in the poor management of the city. In addition to administrative lapses, the Douala area has the crucial problem of abundant aquatic terrain in the face of scarcity of land, which poses a serious challenge to coastal zone management, leading to environmental degradation as a result of the pursuit of urban spatial growth (Asangwe 2006).

Table 3. Subdivisions which makeup Douala in Wouri Division, Littoral Region of Cameroon and the major quarters

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Note: data obtained from Douala Urban Council (Ndah, 2011)

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[1] Posted online by Dickson Njoke on Monday, 20 September 2010. Available on: http://newconceptsounds.com/2011/03/20/douala-ii-campaign-against-cholera/ accessed on 02/2011

[2] www.irinnews.org/report.asp?reportID=39664 posted on 24 Feb 2004. Accessed on 02/2011


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socio-environmental signatures cholera epidemics Douala Cameroon




Title: Socio-Environmental Signatures of Cholera Epidemics in Douala - Cameroon