Socio-environmental signatures of cholera epidemics in Douala - Cameroon and community vulnerability assessment

1. INTRODUCTION

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 cholera-causing bacteria is spread by faecal-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 in which patients can lose more than 10% of their body weight in fluid losses, and adults can lose 20 litres or more (Weil 2012). Cholera is indeed a global health catastrophe, though the brunt of epidemic events and impacts are borne more by poor developing countries. 3 to 5 million cases are registered each year, mostly in poor parts of Southeast Asia, especially in the Ganges Delta, and was previously 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 (Weil 2012). Even in poor countries, the disease as has been observed to affect different segments of population differently, imposing a form of epidemiological segregation built along lines of poverty and social wellbeing. In Afrrica, a recent online article by Nossiter (2012) reported a fierce cholera epidemic 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 neighboring Guinea. The role of meteorological factors in the spread of the disease is also highlighted here. 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 countries 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 comes 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, diarrhoea is a common and somewhat normalized fact of life. This denotes clearly the distinction between risk and vulnerability factors. In yet another study by Sur et al. in Kolkata, the third largest city in India and one of the world’s most densely populated, cholera remains a persistent scourge in the community of 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 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 is age 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 an outbreak, though the very young suffer most. The precise 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) 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 the 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 14 ppt; the optimal salinity being between 2 and 8 to 10 ppt (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 vulnerable situation of the populations as well as provide opportunities for preventive measures which save lives prior to the development of long term predictive and eradicative measures.

1.1 Review of the status of Cholera in Douala

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. 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 diarrhoea, hepatitis A and E, and typhoid fever); vector-borne diseases (malaria and yellow fever); water contact disease (schistosomiasis; respiratory disease); meningococcal meningitis, etc. The human 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 and number of casualties. Of all the diseases listed in 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. Given the figures, cholera has a far greater case fatality rate (CFR).

Table 1: Summary of some major diseases in the Littoral Region between 2010 - 2011

illustration not visible in this excerpt

Source: Ndah, 2011; data from the Regional Delegation of Public Health, Douala, Feb. 2011

Cholera therefore 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). In the early periods of cholera emergence, 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 fluctuating mortality 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). The major outbreak of January 2004 resulted in approximately 2924 cases and 46 deaths in Cameroon from the 1st of January to the 9th of June 2004. In Douala, more than 500 cases were reported 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 week in Douala (Littoral Regional Delegation of Public Health 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 placed the total number of reported cases in Douala at a staggering 5,463 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.

illustration not visible in this excerpt

Figure 1: WHO-notified Cholera cases and deaths in Cameroon between 1971 and 2011 (WHO, 2012)

Table 2: No. of cholera cases and resulting deaths in Cameroon, notified to WHO between 1996 and 2005

illustration not visible in this excerpt

Source: Ndah 2011; adapted from WHO 2004

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 made significant advances in establishing the underlying causes of cholera endemicity in Douala. Guévart et al. have provided a comprehensive description of the environmental factors contributing to cholera endemicity in Douala. In their study, 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 in Douala, found out that 27.4% of the water samples were contaminated the cholera-causing bacteria, with high isolation rates obtained from streams (52.4%) and wells (29.8%). The number of isolates was also 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. They conclude 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).

Similarly, a prospective study to investigate the extent of pollution and assess the scope of potential bacterial pathogens in the Douala lagoon 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 Bacteroides fragilis, Pseudomonas aeruginosa, Aeromonas hydrophila, Klebsiella pneumoniae and E. coli in the Douala lagoon 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.

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 therefore 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]. Shallow drains 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).

These points probably explain why most outbreaks begin in Bepanda, an overcrowded residential slum built on a garbage dump in a swampy zone in the city of Douala; a result of uncontrolled urbanization (Njoh 2010), 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).

The important contribution of climatic variables such as temperature and associated changes in salinity, in the evolution and spread of cholera epidemics in Douala, has also been noted (Guévart et al., 2006; Tatah et al. 2012). The seasonality of cholera outbreaks proves that climatic factors play a big role in the endemicity of cholera in Douala (Guévart et al. 2006). The majority of previous attempts to establish the causes of cholera epidemics in Douala therefore 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 bacteria are 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 perception 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 a dangerously inadequate measure 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 as early as 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 however stand prominent amongst 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). Though these salient points have been stated earlier, they have however not been investigated intensively. This study exploits this gap and adds on another dimension not currently considered by researchers in the field; that is: gender–based cholera vulnerability. This is therefore an enquiry into the sociological characteristics of sections of communities of Douala which may provide vital insights into the nature of vulnerability of the populations to cholera, so as to tailor limited response resources efficiently and effectively.

2 MATERIALS AND METHODS

2.1 The Study area

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

illustration not visible in this excerpt

Figure 2: Map of Douala showing dense agglomerations within the Cameroon estuary. Yellow points represent main localities of data collection (Modified from Google Earth, [ 2012 ]

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 a nucleated 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.

[...]

^[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