Etiology, symptoms and treatment of cholera
Cholera is an intestinal disease caused by the bacterium Vibrio cholerae
which spreads mainly through faecal contamination of water and food by infected individuals [1
]. Eating raw or undercooked seafood can also cause the infection since V. cholerae
was found on phyto- and zooplankton in marine, estuarine and riverine environments independent of infected human beings [2
]. Two out of ca. 240 serogroups of V. cholerae
– O1 and O139 – are pathogenic. The O1 serogroup can further be subdivided into two biotypes – classical and El Tor.
After an incubation period of 18 hours to five days, infected individuals will develop acute watery diarrhoea. Large volumes of rice-water-like stool and concurrent loss of electrolytes can lead to severe dehydration and eventually death if patients are not rapidly treated. Most of the infected individuals, however, are asymptomatic or suffer only from mild diarrhoea. An inoculum of 108
bacteria is needed in healthy individuals to cause severe acute watery diarrhoea while a 1,000-fold lower dose is sufficient to cause the disease when gastric acid production is reduced. Other clinical features besides profuse diarrhoea (more than three loose stools per day) to establish a cholera diagnosis include abdominal and muscle cramps and frequent vomiting [4
]. Without treatment the case-fatality rate (CFR) can reach 50% [1
Treatment of cases depends on the severity and includes i) giving oral rehydration solutions (ORS) after each stool if no dehydration is apparent, ii) giving ORS in larger amounts if moderate dehydration is apparent, and iii) using intravenous drips of Ringer Lactate or saline for severely dehydrated patients [4
]. Antibiotics can be administered to shorten the episode in severe cases.
Prevention of cholera
Cholera usually occurs in epidemics and can cause major disruptions in affected health systems as rigorous measures have to be taken and patients treated in camps under quarantine-like conditions. Outbreaks of cholera can easily be prevented by providing safe water, sanitation and promoting good personal hygiene behaviour and safe food handling. Regions where such control measures have not been realised, or where maintenance and monitoring of existing schemes is not guaranteed, are at greatest risk of epidemics and consequently could become endemic with cholera.
The World Health Organization (WHO) has recently started to consider the use of vaccines as an additional public health tool to control cholera in low-income countries since the implementation of the above-mentioned prevention and control measures has not had the desired impact on cholera incidence [5
]. Currently only one safe and efficacious vaccine is available on the market – Dukoral®
– an oral cholera vaccine (OCV) consisting of killed whole-cell V. cholerae
O1 with purified recombinant B-subunit of cholera toxoid. It has to be administered in two doses about one week apart. It confers, as shown in field trials in Bangladesh, Peru and Mozambique, 60–85% protection for six months in young children and about 60% in older children and adults after two years [6
]. Longini Jr. et al. [9
] used data collected in 1985–1989 from a randomised controlled OCV trial in Bangladesh to calculate reductions of cholera cases. Their model indicated that a 50% coverage with OCV would lead to a 93% reduction in the entire population while a lower coverage of 30% would still reduce the cholera incidence by 76%.
Global and local burden of cholera
Cholera is mainly endemic in low-income countries in Africa, Asia, Central and South America. A total of 177,963 cases and 4,031 deaths, corresponding to a CFR of 2.3%, have been reported to WHO in 2007 with Africa having the largest share of worldwide reported cholera cases (94%) and deaths (99%) [10
]. This share of officially reported cases from Africa has increased considerably from 20% in the 1970s to 94% in the period 2000–2005 while the Asian share has simultaneously dropped from 80% to 5.2% over the same three decades [11
]. There is a similar picture with regard to reported deaths: Africa's share has increased from 22% to 97%, and Asia's has showed a steep decline from 77% to 2.4%. It has to be noted, however, that these official figures do not reflect the true burden of cholera since serious under-reporting due to technical (surveillance system limitations, problems with case definition and lack of standard vocabulary) and political (fear of travel or trade sanctions) reasons are suspected [10
]. Zuckerman et al. [12
] identified mainly under-reporting from the Indian subcontinent and Southeast Asia in a review carried out in 2004.
In Zanzibar, where this study will be conducted, a cholera outbreak with 411 cases and 51 deaths was reported for the first time in 1978 from a fishermen village [13
]. Thirteen outbreaks followed since then with almost annual episodes since the year 2000, with case-fatality rates ranging from 0% to 17% and showing a downward trend over the last two decades (Reyburn et al., unpublished data). During the last outbreaks in 2006/2007, 3,234 cases and 62 deaths were reported (CFR: 1.9%). A seasonal pattern can be observed that follows the rainy seasons (usually from March to June and from October to November) during which widespread flooding occurs frequently. Such deteriorating environmental conditions subsequently expose the majority of inhabitants on both islands to an increased risk of water-borne diseases due to the scarcity of safe drinking water supplies and a generally poor or lacking sanitation infrastructure in periurban and rural areas.
Despite all efforts in the past and the inexpensive and relatively easy use of ORS as major treatment [14
], cholera still poses a serious public health problem in low-income countries. Thus, a concerted action is needed to control cholera and to mitigate its health-related and economic consequences not only by maintaining and improving existing measures like water supply, sanitation and hygiene behaviour but also by assessing new prevention options like OCV mass vaccinations of vulnerable populations [5
Importance of sociocultural and behavioural research on vaccine introduction
Public health interventions to reduce disease burden must take into account the local realities to achieve a sustainable benefit for the affected populations. Solely relying on prevention or treatment measures that proved to be suitable in a given context does not necessarily make it appropriate for other situations.
Vaccination programmes have suffered a reduced coverage (e.g. rumours about tetanus toxoid causing infertility in Tanzania [16
]) or were even brought to a halt because of an ignorance of local realities (e.g. Northern Nigerian resistance to polio vaccination [17
]). Other interventions, especially when implemented in a top-down approach, experienced the same difficulties [19
To ensure the success of vaccination campaigns, a vaccine should not only be efficacious, relatively trouble-free for patients in its administration and preferably also cost-effective, but it is equally important that implementers consider community-held ideas, fears and individual help-seeking behaviour regarding the infectious disease and the vaccine of interest [22
Infrastructure, logistics, politics, and social and cultural features were identified as significant factors which determine vaccine acceptance and thus the success or failure of immunisation programmes in low-income countries [24
]. The importance of the social and cultural context on vaccine acceptance was assessed in various recent studies for typhoid fever and shigellosis (e.g. in Asian countries [27
]). It was reasserted that the importance of the social and cultural context on vaccine introduction has to be studied carefully in order to improve vaccination coverage [32
Research to improve the health of people needs to include gender issues since they play a crucial role in health and health planning [33
]. Gender differences are context-specific and thus require that sociocultural and behavioural research be done to complement clinical or epidemiological research. A recent review on the control of tropical diseases concluded that more detailed data about illness experience, meaning and help-seeking behaviour is needed on the gender level to inform the planning and execution of health interventions [34
Socioeconomic features, and cultural beliefs and practices, may vary across and within different sites or populations. And since differences in income, education, neighbourhood, infrastructure, etc. can affect people's health and behaviour regarding risk and relief, it is prudent to include site-specific analyses when doing research on the acceptance of community vaccine interventions.
Protocol review and ethical clearance
This paper summarises the protocol that had been reviewed by two independent scientists with expertise in the field of cholera and social science research before it was submitted to and accepted by the WHO Research Ethics Review Committee and the Ethics Committee of Zanzibar.
All participants will be informed about the study and individual written consent obtained before conducting discussions or interviews. All data will be handled with strict confidentiality and made anonymous before analysis.
Rationale for research: socioeconomic and behavioural (SEB) study
In late 2006, WHO received a grant from the Bill and Melinda Gates Foundation to work on the pre-emptive use of OCV in vulnerable populations at risk. The main focus of this grant is to examine how OCV can sustainably be used in countries with endemic cholera in addition to usually recommended control measures such as provision of safe water, adequate sanitation and health education. An important feature of the project is to collect evidence to assess the usefulness and financial stability of establishing an OCV stockpile.
To achieve these goals, WHO launched a joint venture with the Ministry of Health and Social Welfare of Zanzibar (MoHSW) to vaccinate 50,000 community residents older than two years living in communities at high risk of cholera with Dukoral®. The two islands of Zanzibar (Figure ) were chosen as study area since they have been regularly affected by cholera over the past three decades and since the local government wishes to enhance its strategy to control the disease and to examine the possibility of introducing OCV as a public health measure.
Map of Zanzibar with the two main islands. Courtesy of the University of Texas Libraries. The University of Texas at Austin.
Complementary to the vaccination campaign, since no sociocultural and behavioural studies related to cholera and OCV introduction have been conducted yet in African settings, the SEB study was conceived as a pilot project to address the research questions stated below. Besides the focus on cholera, it was also decided to include, to a lesser extent, shigellosis (bloody dysentery caused by Shigella spp.) in this research to investigate similarities and differences between the community perceptions of these two serious and potentially fatal diarrhoeal diseases.
Aims and research questions
The main aim of the SEB study, its stakeholders and research questions are as follows:
To generate evidence on the role socioeconomic and sociocultural factors can play to inform government policies regarding the introduction of OCV as part of a sustainable and financially viable cholera control strategy.
To inform the Government of Zanzibar, in particular the Ministry of Health and Social Welfare, regarding the national policy on cholera control and the use of OCV on the archipelago.
Research will be done on the following four stakeholder levels in Zanzibar:
- Level I: policy makers on national and regional level
- Level II: allopathic and traditional health care providers working in the target areas and district hospitals
- Level III: formal and informal local government and community leaders and teachers from the target areas
- Level IV: adult community residents (household level)
In populations where cholera is endemic:
- What are the perceptions of cholera in the context of diarrhoeal diseases, in particular shigellosis?
- What are the essential features of cholera and shigellosis?
- What is the acceptance of OCV?
For each question, the following comparisons will be made between:
- Site: periurban (Unguja) vs. rural (Pemba)
- Vaccination (intervention) status
- Stakeholders: all four levels