Epidemiological Significance of Cholera - Term Paper Example

EPIDEMIOLOGICAL SIGNIFICANCE OF CHOLERA ID Number Module and Number EPIDEMIOLOGICAL SIGNIFICANCE OF CHOLERA A) Using the Triangle of Epidemiology Explain the Outbreak, Transmission, and Control of Cholera Cholera emerged in ancient India, and began spreading to other countries in 1817 (Peters, 2007). Over the last two centuries, eight major pandemics occurred widely (Bailey et al., 2005). Today “the disease is endemic in southern Asia and parts of Africa and Latin America” (Faruque et al., 1998, p.1301), where seasonal outbreaks occur. The traditional model of causation of infectious diseases is the triangle of epidemiology (Bailey et al., 2005). Its three components for cholera include the bacterial specie Vibrium cholerae as the agent which colonises the small intestine and causes the severe watery diarrhea, a characteristic symptom of cholera produced by the enterotoxin: chloratoxin (CT) (Faruque et al., 1998). Poverty and man are the host; while unsanitary conditions, contaminated food and polluted water are the environmental factors facilitating interaction between the host and the agent (Bailey et al., 2005). Cholera is transmitted through the faecal-oral route. The bacteria’s 01 or 0139 antigen indicates a marker of epidemic potential for the disease. Outbreak of Cholera In the epidemiology of cholera, a characteristic feature is its emergence in a regular seasonal pattern in regions where the disease is endemic. It appears in explosive outbreaks frequently starting in numerous distinct foci concurrently, revealing the possibility of environmental factors forming the trigger for the epidemic process (Faruque et al., 1998). Currently, cholera is once again a public health priority requiring an integrated and comprehensive approach to controlling the disease. This is because of the changed dynamics of cholera occurrence, besides “the emergence of new strains of V. Cholerae that cause more severe clinical manifestations, increased antimicrobial resistance, and climate change” (World Health Organization, 2012, p.294). The cholera outbreak in west Africa which spread to central Africa in 2005 affected over eight countries, causing tens of thousands of cases, and high mortality. The high incidence from the outbreak is attributed to the host factor of poverty, and environmental factors related to heavy rains causing flooding and water contamination. Because of poor surveillance, the actual extent of the problem is unknown (Editorial, 2005). Transmission of Cholera The transmission of an epidemic of cholera following its outbreak occurs in three time periods: “the primary, saturation, and the waning phases” (Kwofie, 1976, p.128). In the study conducted on the complex cholera epidemic pattern in Western Africa from 1970 to 1972, two principal paths of diffusion were identified from the general trend; these included the regular pattern of the coastal path and the more complicated pattern of the Sahelian path. In all cases “the person-to-person and the person-to-environment-to-person modes of spread were operative” (Kwofie, 1976, p.133). The rate at which the epidemic spread as well as the attack rates were both higher along complex movement networks, and in areas with little access to medical facilities. The outbreak and transmission of cholera in Haiti in 2011 has been examined with the help of a mathematical model to understand its epidemic processes, and to help formulate control strategies. The sequence and timing of regional cholera epidemics in Haiti were predicted, and the potential effects of disease-control strategies were examined by Tuite et al. (2011). The compartmental mathematical model simulated person-to-person and waterborne transmission of cholera. Thus, despite inadequate surveillance data, “the model simulating between-region disease transmission according to population and distance closely reproduces reported disease patterns” (Tuite et al., 2011, p.593). This model has been acknowledged as a suitable tool for planners, policymakers, and medical personnel to immediately manage a cholera epidemic. Andrews and Basu’s (2011) used a mathematical model of the epidemic in Haiti to provide projections of future morbidity and mortality, and to produce comparative estimates of the effects of proposed interventions. They argue that the decline in cholera prevalence in early 2011 was based on the natural course of the epidemic, and did not indicate the outcome of successful intervention. The work of Cortez and Weitz (2013, E43) reveals how the transmission pathway from population level time series can be identified from the differences in the transmission pathway which can result in quantitatively different epidemiological dynamics. A mathematical model presented by Sanches et al. (2011, p.2916) consists of “seasonality, loss of host immunity, and control mechanisms acting to reduce cholera transmission”. A collection of data on cholera reveals that outbreaks of the disease in endemic areas are subject to a resonant, oscillatory behaviour. Further, a short period of host immunity may be related to secondary peaks of incidence found in some regions, in a bimodal pattern. To prevent thousands of deaths from the transmission of cholera, besides mass vaccination which may be impracticable, improvements in sanitation systems as well as food/ personal hygiene, besides increased access to antibiotics were recommended as the most effective approaches (Sanches et al., 2011). Control of Cholera “Cholera dynamics in endemic regions display regular seasonal cycles and pronounced interannual variability” (Pascual et al., 2002, p.237). The authors examine the quantitative evidence relating to the impact of climate on cholera dynamics. They argue that mathematical models for the disease significantly help to understand climatic influences in relation to population dynamics of the disease. The role of the environment in increasing the disease risk emphasizes the requirement for changing the socioeconomic conditions which contribute to the prevalence of cholera. Einarsdottir et al. (2001) undertook a study in a rural community in West Africa to explore local ideas about cholera, the extent to which official health educational messages for cholera prevention had diffused to the local people, and to evaluate whether such messages resulted in the population’s implementation of recommendations. The authors found that to control cholera through increased compliance with the preventive measures suggested, the local conceptions of diseases should be taken into account, and prevention should be restricted to a few key practices, practical and effective. The radio’s influence could be widened by urging those who hear the messages to spread the recommendations, specifically to women who are responsible for food, water and sanitation in the household. The evidence indicates the effectiveness of the radio together with word-of-mouth communication for the dissemination of health messages. Further, the prevention and control of cholera could be promoted more effectively by explaining the routes of transmission, based on local competing ideas about transmission of diseases (Einarsdottir et al, 2001). The solar disinfection of water at the point of consumption is recommended by Conroy et al. (2001, p.293) as “an important first line response to cholera outbreaks” and to reduce the risk of water-borne infection among children younger than six years of age. This intervention requires readily available minimal resources. Similarly, the surveillance and microbial screening of travellers from infected areas would need to be mandatory, but may not be feasible, states Behrens (1991). Further control mechanisms for cholera epidemics require changing the socioeconomic situation of endemic populations to promote better sanitation and living conditions, ensuring the boiling or chlorination of water, the protection of food particularly fish and vegetables from contamination, and the establishment and enforcement of environmental sanitation. Other important measures include the isolation of cases, provision of medical treatment and the rendering of affected individuals non-infectious. Similarly, the monitoring and treatment of contacts is essential. Significantly, the use of oral rehydration salts have been found to be effective in controlling 90% of cases of cholera (Behrens, 1991). B) Explain the Meaning of Prevalence Rate and Briefly Highlight Four Factors that Can Lead to an Increase in Prevalence Rate “The prevalence rate is the proportion of persons in a population that have a particular disease at a specific point in time, or over a specified period of time” (Osborn, 2006, p.18). Two types of prevalence rates include ‘point prevalence’ and ‘period prevalence’. Point prevalence indicates the existence of a disease condition at a particular point in time, while period prevalence refers to the “existence of a condition during an interval of time” (Lundy & Janes, 2009, p.109). The formula for calculating the prevalence rate of a disease is as follows (Osborn, 2006, p.18): All new and pre-existing cases during a time period x 10n Prevalence Rate = ______________________________________________________________ Total population during the same time period Prevalence measures the extent of illness or morbidity in a community resulting from the specific disease under investigation. Unlike prevalence rate “which includes all individuals ill from a specified cause, regardless of when the illness began” (Osborn, 2006, p.18), incidence rate includes only new cases at a given time period. Knowledge about the prevalence of a condition in a particular population can help in projecting the extent of medical treatment required, and in planning community and public services to meet the special needs of those afflicted with the disease (Timmreck, 2002). The four main factors that can lead to an increase in the prevalence rate include: 1. With the development of a new disease in a population, the incidence of the condition rises; this results in a consequent increase in its prevalence rate (Timmreck, 2002). Similarly, the severity of the disease also impacts its prevalence rate. In the case of cholera, higher levels of poverty, a lack of adequate environmental sanitation, non-availability of clean drinking water and contaminated food particularly fish and vegetables lead to greater prevalence rate (Behrens, 1991). 2. The duration of the disease impacts its prevalence rate, with increased prevalence rate occurring for a longer time, with greater duration of the disease (Timmreck, 2002). Thus, lack of suitable diagnostic and medical facilities for early detection and intervention cause higher prevalence rate. 3. The adequacy of interventions and treatment are important for reducing the prevalence of a disease. For example, the administration of oral rehydration salts as a first line of treatment are found to effectively manage 90% of cholera outbreak cases. On the other hand, prolongation of the life of cases without cure increases the duration and prevalence rate of the disease (Behrens, 1991). 4. The immigration of ill cases into the community, or new arrivals in the form of susceptible individuals with a potential for aquiring the condition, in the region (Timmreck, 2002). This occurs when surveillance and microbial screening of travellers from infected areas are not conducted. Similarly, the prevalence increases in the absence of mandatory vaccination of travellers to control the spread of the disease. Further, the prevalence rate increases if the cardinal principles of isolation, treatment, and rendering cases non-infectious, as well as monitoring and treating contacts, are not undertaken (Behrens, 1991). Besides the immigration of infected individuals, the outmigration of healthy individuals, from the community also leads to a rise in prevalence rates of the disease (Timmreck, 2002). Bibliography Andrews, J.R. and Basu, S. (2011). Transmission dynamics and control of cholera in Haiti: An epidemic model. The Lancet, 377 (9773), pp.1248-1255. Bailey, L., Vardulaki, K., Langham, J. and Chandramohan, D. (2005). Introduction to epidemiology. Maidenhead, England: Open University Press. Behrens, R.H. (1991). Cholera. British Medical Journal, 302, pp.1033-1034. Conroy, R.M., Meegan, M.E., Joyce, T., McGuigan, K. and Barnes, J. (2001). Solar disinfection of drinking water protects against cholera in children under 6 years of age. Archives of Disease in Childhood, 85, pp.293-295. Cortez, M.H. and Weitz, J.S. (2013). Distinguishing between indirect and direct modes of transmission using epidemiological time series. The American Naturalist, 181 (2), pp.E43-E54. Editorial. (2005). 150 years of cholera epidemiology. The Lancet, 366 (9490), p.957. Einarsdottir, J., Passa, A. and Gunnlaugsson, G. (2001). Health education and cholera in rural Guinea-Bissau. International Journal of Infectious Diseases, 5, pp.5133- 5138. Faruque, S.M., Albert, M.J. and Mekalanos, J.J. (1998). Epidemiology, genetics, and ecology of toxigenic Vibrio chorae. Microbiology and Molecular Biology Reviews, 62 (4), pp.1301-1314. Kwofie, K.M. (1976). A spatio-temporal analysis of cholera diffusion in Western Africa. Reviewed Works. Human Health Problems: Spatial Perspectives. Economic Geography, 52 (2), pp.127-135/ Lundy, K.S. and Janes, S. (2009). Community health nursing: Caring for the public’s health. Edition 2. London: Jones and Bartlett Learning. Osborn, C.E. (2006). Statistical applications for health information management. Edition 2. London: Jones and Bartlett Learning. Pascual, M., Bouma, M.J. and Dobson, A.P. (2002). Cholera and climate: Revisiting the quantitative evidence. Microbes and Infection, 4 (2), pp.237-245. Peters, S.T. (2004). Cholera: Curse of the nineteenth century. The United Kingdom: Marshall Cavendish. Sanches, R.P., Ferreira, C.P. and Kraenkel, R.A. (2011). The role of immunity and seasonality in cholera epidemics. Bulletin of Mathematical Biology, 73 (12), pp.2916- 2931. Timmreck, T.C. (2002). An introduction to epidemiology. Edition 3. London: Jones and Bartlett Learning. Tuite, A.R., Tien, J., Eisenberg, M., Earn, D.J., Ma, J. and Fisman, D.N. (2011). Cholera epidemic in Haiti, 2010: Using a transmission model to explain spatial spread of disease and identify optimal control interventions. Annals of Internal Medicine, 145 (9), pp.593-601. World Health Organization. (2012, August 3). Weekly epidemiological record. World Health Organization, 87 (31-32), pp.289-304. Read More