New research from the University of Florida College of Public Health and Health Professions has suggested that after five years of cholera transmission in the impoverished island nation of Haiti, the outbreak may have become endemic. The study, led by Dr. Thomas A. Weppelmann from the department of environmental and global health and Dr. Alexander Kirpich from the department of biostatistics and, was published on October 21 in the journal PLOS Neglected Tropical Diseases.
Many mathematical models have been made from the cholera outbreak in Haiti, however their model was unique because it incorporated empirical data on the isolation of Vibrio cholerae O1 from surface waters in the Ouest Department of Haiti. They noticed that though the weekly reported cases seemed to be declining in the third and fourth years of the outbreak, the frequency of isolation of toxigenic V. cholerae in the environment was actually increasing. Under the current dogma of cholera transmission models, V. cholerae shed by humans into the environment only exists in a transient state governed by a constant rate of decay. The assumption is that although V. cholerae is an aquatic pathogen, it lacks the ability to replicate and survive for prolonged periods in surface waters. Given their understanding of V. cholerae biology, this is likely an oversimplification which precluded the possibility for an increase in environmental concentrations during a period where cholera incidence was infrequent or declining, as was observed in Haiti.
For their dynamic model, they simulated the environmental compartment separately based on the biology of causative bacterium and the shedding of V. cholerae O1 by humans into the environment. The effects of precipitation and water temperature on the concentration and survival of V. cholerae in aquatic reservoirs was also included to reflect observations made by their group at the Emerging Pathogens Institute led by Dr. Afsar Ali and Dr. J. Glenn Morris, Jr. Based on the model-fitted trend and the observed incidence, there is evidence that after an initial period of intense transmission, the cholera epidemic in Haiti stabilized during the third year of the outbreak and became endemic. The model estimates indicate that the proportion of the population susceptible to infection is increasing and that the presence of toxigenic V. cholerae in the environment remains a potential source of new infections. Given the lack of adequate improvements to drinking water and sanitation infrastructure, these conditions could facilitate ongoing, seasonal cholera epidemics in Haiti. Without further intervention from the international community, the goal of cholera elimination from the island of Hispaniola by 2022 will be more challenging, with the potential for cholera to become endemic in Haiti.
Article link: http://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0004153