Winter 2015

UF study suggests cholera has become endemic in Haiti

By Thomas A. Weppelmann, Ph.D., M.P.H., C.P.H.

New research from the University of Florida College of Public Health and Health Professions suggests that after five years of cholera transmission in the impoverished island nation of Haiti, the outbreak may have become endemic. The findings appeared October 21 in the journal PLOS Neglected Tropical Diseases.

The study was led by Thomas A. Weppelmann, Ph.D., M.P.H., C.P.H., an adjunct faculty member and research scientist in the department of environmental and global health and a 2015 graduate of the department’s Ph.D. program, and Alexander Kirpich, Ph.D., a postdoctoral fellow in the department of molecular genetics and microbiology in the UF College of Medicine and a 2015 graduate of the Ph.D. program in the UF department of biostatistics.

The dynamic cholera transmission model used in the study.

The dynamic cholera transmission model used in the study.

Many mathematical models have been made from the cholera outbreak in Haiti, but our model is unique because it incorporated empirical data on the isolation of Vibrio cholerae O1 from surface waters in the Ouest Department of Haiti. We noticed that while 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 our 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 our dynamic model, we 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 our group at the Emerging Pathogens Institute, led by Afsar Ali, Ph.D., a research associate professor in the department of environmental and global health, and J. Glenn Morris, Jr., M.D., M.P.H.&T.M., the director of the Emerging Pathogens Institute. 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.

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