Search

Although diseases such as influenza, tuberculosis and SARS are transmitted through an environmentally mediated mechanism, most modeling work on these topics is based on the concepts of infectious contact and direct transmission. In this paper we use a paradigm model to show that environmental transmission appears like direct transmission in the case where the pathogen persists little time in the environment. Furthermore, we formulate conditions for the validity of this modeling approximation and we illustrate them numerically for the cases of cholera and influenza. According to our results based on recently published parameter estimates, the direct transmission approximation fails for both cholera and influenza. While environmental transmission is typically chosen over direct transmission in modeling cholera, this is not the case for influenza.

Many factors influencing disease transmission vary throughout and across populations. For diseases spread through multiple transmission pathways, sources of variation may affect each transmission pathway differently. In this paper we consider a disease that can be spread via direct and indirect transmission, such as the waterborne disease cholera. Specifically, we consider a system of multiple patches with direct transmission occurring entirely within patch and indirect transmission via a single shared water source. We investigate the effect of heterogeneity in dual transmission pathways on the spread of the disease. We first present a 2-patch model for which we examine the effect of variation in each pathway separately and propose a measure of heterogeneity that incorporates both transmission mechanisms and is predictive of R(0). We also explore how heterogeneity affects the final outbreak size and the efficacy of intervention measures. We conclude by extending several results to a more general n-patch setting.

There has been little evidence of a decline in the global burden of cholera in recent years as the number of cholera cases reported to WHO continues to rise. Cholera remains a global threat to public health and a key indicator of lack of socioeconomic development. Overall socioeconomic development is the ultimate solution for control of cholera as evidenced in developed countries. However, most research has focused on cross-county comparisons so that the role of individual- or small area-level socioeconomic status (SES) in cholera dynamics has not been carefully studied. Reported cases of cholera in Matlab, Bangladesh have fluctuated greatly over time and epidemic outbreaks of cholera continue, most recently with the introduction of a new serotype into the region. The wealth of longitudinal data on the population of Matlab provides a unique opportunity to explore the impact of socioeconomic status and other demographic characteristics on the long-term temporal dynamics of cholera in the region. In this population-based study we examine which factors impact the initial number of cholera cases in a bari at the beginning of the 0139 epidemic and the factors impacting the number of cases over time. Cholera data were derived from the ICDDR,B health records and linked to socioeconomic and geographic data collected as part of the Matlab Health and Demographic Surveillance System. Longitudinal zero-inflated Poisson (ZIP) multilevel regression models are used to examine the impact of environmental and socio-demographic factors on cholera counts across baris. Results indicate that baris with a high socioeconomic status had lower initial rates of cholera at the beginning of the 0139 epidemic (γ(01) = -0.147, p = 0.041) and a higher probability of reporting no cholera cases (α(01) = 0.156, p = 0.061). Populations in baris characterized by low SES are more likely to experience higher cholera morbidity at the beginning of an epidemic than populations in high SES baris.

Cholera reappeared in Haiti in October, 2010 after decades of absence. Cases were first detected in Artibonite region and in the ensuing months the disease spread to every department in the country. The rate of increase in the number of cases at the start of epidemics provides valuable information about the basic reproductive number (R(0)). Quantitative analysis of such data gives useful information for planning and evaluating disease control interventions, including vaccination. Using a mathematical model, we fitted data on the cumulative number of reported hospitalized cholera cases in Haiti. R(0) varied by department, ranging from 1.06 to 2.63. At a national level, 46% vaccination coverage would result in an (R(0)) <1, which would suppress transmission. In the current debate on the use of cholera vaccines in endemic and non-endemic regions, our results suggest that moderate cholera vaccine coverage would be an important element of disease control in Haiti.

Introduction: Estimate the efficacy of oral anticholeric vaccine Dukoral in subjects travelling to high-risk areas for traveler's diarrhoea and cholera., Methods: The study involved subjects of both genders who planned to travel to high-risk areas for traveler's diarrhoea and cholera. Immunization with oral anticholeric vaccine Dukoral was offered to each one of them. Upon returning, all the participants in the study were asked to complete a self-administered questionnaire consisting of 40 close-ended questions mainly concerning: personal and health data, characteristics (length, destination, reason) of the travel, onset of gastrointestinal symptoms, data relating to the assumption of anticholeric vaccine and possible adverse reactions., Results: 296 questionnaires have been collected. Mean age was 38.2 years (55.4% males and 44.6% females). Mean travel length was 22.2 days. Reasons for the travel: 66.8% tourism and 33.2% work-cooperation. Most frequent destination was Africa (48.1%), followed by Asia (32.1%) and central South-America (17.8%). 199 subjects (67.2%) properly executed vaccination with Dukoral. The diarrhoea affected 14.1% of vaccinated subjects and 20.6% of non vaccinated ones. The following cohorts showed statistically significant differences in incidence of diarrhoea: <35 years old age (13.7% vs. 27.1%), travel for work-cooperation (14.1% vs. 35%) and travel length >28 days (12.1% vs. 40%). No serious adverse events were reported following vaccination., Discussion: Oral Anticholeric vaccine proved to be effective and safe in preventing fecal-oral diseases in travelers exposed to high risk conditions.

Objective: Occupational infections particularly hospital-acquired infections (HAIs) are a serious problem in the healthcare industry worldwide. This study purported to investigate their prevalence and risk factors among healthcare workers from Limpopo province of South Africa., Methods: Cases about occupational infectious diseases of healthcare workers from Limpopo province that were submitted to the Compensation Commissioner from January 2006 to December 2009 were reviewed., Results: The total number of cases of infectious diseases reported during the study period was 56; of these, 83.9% (47) of cases were for tuberculosis, 10.7% (6) for cholera, and 5.4% (3) for chickenpox. Nurses were the most affected. Risk factors associated with the acquisition of infection diseases were as follows. The majority of those infected were female (67.9%), aged over 40 years (57.1%), and who had worked for over 10 years (59.2%). With regard to length of time it took for one to be infected, overall it took 13.6±9.7 years from the year of employment to being infected. This duration was just 5.7±4.2 years in HCWs younger than 40 years versus 18.4±9.0 years in those 40 years and over (p=0.001); and 11.4±10.3 years in nurses versus 17.1±7.8 years in non-professional staff members (p=0.046). Mopani district, situated in a rural setting was the most affected as 24 of the 47 cases of tuberculosis occurred there., Conclusion: In conclusion, the most common occupational infection or hospital acquired infection among healthcare workers in Limpopo province of South Africa was tuberculosis. It infected mainly nurses from the rural health district of Mopani. Younger age and being a nurse were significant risk factors associated with being infected early.

Organisms, including Vibrio cholerae, can be transferred between harbors in the ballast water of ships. Zones in the Caribbean region where distance from shore and water depth meet International Maritime Organization guidelines for ballast water exchange are extremely limited. Use of ballast water treatment systems could mitigate the risk for organism transfer.

The case of John Snow has long been important to epidemiologists and public health officials. However, despite the fact that there have been many discussions about the various aspects of Snow's case, there has been virtually no discussion about what guided Snow's reasoning in his coming to believe his various conclusions about cholera. Here, I want to take up this question in some detail and show that there are a number of specific principles of reasoning that played a crucial role for Snow. Moreover, these principles were epistemologically important to Snow, a fact about which Snow is explicit in many places. An analysis of Snow's case suggests that, because of the epistemic role such principles of reasoning can play, health care practitioners ought to understand their practices to be theoretically informed in these ways, and not just data driven., (© 2012 Blackwell Publishing Ltd.)

A mathematical model for cholera is formulated that incorporates hyperinfectivity and temporary immunity using distributed delays. The basic reproduction number R(0) is defined and proved to give a sharp threshold that determines whether or not the disease dies out. The case of constant temporary immunity is further considered with two different infectivity kernels. Numerical simulations are carried out to show that when R(0) > 1, the unique endemic equilibrium can lose its stability and oscillations occur. Using cholera data from the literature, the quantitative effects of hyperinfectivity and temporary immunity on oscillations are investigated numerically.

Hainanese chicken rice (cooked rice mixed with chicken fat and served with sliced chicken and cucumber) is a well-known Chinese dish in Southeast Asian countries. We report two consecutive outbreaks of cholera associated with consumption of chicken rice among attendants of two meetings in northwestern Thailand in April 2010. Active case finding was carried out among persons who attended the meetings and in the community. Environmental investigation was conducted at the implicated food shop and in the affected areas. The first outbreak involved 17 cholera cases (35.4%) among 48 attendants and 16 cases in the community. The onset of symptoms was between April 19 and 23, 2010. People who ate the chicken rice had a higher attack rate of infection than those who did not. All 12 food handlers at the implicated food shop were screened for cholera infection by rectal swab culture; 3 were culture-positive. Although the food shop was closed temporarily following the outbreak, some chicken rice was produced and served at the second meeting and caused 11 more cases (23.4%) among 47 meeting attendants. All cholera isolates obtained from patients and food handlers were V. cholerae O1, biotype El Tor, serotype Ogawa, and had similar antibiograms and genetic patterns by pulsed-field gel electrophoresis. The chicken rice which was possibly contaminated by an infected food handler served as the vehicle of transmission. A repeat cholera outbreak caused by the same vehicle can occur when control measures are not adequately followed.

Several mathematical models of epidemic cholera have recently been proposed in response to outbreaks in Zimbabwe and Haiti. These models aim to estimate the dynamics of cholera transmission and the impact of possible interventions, with a goal of providing guidance to policy makers in deciding among alternative courses of action, including vaccination, provision of clean water, and antibiotics. Here, we discuss concerns about model misspecification, parameter uncertainty, and spatial heterogeneity intrinsic to models for cholera. We argue for caution in interpreting quantitative predictions, particularly predictions of the effectiveness of interventions. We specify sensitivity analyses that would be necessary to improve confidence in model-based quantitative prediction, and suggest types of monitoring in future epidemic settings that would improve analysis and prediction.

Vibrio cholerae O1 causes cholera, a dehydrating diarrheal disease. We have previously shown that V. cholerae-specific memory B cell responses develop after cholera infection, and we hypothesize that these mediate long-term protective immunity against cholera. We prospectively followed household contacts of cholera patients to determine whether the presence of circulating V. cholerae O1 antigen-specific memory B cells on enrollment was associated with protection against V. cholerae infection over a 30-day period. Two hundred thirty-six household contacts of 122 index patients with cholera were enrolled. The presence of lipopolysaccharide (LPS)-specific IgG memory B cells in peripheral blood on study entry was associated with a 68% decrease in the risk of infection in household contacts (P = 0.032). No protection was associated with cholera toxin B subunit (CtxB)-specific memory B cells or IgA memory B cells specific to LPS. These results suggest that LPS-specific IgG memory B cells may be important in protection against infection with V. cholerae O1.

A non-linear SIRS mathematical model to explore the dynamics of water borne diseases like cholera is proposed and analyzed by incorporating delay in using disinfectants to control the disease. It is assumed that the only way for the spread of infection is ingestion of contaminated water by susceptibles. As the pathogens discharged by infectives reach to the aquatic environment, it is assumed that the growth rate of pathogens is proportional to the number of infectives. Further, it is assumed that disinfectants are introduced to kill pathogens with a rate proportional to the density of pathogens in the aquatic environment. The model is analyzed by using stability theory of delay differential equations. It is found that the model exhibits two equilibria, the disease free equilibrium and the endemic equilibrium. The analysis shows that under certain conditions, the cholera disease may be controlled by using disinfectants but a longer delay in their use may destabilize the system. Numerical simulation is also carried out to confirm the analytical results.

Mathematical models can provide key insights into the course of an ongoing epidemic, potentially aiding real-time emergency management in allocating health care resources and by anticipating the impact of alternative interventions. We study the ex post reliability of predictions of the 2010-2011 Haiti cholera outbreak from four independent modeling studies that appeared almost simultaneously during the unfolding epidemic. We consider the impact of different approaches to the modeling of spatial spread of Vibrio cholerae and mechanisms of cholera transmission, accounting for the dynamics of susceptible and infected individuals within different local human communities. To explain resurgences of the epidemic, we go on to include waning immunity and a mechanism explicitly accounting for rainfall as a driver of enhanced disease transmission. The formal comparative analysis is carried out via the Akaike information criterion (AIC) to measure the added information provided by each process modeled, discounting for the added parameters. A generalized model for Haitian epidemic cholera and the related uncertainty is thus proposed and applied to the year-long dataset of reported cases now available. The model allows us to draw predictions on longer-term epidemic cholera in Haiti from multiseason Monte Carlo runs, carried out up to January 2014 by using suitable rainfall fields forecasts. Lessons learned and open issues are discussed and placed in perspective. We conclude that, despite differences in methods that can be tested through model-guided field validation, mathematical modeling of large-scale outbreaks emerges as an essential component of future cholera epidemic control.

The cholera burden has grown strikingly during the past 4 years, and has spread to countries previously spared by this disease. The current spread has proved especially violent, as illustrated by the recent deadly epidemics around the Lake Chad Basin, in East Africa, and in Haiti. This onset of severe cholera epidemics is part of the overall dynamic of the current seventh cholera pandemic, composed of successive epidemic waves. The current wave is attributable to new atypical El Tor strains, which spread from the Bay of Bengal to Papua in the east, Africa, and the Caribbean Sea in the west, and caused hundreds of thousands of cases and thousands of deaths during each of the last 4 years. The particular severity of the resulting epidemics is partially attributable to the specific characteristics of the atypical El Tor strain involved. Besides the abilty of El Tor to spread easily, this strain is associated with more severe clinical findings, because of elevated levels of toxin secretion resulting from a genetic content originating from classical strains. Conversely, recent studies of these deadly outbreaks raised hope by illustrating their relationship with human-borne dissemination rather than with the resurgence of environmental strains. As human-borne dissemination can be more easily targeted than ubiquitous environmental contamination, accurate and comprehensive epidemiological studies are essential to better understand the dynamics of the disease and to optimize future cholera responses., (© 2012 The Authors. Clinical Microbiology and Infection © 2012 European Society of Clinical Microbiology and Infectious Diseases.)

We investigate the role of human mobility as a driver for long-range spreading of cholera infections, which primarily propagate through hydrologically controlled ecological corridors. Our aim is to build a spatially explicit model of a disease epidemic, which is relevant to both social and scientific issues. We present a two-layer network model that accounts for the interplay between epidemiological dynamics, hydrological transport and long-distance dissemination of the pathogen Vibrio cholerae owing to host movement, described here by means of a gravity-model approach. We test our model against epidemiological data recorded during the extensive cholera outbreak occurred in the KwaZulu-Natal province of South Africa during 2000-2001. We show that long-range human movement is fundamental in quantifying otherwise unexplained inter-catchment transport of V. cholerae, thus playing a key role in the formation of regional patterns of cholera epidemics. We also show quantitatively how heterogeneously distributed drinking water supplies and sanitation conditions may affect large-scale cholera transmission, and analyse the effects of different sanitation policies.

Background: Vibrio cholerae excreted by cholera patients is "hyperinfectious" (HI), which can be modeled by passage through infant mice. Immunization of adult female mice with V. cholerae outer-membrane vesicles (OMVs) passively protects suckling mice from challenge. Although V. cholerae is unable to colonize protected pups, the bacteria survive passage and have the potential to be transmitted to susceptible individuals. Here, we investigated the impact of OMV immunization and the HI state on V. cholerae transmission., Methods: Neonatal mice suckled by OMV- or sham-immunized dams were challenged with HI V. cholerae. The infectivity of spatially and temporally separate V. cholerae populations obtained from infected naive or protected pups was tested. Recombination-based in vivo expression technology was used to assess virulence gene expression within these populations., Results: OMV immunization significantly reduced colonization of neonates challenged with HI V. cholerae. Vibrio cholerae that had colonized the naive host was HI, whereas V. cholerae excreted by neonates born to OMV-immunized dams, although viable, was hypoinfectious and failed to fully induce virulence gene expression., Conclusions: OMV immunization can significantly reduce the V. cholerae burden upon challenge with HI V. cholerae and can also block transmission from immune mice by reducing the infectivity of shed bacteria.

Background: Use of cholera vaccines in response to epidemics (reactive vaccination) may provide an effective supplement to traditional control measures. In Haiti, reactive vaccination was considered but, until recently, rejected in part due to limited global supply of vaccine. Using Bissau City, Guinea-Bissau as a case study, we explore neighborhood-level transmission dynamics to understand if, with limited vaccine and likely delays, reactive vaccination can significantly change the course of a cholera epidemic., Methods and Findings: We fit a spatially explicit meta-population model of cholera transmission within Bissau City to data from 7,551 suspected cholera cases from a 2008 epidemic. We estimated the effect reactive vaccination campaigns would have had on the epidemic under different levels of vaccine coverage and campaign start dates. We compared highly focused and diffuse strategies for distributing vaccine throughout the city. We found wide variation in the efficiency of cholera transmission both within and between areas of the city. "Hotspots", where transmission was most efficient, appear to drive the epidemic. In particular one area, Bandim, was a necessary driver of the 2008 epidemic in Bissau City. If vaccine supply were limited but could have been distributed within the first 80 days of the epidemic, targeting vaccination at Bandim would have averted the most cases both within this area and throughout the city. Regardless of the distribution strategy used, timely distribution of vaccine in response to an ongoing cholera epidemic can prevent cases and save lives., Conclusions: Reactive vaccination can be a useful tool for controlling cholera epidemics, especially in urban areas like Bissau City. Particular neighborhoods may be responsible for driving a city's cholera epidemic; timely and targeted reactive vaccination at such neighborhoods may be the most effective way to prevent cholera cases both within that neighborhood and throughout the city.

Cholera is an acute diarrhoeal infection caused by ingestion of food or water contaminated with the bacterium, Vibrio cholera. Choleragenic V. cholera O1 and O139 are the only causative agents of the disease. The two most distinguishing epidemiologic features of the disease are its tendency to appear in explosive outbreaks and its predisposition to causing pandemics that may progressively affect many countries and spread into continents. Despite efforts to control cholera, the disease continues to occur as a major public health problem in many developing countries. Numerous studies over more than a century have made advances in the understanding of the disease and ways of treating patients, but the mechanism of emergence of new epidemic strains, and the ecosystem supporting regular epidemics, remain challenging to epidemiologists. In Nigeria, since the first appearance of epidemic cholera in 1972, intermittent outbreaks have been occurring. The later part of 2010 was marked with severe outbreak which started from the northern part of Nigeria, spreading to the other parts and involving approximately 3,000 cases and 781 deaths. Sporadic cases have also been reported. Although epidemiologic surveillance constitutes an important component of the public health response, publicly available surveillance data from Nigeria have been relatively limited to date. Based on existing relevant scientific literature on features of cholera, this paper presents a synopsis of cholera epidemiology emphasising the situation in Nigeria.

In this paper, we conduct a careful global stability analysis for a generalized cholera epidemiological model originally proposed in [J. Wang and S. Liao, A generalized cholera model and epidemic/endemic analysis, J. Biol. Dyn. 6 (2012), pp. 568-589]. Cholera is a water- and food-borne infectious disease whose dynamics are complicated by the multiple interactions between the human host, the pathogen, and the environment. Using the geometric approach, we rigorously prove the endemic global stability for the cholera model in three-dimensional (when the pathogen component is a scalar) and four-dimensional (when the pathogen component is a vector) systems. This work unifies the study of global dynamics for several existing deterministic cholera models. The analytical predictions are verified by numerical simulation results.

Background: Vibrio cholerae O1 El Tor dominated the seventh cholera pandemic which occurred in the 1960s. For two decades, variants of V. cholerae O1 El Tor that produce classical cholera toxin have emerged and spread globally, replacing the prototypic El Tor biotype. This study aims to characterize V. cholerae O1 isolates from outbreaks in Thailand with special reference to genotypic variations over time., Methods/findings: A total of 343 isolates of V. cholerae O1 from cholera outbreaks from 2007 to 2010 were investigated, and 99.4% were found to carry the classical cholera toxin B subunit (ctxB) and El Tor rstR genes. Pulsed-field gel electrophoresis (PFGE) differentiated the isolates into 10 distinct pulsotypes, clustered into two major groups, A and B, with an overall similarity of 88%. Ribotyping, multiple-locus variable-number tandem-repeat analysis (MLVA), and PCR to detect Vibrio seventh pandemic island II (VSP-II) related genes of randomly selected isolates from each pulsotype corresponded to the results obtained by PFGE. Epidemiological investigations revealed that MLVA type 2 was strongly associated with a cholera outbreak in northeastern Thailand in 2007, while MLVA type 7 dominated the outbreaks of the southern Gulf areas in 2009 and MLVA type 4 dominated the outbreaks of the central Gulf areas during 2009-2010. Only MLVA type 16 isolates were found in a Thai-Myanmar border area in 2010, whereas those of MLVA types 26, 39, and 41 predominated this border area in 2008. Type 39 then disappeared 1-2 years later as MLVA type 41 became prevalent. Type 41 was also found to infect an outbreak area., Conclusions: MLVA provided a high-throughput genetic typing tool for understanding the in-depth epidemiology of cholera outbreaks. Our epidemiological surveys suggest that some clones of V. cholerae O1 with similar but distinctive genetic traits circulate in outbreak sites, while others disappear over time.

A general compartmental model for cholera is formulated that incorporates two pathways of transmission, namely direct and indirect via contaminated water. Non-linear incidence, multiple stages of infection and multiple states of the pathogen are included, thus the model includes and extends cholera models in the literature. The model is analyzed by determining a basic reproduction number R0 and proving, by using Lyapunov functions and a graph-theoretic result based on Kirchhoff's Matrix Tree Theorem, that it determines a sharp threshold. If R0≤1, then cholera dies out; whereas if R0>1, then the disease tends to a unique endemic equilibrium. When input and death are neglected, the model is used to determine a final size equation or inequality, and simulations illustrate how assumptions on cholera transmission affect the final size of an epidemic., (Copyright © 2011 Elsevier Inc. All rights reserved.)

With steam navigation, men, but also seeds of diseases, move faster. In 1865, the pilgrimage to Mecca induced a terrible cholera pandemic. This caused deep trauma in Europe and prompted the international community, recently born, to focus on the pilgrims who were regarded as the main "risk group" in the spread of epidemics. Through a series of international sanitary conferences, European powers, in agreement with the Ottoman Empire, imposed a heavy control over the pilgrims, much harsher than that applied to ordinary commercial navigation exchanges. These decisions led to the establishment of a huge quarantine device in the Red Sea and the Levant, including two lazaretto, one at the entrance and the other at the exit of the Red Sea, where the pilgrims were trapped and disinfected during their sacred journey. This contrasted with the concommitant disappearance of quarantines everywhere else. The pilgrims did not show hostility towards medical and prophylactic treatments but protested against the dehumanizing conditions of their realization. The combined pressures of nationalism and sovereignty claims from Saudi Arabia ended this system in 1957., (© 2011 médecine/sciences – Inserm / SRMS.)

This paper presents a mathematical model for cholera epidemics which comprises seasonality, loss of host immunity, and control mechanisms acting to reduce cholera transmission. A collection of data related to cholera disease allows us to show that outbreaks in endemic areas are subject to a resonant behavior, since the intrinsic oscillation period of the disease (∼1 year) is synchronized with the annual contact rate variation. Moreover, we argue that the short period of the host immunity may be associated to secondary peaks of incidence observed in some regions (a bimodal pattern). Finally, we explore some possible mechanisms of cholera control, and analyze their efficiency. We conclude that, besides mass vaccination--which may be impracticable--improvements in sanitation system and food/personal hygiene are the most effective ways to prevent an epidemic.

During the 2010 cholera outbreak in Haiti, water and seafood samples were collected to detect Vibrio cholerae. The outbreak strain of toxigenic V. cholerae O1 serotype Ogawa was isolated from freshwater and seafood samples. The cholera toxin gene was detected in harbor water samples.

We conducted a case-control study to investigate factors associated with epidemic cholera. Water treatment and handwashing may have been protective, highlighting the need for personal hygiene for cholera prevention in contaminated urban environments. We also found a diverse diet, a possible proxy for improved nutrition, was protective against cholera.

Cholera has affected humans for at least a millennium and persists as a major cause of illness and death worldwide, with recent epidemics in Zimbabwe (2008-2009) and Haiti (2010). Clinically, evidence exists of increasing severity of disease linked with emergence of atypical Vibrio cholerae organisms that have incorporated genetic material from classical biotype strains into an El Tor biotype background. A key element in transmission may be a recently recognized hyperinfectious phase, which persists for hours after passage in diarrheal feces. We propose a model of transmission in which environmental triggers (such as temperature) lead to increases in V. cholerae in environmental reservoirs, with spillover into human populations. However, once the microorganism is introduced into a human population, transmission occurs primary by "fast" transmission from person to person (taking advantage of the hyperinfectious state), without returning to the aquatic environment.

Cholera is rare in the United States (annual average 6 cases). Since epidemic cholera began in Hispaniola in 2010, a total of 23 cholera cases caused by toxigenic Vibrio cholerae O1 have been confirmed in the United States. Twenty-two case-patients reported travel to Hispaniola and 1 reported consumption of seafood from Haiti.

Purpose of Review: This review will focus on recent advances in our understanding of biologic and environmental factors that shape current cholera outbreaks, advances in our understanding of host-pathogen interactions during cholera, and recent evolution of current treatment and cholera prevention strategies., Recent Findings: New research studies have improved our understanding of a number of dynamic factors that shape the ecology of Vibrio cholerae and influence its transmission, including the role of lytic bacteriophage, biofilm formation, a hyperinfectious state of human-passaged V. cholerae, and the impact of severe weather events. Provision of safe water and improved sanitation continue to be the mainstays of preventing cholera transmission; however, the role of cholera vaccination as a control measure in both endemic and epidemic settings is evolving. Recent advances in our understanding of long-lived protective immunity after natural infection may aid in the global efforts to control cholera., Summary: Improved understanding of factors associated with protective immunity and dynamic factors associated with cholera outbreaks may lead to improved control and prevention strategies for cholera.

During August 2008-June 2009, an estimated 95,531 suspected cases of cholera and 4,282 deaths due to cholera were reported during the 2008 cholera outbreak in Zimbabwe. Despite the efforts by local and international organizations supported by the Zimbabwean Ministry of Health and Child Welfare in the establishment of cholera treatment centres throughout the country, the case-fatality rate (CFR) was much higher than expected. Over two-thirds of the deaths occurred in areas without access to treatment facilities, with the highest CFRs (>5%) reported from Masvingo, Manicaland, Mashonaland West, Mashonaland East, Midland, and Matabeleland North provinces. Some factors attributing to this high CFR included inappropriate cholera case management with inadequate use of oral rehydration therapy, inappropriate use of antibiotics, and a shortage of experienced healthcare professionals. The breakdown of both potable water and sanitation systems and the widespread contamination of available drinking-water sources were also considered responsible for the rapid and widespread distribution of the epidemic throughout the country. Training of healthcare professionals on appropriate cholera case management and implementation of recommended strategies to reduce the environmental contamination of drinking-water sources could have contributed to the progressive reduction in number of cases and deaths as observed at the end of February 2009.

In the mid-1800s, there was much debate about the origin or 'exciting cause' of cholera. Despite much confusion surrounding the disease, the so-called miasma theory emerged as the prevalent account about cholera's cause. Going against this mainstream view, the British physician John Snow inferred several things about cholera's origin and pathology that no one else inferred. Without observing the vibrio cholerae, however,-data unavailable to Snow and his colleagues-, there was no way of settling the question of what exactly was causing cholera and how, or if, it was passed on. The question then arises as to how Snow arrived at conclusions so systematically different from those of his opponents. In this paper, I want to look at Snow's reasoning in some detail, and show that there were certain principles, explanatory power in particular, that were epistemologically important to Snow in their own right. I will show that Snow himself takes explanatory power to be an epistemic property, and makes explicit links between explanatory power and confirmation. Systematically juxtaposing Snow's claims and his opponents', I will show that Snow was right to tout the explanatory power of his theory, and that his conclusions about the epistemic superiority of his theory over that of the miasmatists' were justified., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Background: Cholera has been a significant public health challenge in many communities. An outbreak of acute diarrheal illness occurred among participants in a wedding ceremony in a village in Qazvin, Iran, in 2008. We conducted an epidemiological, environmental and microbiological investigation to determine the causative agent, source and extent of this outbreak., Methods: Clinical and environmental samples were collected and analyzed for the presence of diarrhea-causing bacterial organisms, which included Vibrio cholera. The relationship between the strains was determined using enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR)., Results: The attack rate was 21.8%. Clinical and environmental samples were positive for V. cholerae serotype Inaba. All tested isolates had a similar ERIC-PCR pattern, which indicated that a single clone of V. cholerae was responsible for this outbreak., Conclusion: Our findings demonstrated that well water was the source of this outbreak.

Cholera, an acute gastro-intestinal infection and a waterborne disease continues to emerge in developing countries and remains an important global health challenge. We formulate a mathematical model that captures some essential dynamics of cholera transmission to study the impact of public health educational campaigns, vaccination and treatment as control strategies in curtailing the disease. The education-induced, vaccination-induced and treatment-induced reproductive numbers R(E), R(V), R(T) respectively and the combined reproductive number R(C) are compared with the basic reproduction number R(0) to assess the possible community benefits of these control measures. A Lyapunov functional approach is also used to analyse the stability of the equilibrium points. We perform sensitivity analysis on the key parameters that drive the disease dynamics in order to determine their relative importance to disease transmission and prevalence. Graphical representations are provided to qualitatively support the analytical results., (Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.)

Vibrio cholerae is a globally important pathogen that is endemic in many areas of the world and causes 3-5 million reported cases of cholera every year. Historically, there have been seven acknowledged cholera pandemics; recent outbreaks in Zimbabwe and Haiti are included in the seventh and ongoing pandemic. Only isolates in serogroup O1 (consisting of two biotypes known as 'classical' and 'El Tor') and the derivative O139 can cause epidemic cholera. It is believed that the first six cholera pandemics were caused by the classical biotype, but El Tor has subsequently spread globally and replaced the classical biotype in the current pandemic. Detailed molecular epidemiological mapping of cholera has been compromised by a reliance on sub-genomic regions such as mobile elements to infer relationships, making El Tor isolates associated with the seventh pandemic seem superficially diverse. To understand the underlying phylogeny of the lineage responsible for the current pandemic, we identified high-resolution markers (single nucleotide polymorphisms; SNPs) in 154 whole-genome sequences of globally and temporally representative V. cholerae isolates. Using this phylogeny, we show here that the seventh pandemic has spread from the Bay of Bengal in at least three independent but overlapping waves with a common ancestor in the 1950s, and identify several transcontinental transmission events. Additionally, we show how the acquisition of the SXT family of antibiotic resistance elements has shaped pandemic spread, and show that this family was first acquired at least ten years before its discovery in V. cholerae., (© 2011 Macmillan Publishers Limited. All rights reserved)

Cholera first appeared in North America (in Montreal and Quebec) in 1832 and spread rapidly across the eastern half of the continent. The dispatch of American disease control experts to Lower Canada in anticipation of cholera's spread implies that medical professionals expected spread, possibly from contagion, even though the notion that cholera was contagious was disparaged in medical writings of the time, and would be until John Snow's landmark work in London in the 1850s. Snow's insights derived largely from his observations on spatial and temporal patterns of cholera cases. We discuss a document from the 1832 epidemic, the report of Dr. Lewis Beck to New York's Governor Throop, which anticipates Snow in presenting geospatial data that imply cholera's contagiousness. Beck shows that the movements of immigrants along the newly completed New York state canal system resulted in sequential cholera outbreaks along the canal's path. Although aware of the degree to which this suggested contagion, Beck argues strenuously against the contagiousness of cholera. We explore the social context of early nineteenth-century medicine that probably led Beck to disbelieve his own observations, and to favor a medical model inconsistent with his data. Themes that emerge from our inquiry include belief in disease as a physical manifestation of defective morality, stigmatization of the poor and immigrant groups, and reluctance to overturn prevailing medical models that themselves reflected the economic position of medical practitioners. We show that these themes continue to serve as obstacles to innovation in medical and public health practice today.

With more than 250,000 cases and 4,000 deaths in the first 6 months, the cholera epidemic in Haiti has been one of the most explosive and deadly in recent history. It is also one of the best documented, with detailed surveillance information available from the beginning of the epidemic, which allowed its spread to all parts of the country to be traced. Piarroux et al. make good use of this information, along with their own careful field investigations, to trace the epidemic to its beginning and propose an explanation for its origins.

After onset of a cholera epidemic in Haiti in mid-October 2010, a team of researchers from France and Haiti implemented field investigations and built a database of daily cases to facilitate identification of communes most affected. Several models were used to identify spatiotemporal clusters, assess relative risk associated with the epidemic's spread, and investigate causes of its rapid expansion in Artibonite Department. Spatiotemporal analyses highlighted 5 significant clusters (p<0.001): 1 near Mirebalais (October 16-19) next to a United Nations camp with deficient sanitation, 1 along the Artibonite River (October 20-28), and 3 caused by the centrifugal epidemic spread during November. The regression model indicated that cholera more severely affected communes in the coastal plain (risk ratio 4.91) along the Artibonite River downstream of Mirebalais (risk ratio 4.60). Our findings strongly suggest that contamination of the Artibonite and 1 of its tributaries downstream from a military camp triggered the epidemic.

Global cholera incidence is increasing, particularly in sub-Saharan Africa. We examined the impact of climate and ocean environmental variability on cholera outbreaks, and developed a forecasting model for outbreaks in Zanzibar. Routine cholera surveillance reports between 1997 and 2006 were correlated with remotely and locally sensed environmental data. A seasonal autoregressive integrated moving average (SARIMA) model determined the impact of climate and environmental variability on cholera. The SARIMA model shows temporal clustering of cholera. A 1°C increase in temperature at 4 months lag resulted in a 2-fold increase of cholera cases, and an increase of 200 mm of rainfall at 2 months lag resulted in a 1.6-fold increase of cholera cases. Temperature and rainfall interaction yielded a significantly positive association (P < 0.04) with cholera at a 1-month lag. These results may be applied to forecast cholera outbreaks, and guide public health resources in controlling cholera in Zanzibar.

Cholera remains an important global cause of morbidity and mortality, capable of causing periodic epidemic disease. Beginning in August 2008, a major cholera epidemic occurred in Zimbabwe, with 98,585 reported cases and 4,287 deaths. The dynamics of such outbreaks, particularly in nonestuarine regions, are not well understood. We explored the utility of mathematical models in understanding transmission dynamics of cholera and in assessing the magnitude of interventions necessary to control epidemic disease. Weekly data on reported cholera cases were obtained from the Zimbabwe Ministry of Health and Child Welfare (MoHCW) for the period from November 13, 2008 to July 31, 2009. A mathematical model was formulated and fitted to cumulative cholera cases to estimate the basic reproductive numbers R(0) and the partial reproductive numbers from all 10 provinces for the 2008-2009 Zimbabwe cholera epidemic. Estimated basic reproductive numbers were highly heterogeneous, ranging from a low value of just above unity to 2.72. Partial reproductive numbers were also highly heterogeneous, suggesting that the transmission routes varied by province; human-to-human transmission accounted for 41-95% of all transmission. Our models suggest that the underlying patterns of cholera transmission varied widely from province to province, with a corresponding variation in the amenability of outbreaks in different provinces to control measures such as immunization. These data underscore the heterogeneity of cholera transmission dynamics, potentially linked to differences in environment, socio-economic conditions, and cultural practices. The lack of traditional estuarine reservoirs combined with these estimates of R(0) suggest that mass vaccination against cholera deployed strategically in Zimbabwe and surrounding regions could prevent future cholera epidemics and eventually eliminate cholera from the region.

Background: As resources are limited when responding to cholera outbreaks, knowledge about where to orient interventions is crucial. We describe the cholera epidemic affecting Guinea-Bissau in 2008 focusing on the geographical spread in order to guide prevention and control activities., Methodology/principal Findings: We conducted two studies: 1) a descriptive analysis of the cholera epidemic in Guinea-Bissau focusing on its geographical spread (country level and within the capital); and 2) a cross-sectional study to measure the prevalence of houses with at least one cholera case in the most affected neighbourhood of the capital (Bairro Bandim) to detect clustering of households with cases (cluster analysis). All cholera cases attending the cholera treatment centres in Guinea-Bissau who fulfilled a modified World Health Organization clinical case definition during the epidemic were included in the descriptive study. For the cluster analysis, a sample of houses was selected from a satellite photo (Google Earth™); 140 houses (and the four closest houses) were assessed from the 2,202 identified structures. We applied K-functions and Kernel smoothing to detect clustering. We confirmed the clustering using Kulldorff's spatial scan statistic. A total of 14,222 cases and 225 deaths were reported in the country (AR = 0.94%, CFR = 1.64%). The more affected regions were Biombo, Bijagos and Bissau (the capital). Bairro Bandim was the most affected neighborhood of the capital (AR = 4.0). We found at least one case in 22.7% of the houses (95%CI: 19.5-26.2) in this neighborhood. The cluster analysis identified two areas within Bairro Bandim at highest risk: a market and an intersection where runoff accumulates waste (p<0.001)., Conclusions/significance: Our analysis allowed for the identification of the most affected regions in Guinea-Bissau during the 2008 cholera outbreak, and the most affected areas within the capital. This information was essential for making decisions on where to reinforce treatment and to guide control and prevention activities.