Cholera epidemic in Guinea-Bissau (2008): the importance of "place"

Prevalence of diarrhoeal pathogens among children under five years of age with and without diarrhoea in Guinea-Bissau

BACKGROUND

Childhood diarrhoea, a major cause of morbidity and mortality in low-income regions, remains scarcely studied in many countries, such as Guinea-Bissau. Stool sample drying enables later qPCR analyses of pathogens without concern about electricity shortages.

METHODS

Dried stool samples of children under five years treated at the Bandim Health Centre in Bissau, Guinea-Bissau were screened by qPCR for nine enteric bacteria, five viruses, and four parasites. The findings of children having and not having diarrhoea were compared in age groups 0-11 and 12-59 months.

RESULTS

Of the 429 children- 228 with and 201 without diarrhoea- 96.9% and 93.5% had bacterial, 62.7% and 44.3% viral, and 52.6% and 48.3% parasitic pathogen findings, respectively. Enteroaggregarive Escherichia coli (EAEC; 60.5% versus 66.7%), enteropathogenic E. coli (EPEC; 61.4% versus 62.7%), Campylobacter (53.2% versus 51.8%), and enterotoxigenic E. coli (ETEC; 54.4% versus 44.3%) were the most common bacterial pathogens. Diarrhoea was associated with enteroinvasive E. coli (EIEC)/Shigella (63.3%), ETEC (54.4%), astrovirus (75.0%), norovirus GII (72.6%) and Cryptosporidium (71.2%). The only pathogen associated with severe diarrhoea was EIEC/Shigella (p<0.001). EAEC was found more frequent among the infants, and EIEC/Shigella, Giardia duodenalis and Dientamoeba fragilis among the older children.

CONCLUSIONS

Stool pathogens proved common among all the children regardless of them having diarrhoea or not.

Delineating and Analyzing Locality-Level Determinants of Cholera, Haiti

Centre Department, Haiti, was the origin of a major cholera epidemic during 2010–2019. Although no fine-scale spatial delineation is officially available, we aimed to analyze determinants of cholera at the local level and identify priority localities in need of interventions. After estimating the likely boundaries of 1,730 localities by using Voronoi polygons, we mapped 5,322 suspected cholera cases reported during January 2015–September 2016 by locality alongside environmental and socioeconomic variables. A hierarchical clustering on principal components highlighted 2 classes with high cholera risk: localities close to rivers and unimproved water sources (standardized incidence ratio 1.71, 95% CI 1.02–2.87; p = 0.04) and urban localities with markets (standardized incidence ratio 1.69, 95% CI 1.25–2.29; p = 0.0006). Our analyses helped identify and characterize areas where efforts should be focused to reduce vulnerability to cholera and other waterborne diseases; these methods could be used in other contexts.

Licensed and Recommended Inactivated Oral CholeraVaccines: From Development to Innovative Deployment

Cholera is a disease of poverty and occurs where there is a lack of access to clean water and adequate sanitation. Since improved water supply and sanitation infrastructure cannot be implemented immediately in many high-risk areas, vaccination against cholera is an important additional tool for prevention and control. We describe the development of licensed and recommended inactivated oral cholera vaccines (OCVs), including the results of safety, efficacy and effectiveness studies and the creation of the global OCV stockpile. Over the years, the public health strategy for oral cholera vaccination has broadened-from purely pre-emptive use to reactive deployment to help control outbreaks. Limited supplies of OCV doses continues to be an important problem. We discuss various innovative dosing and delivery approaches that have been assessed and implemented and evidence of herd protection conferred by OCVs. We expect that the demand for OCVs will continue to increase in the coming years across many countries.

Early detection of cholera epidemics to support control in fragile states: estimation of delays and potential epidemic sizes

BACKGROUND

Cholera epidemics continue to challenge disease control, particularly in fragile and conflict-affected states. Rapid detection and response to small cholera clusters is key for efficient control before an epidemic propagates. To understand the capacity for early response in fragile states, we investigated delays in outbreak detection, investigation, response, and laboratory confirmation, and we estimated epidemic sizes. We assessed predictors of delays, and annual changes in response time.

METHODS

We compiled a list of cholera outbreaks in fragile and conflict-affected states from 2008 to 2019. We searched for peer-reviewed articles and epidemiological reports. We evaluated delays from the dates of symptom onset of the primary case, and the earliest dates of outbreak detection, investigation, response, and confirmation. Information on how the outbreak was alerted was summarized. A branching process model was used to estimate epidemic size at each delay. Regression models were used to investigate the association between predictors and delays to response.

RESULTS

Seventy-six outbreaks from 34 countries were included. Median delays spanned 1-2 weeks: from symptom onset of the primary case to presentation at the health facility (5 days, IQR 5-5), detection (5 days, IQR 5-6), investigation (7 days, IQR 5.8-13.3), response (10 days, IQR 7-18), and confirmation (11 days, IQR 7-16). In the model simulation, the median delay to response (10 days) with 3 seed cases led to a median epidemic size of 12 cases (upper range, 47) and 8% of outbreaks ≥ 20 cases (increasing to 32% with a 30-day delay to response). Increased outbreak size at detection (10 seed cases) and a 10-day median delay to response resulted in an epidemic size of 34 cases (upper range 67 cases) and < 1% of outbreaks < 20 cases. We estimated an annual global decrease in delay to response of 5.2% (95% CI 0.5-9.6, p = 0.03). Outbreaks signaled by immediate alerts were associated with a reduction in delay to response of 39.3% (95% CI 5.7-61.0, p = 0.03).

CONCLUSIONS

From 2008 to 2019, median delays from symptom onset of the primary case to case presentation and to response were 5 days and 10 days, respectively. Our model simulations suggest that depending on the outbreak size (3 versus 10 seed cases), in 8 to 99% of scenarios, a 10-day delay to response would result in large clusters that would be difficult to contain. Improving the delay to response involves rethinking the integration at local levels of event-based detection, rapid diagnostic testing for cluster validation, and integrated alert, investigation, and response.

Quality Assessment of Three Types of Drinking Water Sources in Guinea-Bissau

The lack of access to safe drinking water causes important health problems, mainly in developing countries. In the West African country Guinea-Bissau, waterborne diseases are recognised by WHO as major infectious diseases. This study analysed the microbiological and physicochemical parameters of drinking water in the capital Bissau and its surroundings. Twenty-two sites belonging to different water sources (piped water, tubewells and shallow wells) were surveyed twice a day for three weeks, in both dry and wet seasons. Most of the microbiological parameters were out of the acceptable ranges in all types of water and both seasons and tended to worsen in the wet season. Moreover, in Bissau, the levels of faecal contamination in piped water increased from the holes to the consumer (tap/fountain). Several physicochemical variables showed values out of the internationally accepted ranges. Both well sources showed low-pH water (4.87–5.59), with high nitrite and iron levels in the wet season and high hexavalent chromium concentration in the dry season. The residual chlorine never reached the minimum recommended level in any of the water sources or seasons, suggesting a high risk of contamination. Results reveal a lack of quality in the three water sources analysed, coherent with the high number of diarrheal cases in the country. There is an urgent need to improve sanitarian conditions to reduce the disease burden caused by these waterborne illnesses.

Feasibility of a Comprehensive Targeted Cholera Intervention in The Kathmandu Valley, Nepal

A comprehensive targeted intervention (CTI) was designed and deployed in the neighborhoods of cholera cases in the Kathmandu Valley with the intent of reducing rates among the neighbors of the case. This was a feasibility study to determine whether clinical centers, laboratories, and field teams were able to mount a rapid, community-based response to a case within 2 days of hospital admission. Daily line listings were requested from 15 participating hospitals during the monsoon season, and a single case initiated the CTI. A standard case definition was used: acute watery diarrhea, with or without vomiting, in a patient aged 1 year or older. Rapid diagnostic tests and bacterial culture were used for confirmation. The strategy included household investigation of cases; water testing; water, sanitation, and hygiene (WASH) intervention; and health education. A CTI coverage survey was conducted 8 months postintervention. From June to December of 2016, 169 cases of Vibrio cholerae O1 were confirmed by bacterial culture. Average time to culture result was 3 days. On average, the CTI Rapid Response Team (RRT) was able to visit households 1.7 days after the culture result was received from the hospital (3.9 days from hospital admission). Coverage of WASH and health behavior messaging campaigns were 30.2% in the target areas. Recipients of the intervention were more likely to have knowledge of cholera symptoms, treatment, and prevention than non-recipients. Although the RRT were able to investigate cases at the household within 2 days of a positive culture result, the study identified several constraints that limited a truly rapid response.

Individual and Household Risk Factors for Symptomatic Cholera Infection: A Systematic Review and Meta-analysis

Background

Cholera has caused 7 global pandemics, including the current one which has been ongoing since 1961. A systematic review of risk factors for symptomatic cholera infection has not been previously published.

Methods

In accordance with PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, we performed a systematic review and meta-analysis of individual and household risk factors for symptomatic cholera infection.

Results

We identified 110 studies eligible for inclusion in qualitative synthesis. Factors associated with symptomatic cholera that were eligible for meta-analysis included education less than secondary level (summary odds ratio [SOR], 2.64; 95% confidence interval [CI], 1.41-4.92; I2 = 8%), unimproved water source (SOR, 3.48; 95% CI, 2.18-5.54; I2 = 77%), open container water storage (SOR, 2.03; 95% CI, 1.09-3.76; I2 = 62%), consumption of food outside the home (SOR, 2.76; 95% CI, 1.62-4.69; I2 = 64%), household contact with cholera (SOR, 2.91; 95% CI, 1.62-5.25; I2 = 89%), water treatment (SOR, 0.37; 95% CI, .21-.63; I2 = 74%), and handwashing (SOR, 0.29; 95% CI, .20-.43; I2 = 37%). Other notable associations with symptomatic infection included income/wealth, blood group, gastric acidity, infant breastfeeding status, and human immunodeficiency virus infection.

Conclusions

We identified potential risk factors for symptomatic cholera infection including environmental characteristics, socioeconomic factors, and intrinsic patient factors. Ultimately, a combination of interventional approaches targeting various groups with risk-adapted intensities may prove to be the optimal strategy for cholera control.

The case for ring vaccinations with special consideration of oral cholera vaccines

Ring vaccinations create a zone of immune contacts around a case to prevent further disease transmission and have been successfully employed in the eradication of smallpox and the control of other infections. Millions of oral cholera vaccine (OCV) doses have been effectively deployed through mass vaccination campaigns. But there are situations when the OCV supply, resources, and time are limited and alternative strategies need to be considered. People living in close proximity of cholera cases often share risk factors such as contaminated water supply and poor sanitation. Targeting people within a given radius around a cholera case for intervention including vaccination, improved water supply and sanitation may be a practical and effective approach. A ring oral cholera vaccination strategy could be considered before, after or as an alternative to a mass vaccination approach. We review here the use of the ring vaccinations in general and specifically during cholera outbreaks.

Characteristics of human encounters and social mixing patterns relevant to infectious diseases spread by close contact: a survey in Southwest Uganda

Background

Quantification of human interactions relevant to infectious disease transmission through social contact is central to predict disease dynamics, yet data from low-resource settings remain scarce.

Methods

We undertook a social contact survey in rural Uganda, whereby participants were asked to recall details about the frequency, type, and socio-demographic characteristics of any conversational encounter that lasted for ≥5 min (henceforth defined as ‘contacts’) during the previous day. An estimate of the number of ‘casual contacts’ (i.e. < 5 min) was also obtained.

Results

In total, 566 individuals were included in the study. On average participants reported having routine contact with 7.2 individuals (range 1-25). Children aged 5-14 years had the highest frequency of contacts and the elderly (≥65 years) the fewest (P < 0.001). A strong age-assortative pattern was seen, particularly outside the household and increasingly so for contacts occurring further away from home. Adults aged 25-64 years tended to travel more often and further than others, and males travelled more frequently than females.

Conclusion

Our study provides detailed information on contact patterns and their spatial characteristics in an African setting. It therefore fills an important knowledge gap that will help more accurately predict transmission dynamics and the impact of control strategies in such areas.

Electronic supplementary material

The online version of this article (10.1186/s12879-018-3073-1) contains supplementary material, which is available to authorized users.

Dynamics of cholera epidemics from Benin to Mauritania

Background

The countries of West Africa are largely portrayed as cholera endemic, although the dynamics of outbreaks in this region of Africa remain largely unclear.

Methodology/Principal findings

To understand the dynamics of cholera in a major portion of West Africa, we analyzed cholera epidemics from 2009 to 2015 from Benin to Mauritania. We conducted a series of field visits as well as multilocus variable tandem repeat analysis and whole-genome sequencing analysis of V. cholerae isolates throughout the study region. During this period, Ghana accounted for 52% of the reported cases in the entire study region (coastal countries from Benin to Mauritania). From 2009 to 2015, we found that one major wave of cholera outbreaks spread from Accra in 2011 northwestward to Sierra Leone and Guinea in 2012. Molecular epidemiology analysis confirmed that the 2011 Ghanaian isolates were related to those that seeded the 2012 epidemics in Guinea and Sierra Leone. Interestingly, we found that many countries deemed “cholera endemic” actually suffered very few outbreaks, with multi-year lulls.

Conclusions/Significance

This study provides the first cohesive vision of the dynamics of cholera epidemics in a major portion of West Africa. This epidemiological overview shows that from 2009 to 2015, at least 54% of reported cases concerned populations living in the three urban areas of Accra, Freetown, and Conakry. These findings may serve as a guide to better target cholera prevention and control efforts in the identified cholera hotspots in West Africa.

We analyzed cholera epidemics from Benin to Mauritania, during 2009 to 2015, and performed a series of field visits as well as molecular epidemiology analyses of V. cholerae isolates from most recent epidemics throughout West Africa. We found that at least 54% of cases concerned populations living in the three urban areas of Accra, Freetown, and Conakry. Accra, Ghana represented the main cholera hotspot in the entire study region. Our findings indicate that the water network system in Accra may play a role in the rapid diffusion of cholera throughout the city. As observed in Accra, Conakry, and Freetown, once cholera cases arrive in overpopulated urban settings with poor sanitation, increased rainfall facilitated the contamination of unprotected water sources with human waste from cholera patients, thus promoting a rapid increase in cholera incidence. To more efficiently and effectively combat cholera in West Africa, these findings may serve as a guide to better target cholera prevention and control interventions.

The potential impact of case-area targeted interventions in response to cholera outbreaks: A modeling study

BACKGROUND

Cholera prevention and control interventions targeted to neighbors of cholera cases (case-area targeted interventions [CATIs]), including improved water, sanitation, and hygiene, oral cholera vaccine (OCV), and prophylactic antibiotics, may be able to efficiently avert cholera cases and deaths while saving scarce resources during epidemics. Efforts to quickly target interventions to neighbors of cases have been made in recent outbreaks, but little empirical evidence related to the effectiveness, efficiency, or ideal design of this approach exists. Here, we aim to provide practical guidance on how CATIs might be used by exploring key determinants of intervention impact, including the mix of interventions, "ring" size, and timing, in simulated cholera epidemics fit to data from an urban cholera epidemic in Africa.

METHODS AND FINDINGS

We developed a micro-simulation model and calibrated it to both the epidemic curve and the small-scale spatiotemporal clustering pattern of case households from a large 2011 cholera outbreak in N'Djamena, Chad (4,352 reported cases over 232 days), and explored the potential impact of CATIs in simulated epidemics. CATIs were implemented with realistic logistical delays after cases presented for care using different combinations of prophylactic antibiotics, OCV, and/or point-of-use water treatment (POUWT) starting at different points during the epidemics and targeting rings of various radii around incident case households. Our findings suggest that CATIs shorten the duration of epidemics and are more resource-efficient than mass campaigns. OCV was predicted to be the most effective single intervention, followed by POUWT and antibiotics. CATIs with OCV started early in an epidemic focusing on a 100-m radius around case households were estimated to shorten epidemics by 68% (IQR 62% to 72%), with an 81% (IQR 69% to 87%) reduction in cases compared to uncontrolled epidemics. These same targeted interventions with OCV led to a 44-fold (IQR 27 to 78) reduction in the number of people needed to target to avert a single case of cholera, compared to mass campaigns in high-cholera-risk neighborhoods. The optimal radius to target around incident case households differed by intervention type, with antibiotics having an optimal radius of 30 m to 45 m compared to 70 m to 100 m for OCV and POUWT. Adding POUWT or antibiotics to OCV provided only marginal impact and efficiency improvements. Starting CATIs early in an epidemic with OCV and POUWT targeting those within 100 m of an incident case household reduced epidemic durations by 70% (IQR 65% to 75%) and the number of cases by 82% (IQR 71% to 88%) compared to uncontrolled epidemics. CATIs used late in epidemics, even after the peak, were estimated to avert relatively few cases but substantially reduced the number of epidemic days (e.g., by 28% [IQR 15% to 45%] for OCV in a 100-m radius). While this study is based on a rigorous, data-driven approach, the relatively high uncertainty about the ways in which POUWT and antibiotic interventions reduce cholera risk, as well as the heterogeneity in outbreak dynamics from place to place, limits the precision and generalizability of our quantitative estimates.

CONCLUSIONS

In this study, we found that CATIs using OCV, antibiotics, and water treatment interventions at an appropriate radius around cases could be an effective and efficient way to fight cholera epidemics. They can provide a complementary and efficient approach to mass intervention campaigns and may prove particularly useful during the initial phase of an outbreak, when there are few cases and few available resources, or in order to shorten the often protracted tails of cholera epidemics.

Identifying cholera "hotspots" in Uganda: An analysis of cholera surveillance data from 2011 to 2016

BACKGROUND

Despite advance in science and technology for prevention, detection and treatment of cholera, this infectious disease remains a major public health problem in many countries in sub-Saharan Africa, Uganda inclusive. The aim of this study was to identify cholera hotspots in Uganda to guide the development of a roadmap for prevention, control and elimination of cholera in the country.

METHODOLOGY/PRINCIPLE FINDINGS

We obtained district level confirmed cholera outbreak data from 2011 to 2016 from the Ministry of Health, Uganda. Population and rainfall data were obtained from the Uganda Bureau of Statistics, and water, sanitation and hygiene data from the Ministry of Water and Environment. A spatial scan test was performed to identify the significantly high risk clusters. Cholera hotspots were defined as districts whose center fell within a significantly high risk cluster or where a significantly high risk cluster was completely superimposed onto a district. A zero-inflated negative binomial regression model was employed to identify the district level risk factors for cholera. In total 11,030 cases of cholera were reported during the 6-year period. 37(33%) of 112 districts reported cholera outbreaks in one of the six years, and 20 (18%) districts experienced cholera at least twice in those years. We identified 22 districts as high risk for cholera, of which 13 were near a border of Democratic Republic of Congo (DRC), while 9 districts were near a border of Kenya. The relative risk of having cholera inside the high-risk districts (hotspots) were 2 to 22 times higher than elsewhere in the country. In total, 7 million people were within cholera hotspots. The negative binomial component of the ZINB model shows people living near a lake or the Nile river were at increased risk for cholera (incidence rate ratio, IRR = 0.98, 95% CI: 0.97 to 0.99, p < .01); people living near the border of DRC/Kenya or higher incidence rate in the neighboring districts were increased risk for cholera in a district (IRR = 0.99, 95% CI: 0.98 to 1.00, p = .02 and IRR = 1.02, 95% CI: 1.01 to 1.03, p < .01, respectively). The zero inflated component of the ZINB model yielded shorter distance to Kenya or DRC border, higher incidence rate in the neighboring districts, and higher annual rainfall in the district were associated with the risk of having cholera in the district.

CONCLUSIONS/SIGNIFICANCE

The study identified cholera hotspots during the period 2011-2016. The people located near the international borders, internationally shared lakes and river Nile were at higher risk for cholera outbreaks than elsewhere in the country. Targeting cholera interventions to these locations could prevent and ultimately eliminate cholera in Uganda.

Identification of burden hotspots and risk factors for cholera in India: An observational study

Background

Even though cholera has existed for centuries and many parts of the country have sporadic, endemic and epidemic cholera, it is still an under-recognized health problem in India. A Cholera Expert Group in the country was established to gather evidence and to prepare a road map for control of cholera in India. This paper identifies cholera burden hotspots and factors associated with an increased risk of the disease.

Methodology/Principle findings

We acquired district level data on cholera case reports of 2010–2015 from the Integrated Disease Surveillance Program. Socioeconomic characteristics and coverage of water and sanitation was obtained from the 2011 census. Spatial analysis was performed to identify cholera hotspots, and a zero-inflated Poisson regression was employed to identify the factors associated with cholera and predicted case count in the district. 27,615 cholera cases were reported during the 6-year period. Twenty-four of 36 states of India reported cholera during these years, and 13 states were classified as endemic. Of 641 districts, 78 districts in 15 states were identified as “hotspots” based on the reported cases. On the other hand, 111 districts in nine states were identified as “hotspots” from model-based predicted number of cases. The risk for cholera in a district was negatively associated with the coverage of literate persons, households using treated water source and owning mobile telephone, and positively associated with the coverage of poor sanitation and drainage conditions and urbanization level in the district.

Conclusions/Significance

The study reaffirms that cholera continues to occur throughout a large part of India and identifies the burden hotspots and risk factors. Policymakers may use the findings of the article to develop a roadmap for prevention and control of cholera in India.

Epidemiological placism in public health emergencies: Ebola in two Dallas neighborhoods

Super-diverse cities face distinctive challenges during infectious disease outbreaks. For refugee and immigrant groups from epidemic source locations, identities of place blend with epidemiological logics in convoluted ways during these crises. This research investigated the relationships of place and stigma during the Dallas Ebola crisis. Ethnographic results illustrate how Africanness, more than neighborhood stigma, informed Dallas residents' experience of stigma. The problems of place-based stigma, the imprecision of epidemiological placism, and the cohesion of stigma to semiotically powerful levels of place - rather than to realistic risk categories - are discussed. Taking its authority from epidemiology, placism is an important source of potential stigma with critical implications for the success of public health messaging.

Rapid dipstick detection of Vibrio cholerae in household stored and municipal water in Dhaka, Bangladesh: CHoBI7 trial

OBJECTIVE

In urban Dhaka, Bangladesh, 30% of source water samples collected from the households of patients with cholera had detectable Vibrio cholerae. These findings indicate an urgent need for a public health intervention for this population. The Crystal VC^® dipstick test is a rapid method for detecting V. cholerae in stool and water. However, to date no study has investigated the use of the rapid dipstick test for household surveillance of stored drinking water.

METHODS

The efficacy of the Crystal VC^® dipstick test for detecting V. cholerae in the Dhaka city municipal water supply and stored household drinking water sources after enrichment for 18 h in alkaline peptone water (APW) was compared to bacterial culture as the gold standard.

RESULTS

A total of 1648 water samples (824 stored household drinking water samples and 824 municipal water supply samples) were collected from households of patients with cholera. The overall specificity and sensitivity of the dipstick test compared to bacterial culture was 99.6% (95% confidence interval (CI): 99.2%, 99.9%) and 65.6% (95% CI: 55.2%, 75%), respectively. The specificities for stored household drinking water and Dhaka city municipal supply water compared to bacterial culture were 99.8% (95% CI: 99.1%, 100%) and 99.5% (95% CI: 98.6%, 99.9%), respectively (P = 0.138), and the sensitivities were 66.7% (95% CI: 43.0%, 85.4%) and 65.3% (95% CI: 53.5%, 76.0%), respectively (P = 0.891).

CONCLUSION

The Crystal VC^® dipstick is a promising screening tool for cholera outbreak surveillance in resource-limited settings where elimination of false-positive results is critical. The lower than expected sensitivity should be further investigated in future studies.

Potential for Controlling Cholera Using a Ring Vaccination Strategy: Re-analysis of Data from a Cluster-Randomized Clinical Trial

INTRODUCTION

Vaccinating a buffer of individuals around a case (ring vaccination) has the potential to target those who are at highest risk of infection, reducing the number of doses needed to control a disease. We explored the potential vaccine effectiveness (VE) of oral cholera vaccines (OCVs) for such a strategy.

METHODS AND FINDINGS

This analysis uses existing data from a cluster-randomized clinical trial in which OCV or placebo was given to 71,900 participants in Kolkata, India, from 27 July to 10 September 2006. Cholera surveillance was then conducted on 144,106 individuals living in the study area, including trial participants, for 5 y following vaccination. First, we explored the risk of cholera among contacts of cholera patients, and, second, we measured VE among individuals living within 25 m of cholera cases between 8 and 28 d after onset of the index case. For the first analysis, individuals living around each index case identified during the 5-y period were assembled using a ring to define cohorts of individuals exposed to cholera index cases. An index control without cholera was randomly selected for each index case from the same population, matched by age group, and individuals living around each index control were assembled using a ring to define cohorts not exposed to cholera cases. Cholera attack rates among the exposed and non-exposed cohorts were compared using different distances from the index case/control to define the rings and different time frames to define the period at risk. For the VE analysis, the exposed cohorts were further stratified according to the level of vaccine coverage into high and low coverage strata. Overall VE was assessed by comparing the attack rates between high and low vaccine coverage strata irrespective of individuals' vaccination status, and indirect VE was assessed by comparing the attack rates among unvaccinated members between high and low vaccine coverage strata. Cholera risk among the cohort exposed to cholera cases was 5-11 times higher than that among the cohort not exposed to cholera cases. The risk gradually diminished with an increase in distance and time. The overall and indirect VE measured between 8 and 28 d after exposure to a cholera index case during the first 2 y was 91% (95% CI 62%-98%) and 93% (95% CI 44%-99%), respectively. VE persisted for 5 y after vaccination and was similar whether the index case was a young child (<5 y) or was older. Of note, this study was a reanalysis of a cholera vaccine trial that used two doses; thus, a limitation of the study relates to the assumption that a single dose, if administered quickly, will induce a similar level of total and indirect protection over the short term as did two doses.

CONCLUSIONS

These findings suggest that high-level protection can be achieved if individuals living close to cholera cases are living in a high coverage ring. Since this was an observational study including participants who had received two doses of vaccine (or placebo) in the clinical trial, further studies are needed to determine whether a ring vaccination strategy, in which vaccine is given quickly to those living close to a case, is feasible and effective.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00289224.

Near real-time space-time cluster analysis for detection of enteric disease outbreaks in a community setting

OBJECTIVES

To enhance timely surveillance of bacterial enteric pathogens, space-time cluster analysis was introduced in Israel in May 2013.

METHODS

Stool isolation data of Salmonella, Shigella, and Campylobacter from patients of a large Health Maintenance Organization were analyzed weekly by ArcGIS and SaTScan, and cluster results were sent promptly to local departments of health (LDOHs).

RESULTS

During eighteen months, we identified 52 Shigella sonnei clusters, two Salmonella clusters, and no Campylobacter clusters. S. sonnei clusters lasted from one to 33 days and included three to 30 individuals. Thirty-one (60%) of the S. sonnei clusters were known to LDOHs prior to cluster analysis. Clusters not previously known by the LDOHs prompted epidemiologic investigations. In 31 of the 37 (84%) confirmed clusters, educational institutes (nursery schools, kindergartens, and a primary school) were involved.

CONCLUSIONS

Cluster analysis demonstrated capability to complement enteric disease surveillance. Scaling up the system can further enhance timely detection and control of outbreaks.

Detection and Quantification of Vibrio cholerae, Vibrio parahaemolyticus, and Vibrio vulnificus in Coastal Waters of Guinea-Bissau (West Africa)

V. cholerae, V. parahaemolyticus, and V. vulnificus are recognized human pathogens. Although several studies are available worldwide, both on environmental and clinical contexts, little is known about the ecology of these vibrios in African coastal waters. In this study, their co-occurrence and relationships to key environmental constraints in the coastal waters of Guinea-Bissau were examined using the most probable number-polymerase chain reaction (MPN-PCR) approach. All Vibrio species were universally detected showing higher concentrations by the end of the wet season. The abundance of V. cholerae (ISR 16S-23S rRNA) ranged 0-1.2 × 10(4) MPN/L, whereas V. parahaemolyticus (toxR) varied from 47.9 to 1.2 × 10(5) MPN/L. Although the presence of genotypes associated with virulence was found in environmental V. cholerae isolates, ctxA+ V. cholerae was detected, by MPN-PCR, only on two occasions. Enteropathogenic (tdh+ and trh+) V. parahaemolyticus were detected at concentrations up to 1.2 × 10(3) MPN/L. V. vulnificus (vvhA) was detected simultaneously in all surveyed sites only at the end of the wet season, with maximum concentrations of 1.2 × 10(5) MPN/L. Our results suggest that sea surface water temperature and salinity were the major environmental controls to all Vibrio species. This study represents the first detection and quantification of co-occurring Vibrio species in West African coastal waters, highlighting the potential health risk associated with the persistence of human pathogenic Vibrio species.

Spatial methods for infectious disease outbreak investigations: systematic literature review

Investigations of infectious disease outbreaks are conventionally framed in terms of person, time and place. Although geographic information systems have increased the range of tools available, spatial analyses are used relatively infrequently. We conducted a systematic review of published reports of outbreak investigations worldwide to estimate the prevalence of spatial methods, describe the techniques applied and explore their utility. We identified 80 reports using spatial methods published between 1979 and 2013, ca 0.4% of the total number of published outbreaks. Environmental or waterborne infections were the most commonly investigated, and most reports were from the United Kingdom. A range of techniques were used, including simple dot maps, cluster analyses and modelling approaches. Spatial tools were usefully applied throughout investigations, from initial confirmation of the outbreak to describing and analysing cases and communicating findings. They provided valuable insights that led to public health actions, but there is scope for much wider implementation and development of new methods.

Micro-scale Spatial Clustering of Cholera Risk Factors in Urban Bangladesh

Close interpersonal contact likely drives spatial clustering of cases of cholera and diarrhea, but spatial clustering of risk factors may also drive this pattern. Few studies have focused specifically on how exposures for disease cluster at small spatial scales. Improving our understanding of the micro-scale clustering of risk factors for cholera may help to target interventions and power studies with cluster designs. We selected sets of spatially matched households (matched-sets) near cholera case households between April and October 2013 in a cholera endemic urban neighborhood of Tongi Township in Bangladesh. We collected data on exposures to suspected cholera risk factors at the household and individual level. We used intra-class correlation coefficients (ICCs) to characterize clustering of exposures within matched-sets and households, and assessed if clustering depended on the geographical extent of the matched-sets. Clustering over larger spatial scales was explored by assessing the relationship between matched-sets. We also explored whether different exposures tended to appear together in individuals, households, and matched-sets. Household level exposures, including: drinking municipal supplied water (ICC = 0.97, 95%CI = 0.96, 0.98), type of latrine (ICC = 0.88, 95%CI = 0.71, 1.00), and intermittent access to drinking water (ICC = 0.96, 95%CI = 0.87, 1.00) exhibited strong clustering within matched-sets. As the geographic extent of matched-sets increased, the concordance of exposures within matched-sets decreased. Concordance between matched-sets of exposures related to water supply was elevated at distances of up to approximately 400 meters. Household level hygiene practices were correlated with infrastructure shown to increase cholera risk. Co-occurrence of different individual level exposures appeared to mostly reflect the differing domestic roles of study participants. Strong spatial clustering of exposures at a small spatial scale in a cholera endemic population suggests a possible role for highly targeted interventions. Studies with cluster designs in areas with strong spatial clustering of exposures should increase sample size to account for the correlation of these exposures.

While clustering of cholera incidence had been previously described, the relative role of similar risk behaviors versus transmission dynamics is not well understood. We explored how risk factors for cholera clustered at the sub-community scale, and found significant more correlation in risk behaviors among spatially matched households than the community as a whole. We found clustering of single risk factors, and co-occurrence of different risk factors. Our results indicated that the distribution of risk behaviors may play a role in the clustering of cholera cases at very small (e.g., <100m) spatial scales. This had implications for spatially matched study designs, which may be overmatching on some exposures. It also may lead us to rethink targeted interventions, suggesting a role for more intensive highly targeted interventions as a supplement to more generalized campaigns.

Childhood Diarrhea Exhibits Spatiotemporal Variation in Northwest Ethiopia: A SaTScan Spatial Statistical Analysis

BACKGROUND

Childhood diarrhea continues to be a public health problem in developing countries, including Ethiopia. Detecting clusters and trends of childhood diarrhea is important to designing effective interventions. Therefore, this study aimed to investigate spatiotemporal clustering and seasonal variability of childhood diarrhea in northwest Ethiopia.

METHODS

Retrospective record review of childhood diarrhea was conducted using quarterly reported data to the district health office for the seven years period beginning July 1, 2007. Thirty three districts were included and geo-coded in this study. Spatial, temporal and space-time scan spatial statistics were employed to identify clusters of childhood diarrhea. Smoothing using a moving average was applied to visualize the trends and seasonal pattern of childhood diarrhea. Statistical analyses were performed using Excel® and SaTScan programs. The maps were plotted using ArcGIS 10.0.

RESULTS

Childhood diarrhea in northwest Ethiopia exhibits statistical evidence of spatial, temporal, and spatiotemporal clustering, with seasonal patterns and decreasing temporal trends observed in the study area. A most likely purely spatial cluster was found in the East Gojjam administrative zone of Gozamin district (LLR = 7123.89, p <0.001). The most likely spatiotemporal cluster was detected in all districts of East Gojjam zone and a few districts of the West Gojjam zone (LLR = 24929.90, p<0.001), appearing from July 1, 2009 to June 30, 2011. One high risk period from July 1, 2008 to June 30, 2010 (LLR = 9655.86, p = 0.001) was observed in all districts. Peak childhood diarrhea cases showed a seasonal trend, occurring more frequently from January to March and April to June.

CONCLUSION

Childhood diarrhea did not occur at random. It has spatiotemporal variation and seasonal patterns with a decreasing temporal trend. Accounting for the spatiotemporal variation identified in the study areas is advised for the prevention and control of diarrhea.

The Impact of a One-Dose versus Two-Dose Oral Cholera Vaccine Regimen in Outbreak Settings: A Modeling Study

BACKGROUND

In 2013, a stockpile of oral cholera vaccine (OCV) was created for use in outbreak response, but vaccine availability remains severely limited. Innovative strategies are needed to maximize the health impact and minimize the logistical barriers to using available vaccine. Here we ask under what conditions the use of one dose rather than the internationally licensed two-dose protocol may do both.

METHODS AND FINDINGS

Using mathematical models we determined the minimum relative single-dose efficacy (MRSE) at which single-dose reactive campaigns are expected to be as or more effective than two-dose campaigns with the same amount of vaccine. Average one- and two-dose OCV effectiveness was estimated from published literature and compared to the MRSE. Results were applied to recent outbreaks in Haiti, Zimbabwe, and Guinea using stochastic simulations to illustrate the potential impact of one- and two-dose campaigns. At the start of an epidemic, a single dose must be 35%-56% as efficacious as two doses to avert the same number of cases with a fixed amount of vaccine (i.e., MRSE between 35% and 56%). This threshold decreases as vaccination is delayed. Short-term OCV effectiveness is estimated to be 77% (95% CI 57%-88%) for two doses and 44% (95% CI -27% to 76%) for one dose. This results in a one-dose relative efficacy estimate of 57% (interquartile range 13%-88%), which is above conservative MRSE estimates. Using our best estimates of one- and two-dose efficacy, we projected that a single-dose reactive campaign could have prevented 70,584 (95% prediction interval [PI] 55,943-86,205) cases in Zimbabwe, 78,317 (95% PI 57,435-100,150) in Port-au-Prince, Haiti, and 2,826 (95% PI 2,490-3,170) cases in Conakry, Guinea: 1.1 to 1.2 times as many as a two-dose campaign. While extensive sensitivity analyses were performed, our projections of cases averted in past epidemics are based on severely limited single-dose efficacy data and may not fully capture uncertainty due to imperfect surveillance data and uncertainty about the transmission dynamics of cholera in each setting.

CONCLUSIONS

Reactive vaccination campaigns using a single dose of OCV may avert more cases and deaths than a standard two-dose campaign when vaccine supplies are limited, while at the same time reducing logistical complexity. These findings should motivate consideration of the trade-offs between one- and two-dose campaigns in resource-constrained settings, though further field efficacy data are needed and should be a priority in any one-dose campaign.

Spatial analysis of childhood cancer: a case/control study

Background

Childhood cancer was the leading cause of death among children aged 1-14 years for 2012 in Spain. Leukemia has the highest incidence, followed by tumors of the central nervous system (CNS) and lymphomas (Hodgkin lymphoma, HL, and Non-Hodgkin’s lymphoma, NHL). Spatial distribution of childhood cancer cases has been under concern with the aim of identifying potential risk factors.

Objective

The two objectives are to study overall spatial clustering and cluster detection of cases of the three main childhood cancer causes, looking to increase etiological knowledge.

Methods

We ran a case-control study. The cases were children aged 0 to 14 diagnosed with leukemia, lymphomas (HL and NHL) or CNS neoplasm in five Spanish regions for the period 1996-2011. As a control group, we used a sample from the Birth Registry matching every case by year of birth, autonomous region of residence and sex with six controls. We geocoded and validated the address of the cases and controls. For our two objectives we used two different methodologies. For the first, for overall spatial clustering detection, we used the differences of K functions from the spatial point patterns perspective proposed by Diggle and Chetwynd and the second, for cluster detection, we used the spatial scan statistic proposed by Kulldorff with a level for statistical significance of 0.05.

Results

We had 1062 cases of leukemia, 714 cases of CNS, 92 of HL and 246 of NHL. Accordingly we had 6 times the number of controls, 6372 controls for leukemia, 4284 controls for CNS, 552 controls for HL and 1476 controls for NHL. We found variations in the estimated empirical D(s) for the different regions and cancers, including some overall spatial clustering for specific regions and distances. We did not find statistically significant clusters.

Conclusions

The variations in the estimated empirical D(s) for the different regions and cancers could be partially explained by the differences in the spatial distribution of the population; however, according to the literature, we cannot discard environmental hazards or infections agents in the etiology of these cancers.

Descriptive epidemiology of typhoid fever during an epidemic in Harare, Zimbabwe, 2012

BACKGROUND

Typhoid fever remains a significant public health problem in developing countries. In October 2011, a typhoid fever epidemic was declared in Harare, Zimbabwe - the fourth enteric infection epidemic since 2008. To orient control activities, we described the epidemiology and spatiotemporal clustering of the epidemic in Dzivaresekwa and Kuwadzana, the two most affected suburbs of Harare.

METHODS

A typhoid fever case-patient register was analysed to describe the epidemic. To explore clustering, we constructed a dataset comprising GPS coordinates of case-patient residences and randomly sampled residential locations (spatial controls). The scale and significance of clustering was explored with Ripley K functions. Cluster locations were determined by a random labelling technique and confirmed using Kulldorff's spatial scan statistic.

PRINCIPAL FINDINGS

We analysed data from 2570 confirmed and suspected case-patients, and found significant spatiotemporal clustering of typhoid fever in two non-overlapping areas, which appeared to be linked to environmental sources. Peak relative risk was more than six times greater than in areas lying outside the cluster ranges. Clusters were identified in similar geographical ranges by both random labelling and Kulldorff's spatial scan statistic. The spatial scale at which typhoid fever clustered was highly localised, with significant clustering at distances up to 4.5 km and peak levels at approximately 3.5 km. The epicentre of infection transmission shifted from one cluster to the other during the course of the epidemic.

CONCLUSIONS

This study demonstrated highly localised clustering of typhoid fever during an epidemic in an urban African setting, and highlights the importance of spatiotemporal analysis for making timely decisions about targetting prevention and control activities and reinforcing treatment during epidemics. This approach should be integrated into existing surveillance systems to facilitate early detection of epidemics and identify their spatial range.

Diversity and dynamics of the Vibrio community in well water used for drinking in Guinea-Bissau (West Africa)

Bacteria of the genus Vibrio are ubiquitous in aquatic environments and can be found either in culturable or in a viable but nonculturable (VBNC) state. The genus comprises many pathogenic species accountable for water and food-borne diseases that prove to be fatal, especially in developing countries, as in Guinea-Bissau (West Africa), where cholera is endemic. In order to ascertain the abundance and structure of Vibrio spp. community in well waters that serve as the sole source of water for the population, quantitative polymerase chain reaction (qPCR), PCR-denaturant gradient gel electrophoresis (DGGE), and cloning approaches were used. Results suggest that Vibrio spp. were present throughout the year in acidic, freshwater wells with a seasonal community composition shift. Vibrio spp. abundance was in accordance with the abundance found in coastal environments. Sequences closely related to pathogenic Vibrio species were retrieved from well water revealing exposure of the population to such pathogens. pH, ammonium, and turbidity, regulated by the rain pattern, seem to be the variables that contributed mostly to the shaping and selection of the Vibrio spp. community. These results reinforce the evidence for water monitoring with culture-independent methods and the clear need to create/recover water infrastructures and a proper water resources management in West African countries with similar environmental conditions.

Prevalence of antibiotic resistance in bacteria isolated from drinking well water available in Guinea-Bissau (West Africa)

The dissemination of antibiotic-resistant bacteria and the spread of antibiotic resistance genes are a major public health concern worldwide, being even proposed as emerging contaminants. The aquatic environment is a recognized reservoir of antibiotic resistant bacteria, and antibiotic resistance genes have been recently detected in drinking water. In this study, the water quality and the prevalence of antibiotic resistance of heterotrophic culturable bacteria were characterized seasonally in wells that serve the population of Guinea-Bissau (West Africa) as the sole source of water for drinking and other domestic proposes. The results revealed that well water was unfit for human consumption independently of the season, owing to high acidity and heavy fecal contamination. Moreover, potentially pathogenic bacteria, which showed resistance to the most prescribed antibiotics in Guinea-Bissau, were isolated from well water, posing an additional health risk. Our results suggest that well water not only fosters the transmission of potential pathogenic bacteria, but also represents an important reservoir for the proliferation of antibiotic resistant bacteria, that can aggravate the potential to cause disease in a very vulnerable population that has no other alternative but to consume such water.

Analysis of the bacterial community composition in acidic well water used for drinking in Guinea-Bissau, West Africa

Potable water is a resource out of reach for millions worldwide, and the available water may be chemically and microbiologically compromised. This is particularly acute in Africa, where water-networks may be non-existent or restricted to a small fraction of the urban population, as in the case of Guinea-Bissau, West Africa. This study was carried out seasonally in Bolama (11°N), where unprotected hand-dug wells with acidic water are the sole source of water for the population. We inspected the free-living bacterial community dynamics by automated rRNA intergenic spacer analyses, quantitative polymerase chain reaction and cloning approaches. The results revealed a clear seasonal shift in bacterial assemblage composition and microbial abundance within the same sampling site. Temperature, pH and turbidity, together with the infiltration and percolation of surface water, which takes place in the wet season, seemed to be the driving factors in the shaping and selection of the bacterial community and deterioration of water quality. Analysis of 16S rDNA sequences revealed several potential pathogenic bacteria and uncultured bacteria associated with water and sediments, corroborating the importance of a culture-independent approach in drinking water monitoring.

Evaluation of enrichment method for the detection of Vibrio cholerae O1 using a rapid dipstick test in Bangladesh

BACKGROUND

To evaluate the specificity of the Crystal VC dipstick test for detecting cholera.

METHODS

We compared direct testing using the Crystal VC dipstick test and testing after enrichment for 6 h in alkaline peptone water (APW) to bacterial culture as the gold standard. Samples positive by dipstick but negative by culture were also tested using PCR.

RESULTS

Stool was collected from 125 patients. The overall specificities of the direct testing and testing after 6-h enrichment in APW compared to bacterial culture were 91.8% and 98.4% (P = 0.125), respectively, and the sensitivities were 65.6% and 75.0% (P = 0.07), respectively.

CONCLUSION

The increase in the sensitivity of the Crystal VC kit with the use of the 6-h enrichment step in APW compared to direct testing was marginally significant. The Crystal VC dipstick had a much higher specificity than previously reported (91-98%). Therefore, this method might be a promising screening tool for cholera outbreak surveillance in resource-limited settings where elimination of false-positive results is critical.

Cholera outbreaks in Africa

During the current seventh cholera pandemic, Africa bore the major brunt of global disease burden. More than 40 years after its resurgence in Africa in 1970, cholera remains a grave public health problem, characterized by large disease burden, frequent outbreaks, persistent endemicity, and high CFRs, particularly in the region of the central African Great Lakes which might act as reservoirs for cholera. There, cases occur year round with a rise in incidence during the rainy season. Elsewhere in sub-Saharan Africa, cholera occurs mostly in outbreaks of varying size with a constant threat of widespread epidemics. Between 1970 and 2011, African countries reported 3,221,050 suspected cholera cases to the World Health Organization, representing 46 % of all cases reported globally. Excluding the Haitian epidemic, sub-Saharan Africa accounted for 86 % of reported cases and 99 % of deaths worldwide in 2011. The number of cholera cases is possibly much higher than what is reported to the WHO due to the variation in modalities, completeness, and case definition of national cholera data. One source on country specific incidence rates for Africa, adjusting for underreporting, estimates 1,341,080 cases and 160,930 deaths (52.6 % of 2,548,227 estimated cases and 79.6 % of 209,216 estimated deaths worldwide). Another estimates 1,411,453 cases and 53,632 deaths per year, respectively (50 % of 2,836,669 estimated cases and 58.6 % of 91,490 estimated deaths worldwide). Within Africa, half of all cases between 1970 and 2011 were notified from only seven countries: Angola, Democratic Republic of the Congo, Mozambique, Nigeria, Somalia, Tanzania, and South Africa. In contrast to a global trend of decreasing case fatality ratios (CFRs), CFRs have remained stable in Africa at approximately 2 %. Early propagation of cholera outbreaks depends largely on the extent of individual bacterial shedding, host and organism characteristics, the likelihood of people coming into contact with an infectious dose of Vibrio cholerae and on the virulence of the implicated strain. Cholera transmission can then be amplified by several factors including contamination of human water- or food sources; climate and extreme weather events; political and economic crises; high population density combined with poor quality informal housing and poor hygiene practices; spread beyond a local community through human travel and animals, e.g., water birds. At an individual level, cholera risk may increase with decreasing immunity and hypochlorhydria, such as that induced by Helicobacter pylori infection, which is endemic in much of Africa, and may increase individual susceptibility and cholera incidence. Since contaminated water is the main vehicle for the spread of cholera, the obvious long-term solution to eradicate the disease is the provision of safe water to all African populations. This requires considerable human and financial resources and time. In the short and medium term, vaccination may help to prevent and control the spread of cholera outbreaks. Regardless of the intervention, further understanding of cholera biology and epidemiology is essential to identify populations and areas at increased risk and thus ensure the most efficient use of scarce resources for the prevention and control of cholera.

First outbreak response using an oral cholera vaccine in Africa: vaccine coverage, acceptability and surveillance of adverse events, Guinea, 2012

BACKGROUND

Despite World Health Organization (WHO) prequalification of two safe and effective oral cholera vaccines (OCV), concerns about the acceptability, potential diversion of resources, cost and feasibility of implementing timely campaigns has discouraged their use. In 2012, the Ministry of Health of Guinea, with the support of Médecins Sans Frontières organized the first mass vaccination campaign using a two-dose OCV (Shanchol) as an additional control measure to respond to the on-going nationwide epidemic. Overall, 316,250 vaccines were delivered. Here, we present the results of vaccination coverage, acceptability and surveillance of adverse events.

METHODOLOGY/PRINCIPAL FINDINGS

We performed a cross-sectional cluster survey and implemented adverse event surveillance. The study population included individuals older than 12 months, eligible for vaccination, and residing in the areas targeted for vaccination (Forécariah and Boffa, Guinea). Data sources were household interviews with verification by vaccination card and notifications of adverse events from surveillance at vaccination posts and health centres. In total 5,248 people were included in the survey, 3,993 in Boffa and 1,255 in Forécariah. Overall, 89.4% [95%CI:86.4-91.8%] and 87.7% [95%CI:84.2-90.6%] were vaccinated during the first round and 79.8% [95%CI:75.6-83.4%] and 82.9% [95%CI:76.6-87.7%] during the second round in Boffa and Forécariah respectively. The two dose vaccine coverage (including card and oral reporting) was 75.8% [95%CI: 71.2-75.9%] in Boffa and 75.9% [95%CI: 69.8-80.9%] in Forécariah respectively. Vaccination coverage was higher in children. The main reason for non-vaccination was absence. No severe adverse events were notified.

CONCLUSIONS/SIGNIFICANCE

The well-accepted mass vaccination campaign reached high coverage in a remote area with a mobile population. Although OCV should not be foreseen as the long-term solution for global cholera control, they should be integrated as an additional tool into the response.

Spatio-temporal dynamics of cholera during the first year of the epidemic in Haiti

BACKGROUND

In October 2010, cholera importation in Haiti triggered an epidemic that rapidly proved to be the world's largest epidemic of the seventh cholera pandemic. To establish effective control and elimination policies, strategies rely on the analysis of cholera dynamics. In this report, we describe the spatio-temporal dynamics of cholera and the associated environmental factors.

METHODOLOGY/PRINCIPAL FINDINGS

Cholera-associated morbidity and mortality data were prospectively collected at the commune level according to the World Health Organization standard definition. Attack and mortality rates were estimated and mapped to assess epidemic clusters and trends. The relationships between environmental factors were assessed at the commune level using multivariate analysis. The global attack and mortality rates were 488.9 cases/10,000 inhabitants and 6.24 deaths/10,000 inhabitants, respectively. Attack rates displayed a significantly high level of spatial heterogeneity (varying from 64.7 to 3070.9 per 10,000 inhabitants), thereby suggesting disparate outbreak processes. The epidemic course exhibited two principal outbreaks. The first outbreak (October 16, 2010-January 30, 2011) displayed a centrifugal spread of a damping wave that suddenly emerged from Mirebalais. The second outbreak began at the end of May 2011, concomitant with the onset of the rainy season, and displayed a highly fragmented epidemic pattern. Environmental factors (river and rice fields: p<0.003) played a role in disease dynamics exclusively during the early phases of the epidemic.

CONCLUSION

Our findings demonstrate that the epidemic is still evolving, with a changing transmission pattern as time passes. Such an evolution could have hardly been anticipated, especially in a country struck by cholera for the first time. These results argue for the need for control measures involving intense efforts in rapid and exhaustive case tracking.

Urban cholera transmission hotspots and their implications for reactive vaccination: evidence from Bissau city, Guinea bissau

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 modeling: challenges to quantitative analysis and predicting the impact of interventions

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.

Bacteriostatic anti-Vibrio parahaemolyticus activity of Pseudoalteromonas sp. strains DIT09, DIT44 and DIT46 isolated from Southern Chilean intertidal Perumytilus purpuratus

We characterised the anti-Vibrio parahaemolyticus (anti-V. parahaemolyticus) marine bacteria DIT09, DIT44 and DIT46 isolated from the intertidal mussel Perumytilus purpuratus. The 16S rRNA gene sequences identify a Pseudoalteromonas sp. that form a clade with P. prydzensis and P. mariniglutinosa. The strains produced bacteriostatic anti-V. parahaemolyticus agents during the exponential growth phase, which were also active against V. cholerae and V. anguillarum, but not on other Gram positive and Gram negative bacteria. Bacteriostatic agents could be permeated by analytic ultra-filtration with 3.5 kDa cut-off, partially precipitated with 70 and 90 % ammonium sulphate, but not extracted with ethyl acetate. Reverse-phase HPLC revealed the production of a set of 5-6 active compounds by each strain (elution from 20 to 40 % acetonitrile), with similar but non identical HPLC patterns. Additionally, V. parahaemolyticus was able to progressively overcome the inhibition of antibiotics in trypticase soy agar with Fe(III) 0.5 up to 2 mM, suggesting the involvement of a set of novel siderophore or active molecules targeted at different Fe-siderophore uptake systems. The overall findings suggest that Pseudoalteromonas sp. DIT strains produce a putatively novel class of bacteriostatic and probably amphiphilic anti-Vibrio agents, indicating the need for further studies with chemical purification followed by their structural and functional characterization. Finally, the crude cell-free extracts, as well as the strains incubated at 10(3) and 10(5) c.f.u./mL, did not cause mortality in Artemia franciscana nauplii, suggesting that these bacteria are serious candidates for further probiotic evaluations with shellfish and fish cultures.

Does the effect of vitamin A supplements depend on vaccination status? An observational study from Guinea-Bissau

Objective Vitamin A supplementation (VAS) is estimated to reduce all-cause mortality by 24%. Previous studies indicate that the effect of VAS may vary with vaccination status. The authors evaluated the effect of VAS provided in campaigns on child survival overall and by sex and vaccination status at the time of supplementation. Design Observational cohort study. Setting and participants The study was conducted in the urban study area of the Bandim Health Project in Guinea-Bissau. The authors documented participation or non-participation in two national vitamin A campaigns in December 2007 and July 2008 for children between 6 and 35 months of age. Vaccination status was ascertained by inspection of vaccination cards. All children were followed prospectively. Outcome measures Mortality rates for supplemented and non-supplemented children were compared in Cox models providing mortality rate ratios (MRRs). Results The authors obtained information from 93% of 5567 children in 2007 and 90% of 5799 children in 2008. The VAS coverage was 58% in 2007 and 68% in 2008. Mortality in the supplemented group was 1.5% (44 deaths/2873 person-years) and 1.6% (20 deaths/1260 person-years) in the non-supplemented group (adjusted MRR=0.78 (0.46; 1.34)). The effect was similar in boys and girls. Vaccination cards were seen for 86% in 2007 and 84% in 2008. The effect of VAS in children who had measles vaccine as their last vaccine (2814 children, adjusted MRR=0.34 (0.14; 0.85)) differed from the effect in children who had diphtheria-tetanus-pertussis vaccine as their last vaccine (3680 children, adjusted MRR=1.29 (0.52; 3.22), p=0.04 for interaction). Conclusion The effect of VAS differed by most recent vaccination, being beneficial after measles vaccine but not after diphtheria-tetanus-pertussis vaccine.