Cholera in Piura, Peru: a modern urban epidemic

Cholera dynamics: lessons from an epidemic

Cholera is a severe diarrhoeal disease that spreads rapidly and affects millions of people each year, resulting in tens of thousands of deaths. The disease is caused by Vibrio cholerae O1 and is characterized by watery diarrhoea that can be lethal if not properly treated. Cholera had not been reported in South America from the late 1800s until 1991, when it was introduced in Peru, wreaking havoc in one of the biggest epidemics reported to date. Within a year, the disease had spread to most of the Latin American region, resulting in millions of cases and thousands of deaths in all affected countries. Despite its aggressive entry, cholera virtually disappeared from the continent after 1999. The progression of the entire epidemic was well documented, making it an ideal model to understand cholera dynamics. In this review, we highlight how the synergy of socioeconomic, political and ecological factors led to the emergence, rapid spread and eventual disappearance of cholera in Latin America. We discuss how measures implemented during the cholera epidemic drastically changed its course and continental dynamics. Finally, we synthesize our findings and highlight potential lessons that can be learned for efficient and standardized cholera management programmes during future outbreaks in non-endemic areas.

Spatial dynamics and the basic reproduction number of the 1991-1997 Cholera epidemic in Peru

After being cholera free for over 100 years, Peru experienced an unprecedented epidemic of Vibrio cholerae O1 that began in 1991 and generated multiple waves of disease over several years. We developed a mechanistic transmission model that accounts for seasonal variation in temperature to estimate spatial variability in the basic reproduction number ([Formula: see text]), the initial concentration of vibrios in the environment, and cholera reporting rates. From 1991-1997, cholera spread following a multi-wave pattern, with weekly incidence concentrated during warm seasons. The epidemic first hit the coastal departments of Peru and subsequently spread through the highlands and jungle regions. The correlation between model predictions and observations was high (range in R2: 58% to 97%). Department-level population size and elevation explained significant variation in spatial-temporal transmission patterns. The overall R0 across departments was estimated at 2.1 (95% CI: 0.8,7.3), high enough for sustained transmission. Geographic-region level [Formula: see text] varied substantially from 2.4 (95% CI: 1.1, 7.3) for the coastal region, 1.9 (0.7, 6.4) for the jungle region, and 1.5 (0.9, 2.2) for the highlands region. At the department level, mean [Formula: see text] ranged from 0.8 to 6.9. Department-level [Formula: see text] were correlated with overall observed attack rates (Spearman ρ = 0.59, P = 0.002), elevation (ρ = -0.4, P = 0.04), and longitude (ρ = -0.6, P = 0.004). We find that both [Formula: see text] and the initial concentration of vibrios were higher in coastal departments than other departments. Reporting rates were low, consistent with a substantial fraction of asymptomatic or mild cases associated with the El Tor cholera biotype. Our results suggest that cholera vibrios, autochthonous to plankton in the natural aquatic environment, may have triggered outbreaks in multiple coastal locations along the Pacific coast of Peru. Our methodology could be useful to investigate multi-wave epidemics of cholera and could be extended to conduct near real-time forecasts and investigate the impact of vaccination strategies.

Diarrhoea, enteric pathogen detection and nutritional indicators among controls in the Global Enteric Multicenter Study, Kenya site: an opportunity to understand reference populations in case-control studies of diarrhoea

Given the challenges in accurately identifying unexposed controls in case–control studies of diarrhoea, we examined diarrhoea incidence, subclinical enteric infections and growth stunting within a reference population in the Global Enteric Multicenter Study, Kenya site. Within ‘control’ children (0–59 months old without diarrhoea in the 7 days before enrolment, n = 2384), we examined surveys at enrolment and 60-day follow-up, stool at enrolment and a 14-day post-enrolment memory aid for diarrhoea incidence. At enrolment, 19% of controls had ⩾1 enteric pathogen associated with moderate-to-severe diarrhoea (‘MSD pathogens’) in stool; following enrolment, many reported diarrhoea (27% in 7 days, 39% in 14 days). Controls with and without reported diarrhoea had similar carriage of MSD pathogens at enrolment; however, controls reporting diarrhoea were more likely to report visiting a health facility for diarrhoea (27% vs. 7%) or fever (23% vs. 16%) at follow-up than controls without diarrhoea. Odds of stunting differed by both MSD and ‘any’ (including non-MSD pathogens) enteric pathogen carriage, but not diarrhoea, suggesting control classification may warrant modification when assessing long-term outcomes. High diarrhoea incidence following enrolment and prevalent carriage of enteric pathogens have implications for sequelae associated with subclinical enteric infections and for design and interpretation of case–control studies examining diarrhoea.

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.

Vibrio spp. infections

Vibrio is a genus of ubiquitous bacteria found in a wide variety of aquatic and marine habitats; of the >100 described Vibrio spp., ~12 cause infections in humans. Vibrio cholerae can cause cholera, a severe diarrhoeal disease that can be quickly fatal if untreated and is typically transmitted via contaminated water and person-to-person contact. Non-cholera Vibrio spp. (for example, Vibrio parahaemolyticus, Vibrio alginolyticus and Vibrio vulnificus) cause vibriosis - infections normally acquired through exposure to sea water or through consumption of raw or undercooked contaminated seafood. Non-cholera bacteria can lead to several clinical manifestations, most commonly mild, self-limiting gastroenteritis, with the exception of V. vulnificus, an opportunistic pathogen with a high mortality that causes wound infections that can rapidly lead to septicaemia. Treatment for Vibrio spp. infection largely depends on the causative pathogen: for example, rehydration therapy for V. cholerae infection and debridement of infected tissues for V. vulnificus-associated wound infections, with antibiotic therapy for severe cholera and systemic infections. Although cholera is preventable and effective oral cholera vaccines are available, outbreaks can be triggered by natural or man-made events that contaminate drinking water or compromise access to safe water and sanitation. The incidence of vibriosis is rising, perhaps owing in part to the spread of Vibrio spp. favoured by climate change and rising sea water temperature.

A Systematic Review and Meta-Analysis of the Association between Water, Sanitation, and Hygiene Exposures and Cholera in Case-Control Studies

Case-control studies are conducted to identify cholera transmission routes. Water, sanitation, and hygiene (WASH) exposures can facilitate cholera transmission (risk factors) or interrupt transmission (protective factors). To our knowledge, the association between WASH exposures and cholera from case-control studies has not been systematically analyzed. A systematic review was completed to close this gap, including describing the theory of risk and protection, developing inclusion criteria, searching and selecting studies, assessing quality of evidence, and summarizing associations between cholera and seven predicted WASH protective factors and eight predicted WASH risk factors using meta-analysis and sensitivity analysis. Overall, 47 articles describing 51 individual studies from 30 countries met the inclusion criteria. All eight predicted risk factors were associated with higher odds of cholera (odds ratio [OR] = 1.9-5.6), with heterogeneity (I²) of 0-92%. Of the predicted protective factors, five of seven were associated with lower odds of cholera (OR = 0.35-1.4), with heterogeneity of 57-91%; exceptions were insignificant associations for improved water source (OR = 1.1, heterogeneity 91%) and improved sanitation (OR = 1.4, heterogeneity 68%). Results were robust; 3/70 (5%) associations changed directionality or significance in sensitivity analysis. Meta-analysis results highlight that predicted risk factors are associated with cholera; however, predicted protective factors are not as consistently protective. This variable protection is attributed to 1) cholera transmission via multiple routes and 2) WASH intervention implementation quality variation. Water, sanitation, and hygiene interventions should address multiple transmission routes and be well implemented, according to international guidance, to ensure that field effectiveness matches theoretical efficacy. In addition, future case-control studies should detail WASH characteristics to contextualize results.

Effects of Boiling Drinking Water on Diarrhea and Pathogen-Specific Infections in Low- and Middle-Income Countries: A Systematic Review and Meta-Analysis

Globally, approximately 2 billion people lack microbiologically safe drinking water. Boiling is the most prevalent household water treatment method, yet evidence of its health impact is limited. To conduct this systematic review, we searched four online databases with no limitations on language or publication date. Studies were eligible if health outcomes were measured for participants who reported consuming boiled and untreated water. We used reported and calculated odds ratios (ORs) and random-effects meta-analysis to estimate pathogen-specific and pooled effects by organism group and nonspecific diarrhea. Heterogeneity and publication bias were assessed using I2, meta-regression, and funnel plots; study quality was also assessed. Of the 1,998 records identified, 27 met inclusion criteria and reported extractable data. We found evidence of a significant protective effect of boiling for Vibrio cholerae infections (OR = 0.31, 95% confidence interval [CI] = 0.13-0.79, N = 4 studies), Blastocystis (OR = 0.35, 95% CI = 0.17-0.69, N = 3), protozoal infections overall (pooled OR = 0.61, 95% CI = 0.43-0.86, N = 11), viral infections overall (pooled OR = 0.83, 95% CI = 0.7-0.98, N = 4), and nonspecific diarrheal outcomes (OR = 0.58, 95% CI = 0.45-0.77, N = 7). We found no evidence of a protective effect for helminthic infections. Although our study was limited by the use of self-reported boiling and non-experimental designs, the evidence suggests that boiling provides measureable health benefits for pathogens whose transmission routes are primarily water based. Consequently, we believe a randomized controlled trial of boiling adherence and health outcomes is needed.

The importance of thinking beyond the water-supply in cholera epidemics: A historical urban case-study

BACKGROUND

Planning interventions to respond to cholera epidemics requires an understanding of the major transmission routes. Interrupting short-cycle (household, foodborne) transmission may require different approaches as compared long-cycle (environmentally-mediated/waterborne) transmission. However, differentiating the relative contribution of short- and long-cycle routes has remained difficult, and most cholera outbreak control efforts focus on interrupting long-cycle transmission. Here we use high-resolution epidemiological and municipal infrastructure data from a cholera outbreak in 1853 Copenhagen to explore the relative contribution of short- and long-cycle transmission routes during a major urban epidemic.

METHODOLOGY/PRINCIPAL FINDINGS

We fit a spatially explicit time-series meta-population model to 6,552 physician-reported cholera cases from Copenhagen in 1853. We estimated the contribution of long-cycle waterborne transmission between neighborhoods using historical municipal water infrastructure data, fitting the force of infection from hydraulic flow, then comparing model performance. We found the epidemic was characterized by considerable transmission heterogeneity. Some neighborhoods acted as localized transmission hotspots, while other neighborhoods were less affected or important in driving the epidemic. We found little evidence to support long-cycle transmission between hydrologically-connected neighborhoods. Collectively, these findings suggest short-cycle transmission was significant.

CONCLUSIONS/SIGNIFICANCE

Spatially targeted cholera interventions, such as reactive vaccination or sanitation/hygiene campaigns in hotspot neighborhoods, would likely have been more effective in this epidemic than control measures aimed at interrupting long-cycle transmission, such as improving municipal water quality. We recommend public health planners consider programs aimed at interrupting short-cycle transmission as essential tools in the cholera control arsenal.

Non-O1/non-O139 Vibrio cholerae septicaemia in a Saudi man: a case report

Background. The non-O1/non-O139 serogroups of Vibrio cholerae occur in diverse natural niches, and usually cause mild and self-limiting gastrointestinal illness. However, they have well-documented potential to cause invasive and extra-intestinal infections among immunocompromised patients. Furthermore, their ability to grow in low-salinity surface water, and the existence of asymptomatic human carriers, suggest novel acquisition routes for this unusual infection, even in people without obvious risk factors.

Case presentation. A 62-year-old man presented with epigastric pain, vomiting and fever. The patient had a history of diabetes and cholecystectomy, although our initial examination did not reveal any significant findings that might indicate V. cholerae infection. However, blood cultures subsequently revealed the presence of V. cholerae, which was positively identified using both conventional and modern non-conventional technologies. The identity of the V. cholerae isolate was confirmed using Vitek MS (matrix–assisted laser desorption ionization-time of flight MS) and the FilmArray system, in addition to its initial identification using the Vitek 2 system. The septicaemia was successfully treated using a 14 day course of ciprofloxacin.

Conclusion. The present case highlights the need to remain highly suspicious of non-O1/non-O139 V. cholerae infections in patients with known risk factors, as well as in healthy individuals with epidemiological exposure and compatible clinical symptoms. Special care should be taken to avoid false-positive results from confirmatory laboratory tests, as the organism can grow in fresh water, and the results should be verified using multiple methods.

A cholera outbreak in Alborz Province, Iran: a matched case-control study

OBJECTIVES

A total of 229 confirmed cholera cases were reported in Alborz Province during an outbreak that lasted from June 2011 to August 2011. This study aimed to identify potential sources of transmission in order to determine suitable interventions in similar outbreaks. In other words, the lessons learned from this retrospective study can be utilized to manage future similar outbreaks.

METHODS

An age-matched and sex-matched case-control study was conducted during the outbreak. For each case, two control subjects were selected from the neighborhood. A case of cholera was defined as a bacteriologically confirmed case with signs and symptoms of cholera. This study was conducted from June 14, 2011 through August 23, 2011. The data were analyzed by calculating odds ratios (ORs) using the logistic regression method.

RESULTS

In this outbreak, 229 confirmed cholera cases were diagnosed. The following risk factors were found to be associated with cholera: consumption of unrefrigerated leftover food (OR, 3.05; 95% confidence interval [CI], 1.72 to 5.41), consumption of vegetables and fruits in the previous three days (OR, 2.75; 95% CI, 1.95 to 3.89), and a history of traveling in the previous five days (OR, 5.31; 95% CI, 2.21 to 9.72).

CONCLUSIONS

Consumption of vegetables and fruits has remained an unresolved risk factor in cholera outbreaks in Iran in recent years. In order to reduce the risk of cholera, sanitary standards for fruits and vegetables should be observed at all points from production to consumption, the population should be educated regarding hygienic food storage during outbreaks, and sanitary standards should be maintained when traveling during cholera outbreaks.

El Niño, Climate, and Cholera Associations in Piura, Peru, 1991-2001: A Wavelet Analysis

In Peru, it was hypothesized that epidemic cholera in 1991 was linked to El Niño, the warm phase of El Niño-Southern Oscillation. While previous studies demonstrated an association in 1997-1998, using cross-sectional data, they did not assess the consistency of this relationship across the decade. Thus, how strong or variable an El Niño-cholera relationship was in Peru or whether El Niño triggered epidemic cholera early in the decade remains unknown. In this study, wavelet and mediation analyses were used to characterize temporal patterns among El Niño, local climate variables (rainfall, river discharge, and air temperature), and cholera incidence in Piura, Peru from 1991 to 2001 and to estimate the mediating effects of local climate on El Niño-cholera relationships. The study hypothesis is that El Niño-related connections with cholera in Piura were transient and interconnected via local climate pathways. Overall, our findings provide evidence that a strong El Niño-cholera link, mediated by local hydrology, existed in the latter part of the 1990s but found no evidence of an El Niño association in the earlier part of the decade, suggesting that El Niño may not have precipitated cholera emergence in Piura. Further examinations of cholera epicenters in Peru are recommended to support these results in Piura. For public health planning, the results may improve existing efforts that utilize El Niño monitoring for preparedness during future climate-related extremes in the region.

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.

Cholera in the United States, 2001-2011: a reflection of patterns of global epidemiology and travel

US cholera surveillance offers insight into global and domestic trends. Between 2001 and 2011, 111 cases were reported to the Centers for Disease Control and Prevention. Cholera was associated with international travel in 90 (81%) patients and was domestically acquired in 20 (18%) patients; for one patient, information was not available. From January 2001 to October 2010, the 42 (47%) travel-associated cases were associated with travel to Asia. In October 2010, a cholera epidemic started in Haiti, soon spreading to the Dominican Republic (Hispaniola). From then to December 2011, 40 (83%) of the 48 travel-associated cases were associated with travel to Hispaniola. Of 20 patients who acquired cholera domestically, 17 (85%) reported seafood consumption; 10 (59%) ate seafood from the US Gulf Coast. In summary, an increase in travel-associated US cholera cases was associated with epidemic cholera in Hispaniola in 2010-2011. Travel to Asia and consumption of Gulf Coast seafood remained important sources of US cholera cases.

Risk factors for cholera transmission in Haiti during inter-peak periods: insights to improve current control strategies from two case-control studies

Two community-based density case-control studies were performed to assess risk factors for cholera transmission during inter-peak periods of the ongoing epidemic in two Haitian urban settings, Gonaives and Carrefour. The strongest associations were: close contact with cholera patients (sharing latrines, visiting cholera patients, helping someone with diarrhoea), eating food from street vendors and washing dishes with untreated water. Protective factors were: drinking chlorinated water, receiving prevention messages via television, church or training sessions, and high household socioeconomic level. These findings suggest that, in addition to contaminated water, factors related to direct and indirect inter-human contact play an important role in cholera transmission during inter-peak periods. In order to reduce cholera transmission in Haiti intensive preventive measures such as hygiene promotion and awareness campaigns should be implemented during inter-peak lulls, when prevention activities are typically scaled back.

Survivability ofVibrio choleraeO1 in Cooked Rice, Coffee, and Tea

This study aimed to investigate the survival ofVibrio choleraeO1 in 3 types of preparation for cooked rice,Oryza sativaL., (plain rice, rice with coconut milk, and rice with ginger); coffee,Coffea canephora, (plain coffee, coffee with sugar, and coffee with sweetened condensed milk); and tea,Camellia sinensis, (plain tea, tea with sugar, and tea with sweetened condensed milk) held at room temperature (27°C). The survival ofV. choleraeO1 was determined by spread plate method on TCBS agar. Initial cultures of 8.00 log CFU/mL were inoculated into each food sample. After 6 h incubation, significant growth was only detected in rice with coconut milk (9.67 log CFU/mL;P<0.05). However, all 3 types of rice preparation showed significant growth ofV. choleraeafter 24 h (P<0.05). For coffee and tea preparations,V. choleraesurvived up to 6 h in tea with condensed milk (4.72 log CFU/mL) but not in similar preparation of coffee. This study showed evidence for the survivability ofV. choleraein rice, coffee, and tea. Thus, holding these food and beverages for an extended period of time at room temperature should be avoided.

Knowledge, attitudes, and practices related to treatment and prevention of cholera, Haiti, 2010

In response to the recent cholera outbreak, a public health response targeted high-risk communities, including resource-poor communities in Port-au-Prince, Haiti. A survey covering knowledge and practices indicated that hygiene messages were received and induced behavior change, specifically related to water treatment practices. Self-reported household water treatment increased from 30.3% to 73.9%.

Overview of the impact of epidemic-assistance investigations of foodborne and other enteric disease outbreaks, 1946-2005

Epidemic-assistance investigations (Epi-Aids) in response to outbreaks of foodborne and other enteric pathogens have identified novel pathogens, clinical syndromes, and sequelae; described new reservoirs and vehicles of transmission; evaluated existing prevention strategies; and identified deficiencies in the food safety systems on local, national, and international levels. Since the first Epi-Aid was issued in 1946, approximately 23% (1,023 of 4,484 for which investigations were initiated) of all Epi-Aids have been related to foodborne or other enteric diseases. Epi-Aid results have yielded valuable insights into the epidemiology of these pathogens and have molded prevention strategies for detecting, responding to, and preventing future outbreaks. New challenges, brought about in part by centralization and globalization of the food supply, will continue to emerge. The need for Epi-Aids of such outbreaks undoubtedly will persist as an integral part of future public health response efforts, prevention strategies, and training programs.

Epidemic cholera in a crowded urban environment, Port-au-Prince, Haiti

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.

Waterborne cholera outbreak following Cyclone Aila in Sundarban area of West Bengal, India, 2009

Following Cyclone Aila, a block of Sundarban area, West Bengal, India, reported an increased number of diarrhoea cases at the end of May 2009. This study was performed to identify the agent and source of the outbreak as well as to propose control measures. The outbreak is described by time, place and person. A matched case-control study was conducted and rectal swabs and water specimens were collected. In total, 1076 probable case patients and 14 deaths (attack rate 44/10 000) were identified. Vibrio cholerae El Tor Ogawa was isolated from two of five probable case patients' stool specimens. The outbreak started in the fourth week of May, with two peaks in the second and fourth weeks of June, and lasted until August 2009. Compared with controls, cases were more likely to drink non-chlorinated piped water [matched odds ratio (MOR)=16, 95% CI 4.9-51; population attributable fraction 58%) and were less likely to drink chlorine-treated water (MOR=0.06, 95% CI 0.02-0.18). Villagers broke the water pipelines near their houses for easy access to water. Piped water specimens and stored drinking water were positive for faecal contamination. Contaminated drinking water was the probable source of the cholera outbreak. Repairing the pipelines, chlorination at household level and educating villagers regarding the danger of breached water pipe connections controlled the outbreak.

A comparison of spatial and social clustering of cholera in Matlab, Bangladesh

Infectious diseases often cluster spatially, but can also cluster socially because they are transmitted within social networks. This study compares spatial and social clustering of cholera in rural Bangladesh. Data include a spatially referenced longitudinal demographic database, which consists of approximately 200,000 people and laboratory-confirmed cholera cases from 1983 to 2003. Matrices are created of kinship ties between households using a complete network design and distance matrices are also created to model spatial relationships. Moran's I statistics are calculated to measure clustering within both social and spatial matrices. The results show that cholera always clusters in space and seldom within social networks. Cholera is transmitted mostly through the local environment rather than through person-to-person contact. Comparing spatial and social network analysis can help improve understanding of disease transmission.

Laboratory study of Vibrio cholerae O1 survival on three types of boiled rice (Oryza sativa L.) held at room temperature

This study examined whether the survival of Vibrio cholerae O1 on contaminated cooked rice was influenced by the type of rice. Vibrios survived unchanged on clumps of glutinous white rice (wet, grains adhered) held at room temperature for 24 h. On nonglutinous white rice (slightly moist, grains separate), 30% viable vibrios remained at 24 h. On nonglutinous brown rice (moist, separate, covered with a mucus-like substance), the number of vibrios increased 2.7-fold at 24 h. Survival rates of vibrios on the surfaces of a row of five cooked rice grains after 2 h of exposure at room temperature were 86, 29, 12, and 4% for glutinous rice, white rice, and the endosperm and pericarp of brown rice, respectively. (Each boiled brown rice grain surface was partly pericarp and partly endosperm, which became exposed by a rupture of the pericarp.) Covering each inoculated grain with a similar cooked rice grain surface increased the corresponding figures to 93, 99, 60, and 94%. Scanning electron microscopy revealed that each type of cooked grain surface possessed a distinct microtopography. For example, the surfaces of glutinous rice grains consisted of separated overlapping strips with many holes, while the pericarps of brown rice were flat interspersed with small pits. In conclusion, each type of boiled rice produced a distinct survival pattern of V. cholerae O1 caused by both the distinct gross features and the fine surface characteristics of the rice. The significance of this finding is that the type of rice consumed can be a factor in cholera transmission by contaminated rice.

Faecal contamination of drinking water sources of Dhaka city during the 2004 flood in Bangladesh and use of disinfectants for water treatment

AIMS

To describe the extent of faecal pollution and point of use water treatment strategy during and after the 2004 flood in Dhaka.

METHODS

A total of 300 water samples were collected from 20 different drinking water sources in Kamalapur, Dhaka city from August 2004 to January 2005. The level of faecal contamination was estimated using measurements of faecal indicator bacteria (total coliforms, faecal coliforms and faecal streptococci) and isolation of Vibrio cholerae was carried out following standard procedures. Total dissolved solids, dissolved oxygen, hardness, chloride and pH were also monitored. The efficacy of four disinfectants including Halotab, Zeoline-200, alum potash and bleaching powder were tested as point of use water treatment agents. The unacceptable level of contamination of total coliforms (TC), faecal coliforms (FC) and faecal streptococci (FS) ranged from 23.8% to 95.2%, 28.6% to 95.2% and 33.3% to 90.0%, respectively. The isolation rates of V. cholerae O1 and O139 were both 0.33%, and non-O1/non-O139 was 7.0%.

CONCLUSION

Water collected during and after floods was contaminated with TC, FC, FS and V. cholerae. Although alum potash, bleaching powder, Halotab and Zeoline-200 were all effective general disinfectants, Halotab and Zeoline-200 were superior to bleaching powder and alum potash against FC.

SIGNIFICANCE AND IMPACT OF THE STUDY

During and after floods, point of use water treatment could reduce waterborne diseases among flood-affected people.

Regulation of virulence in Vibrio cholerae: the ToxR regulon

Vibrio cholerae is a gram-negative bacterium that is the causative agent of cholera. This disease consists of enormous fluid loss through stools, which can be fatal. Cholera epidemics appear in explosive outbreaks that have occurred repeatedly throughout history. The virulence factors toxin coregulated pilus (TCP) and cholera toxin (CT) are essential for colonization of the host and enterotoxicity, respectively. These virulence factors are under the control of ToxT, an AraC/XylS family protein that activates transcription of the genes encoding TCP and CT. ToxT is under the control of a virulence regulatory cascade known as the ToxR regulon, which responds to environmental stimuli to ensure maximal virulence-factor induction within the human intestine. An understanding of this intricate signaling pathway is essential for the development of methods to treat and prevent this devastating disease.

Molecular characterization of recent Vibrio cholerae O1, El Tor, Inaba strains isolated from hospitalized patients in Kolkata, India

OBJECTIVES

To study the phenotypic and genotypic characterization of newly emerged V. cholerae O1, Inaba strains isolated from patients with diarrhoea.

METHODS

Bacterial characterization was made using polymerase chain reaction, ribotyping, PFGE and RFLP.

RESULTS

After its first appearance in July 2004, O1 Inaba became the dominant serotype by March 2005 and totally replaced the former dominant serotype, Ogawa from May 2005. Most of the Inaba isolates belong to a new ribotype RIV. Ogawa and also some Inaba strains isolated during the same period were identified as RIII. Similarly, the majority of the Inaba isolates belong to 'H1' pulsotype and one isolate is type 'H', while the Ogawa isolates were mostly 'H' pulsotype. Presence of CTX prophage was detected in a single site of the chromosome with at least two RS elements.

CONCLUSIONS

There has been a switch of dominant serotype from Ogawa to Inaba in the Kolkata region. This is not necessarily due to emergence of a new clone but does serve as an epidemiological marker. Further analysis at the molecular level will be required to define this trend and to monitor future spread to other regions.

Comparison of methods for recovering Vibrio cholerae O1 from ice

Alkaline peptone water (1% peptone, 1% NaCl, pH 8.5) and Trypticase soy yeast extract broth (TSYB) supplemented with 2.5% NaCl (pH 8.5) or 1% NaCl (pH 7.5) were evaluated as enrichment broths for the isolation of Vibrio cholerae O1 from ice. Thirty samples of sterile and nonsterile mineral water were inoculated with cell suspensions of this bacterium, quickly frozen, and stored for 3 days at--18 degrees C. After thawing, samples were analyzed by a three-tube most-probable-number technique. Incubation in TSYB with 2.5% NaCl (pH 8.5) for 18 h at 37 degrees C yielded the highest recovery of V. cholerae O1 cells (P < 0.05), a result that might be attributable to the nutrients and to the NaCl concentration of the TSYB, both of which would promote V. cholerae O1 growth and prevent the growth of competitive microbiota.

Application of antimicrobial ice for reduction of foodborne pathogens (Escherichia coli O157:H7, Salmonella Typhimurium, Listeria monocytogenes) on the surface of fish

AIMS

The efficacy of antimicrobial ice was evaluated for the reduction of foodborne pathogens on the surface of fish.

METHODS AND RESULTS

Antimicrobial ice containing chlorine dioxide (ClO2) was utilized to control foodborne pathogens in laboratory media and on fish skin. Escherichia coli O157:H7, Salmonella serotype Typhimurium and Listeria monocytogenes strains were treated with antimicrobial ice for 30 min on plates of selective agar and for 120 min on fish skin at room temperature, and then incubated for enumeration. After treatment with 100 ppm ClO2 for 30 min, 5.4, 4.4 and 3.2 log10 reduction was obtained with E. coli O157:H7, Salm. Typhimurium and L. monocytogenes on laboratory media, respectively. When antimicrobial ice (100 ppm ClO2) was applied to fish skin for 120 min, total reduction of E. coli O157:H7, Salm. Typhimurium and L. monocytogenes was 4.8, 2.6 and 3.3 log10, respectively.

CONCLUSION

The initial load of foodborne pathogens was reduced by antimicrobial ice and the lowered microbial level was maintained during treatment.

SIGNIFICANCE AND IMPACT OF THE STUDY

The application of antimicrobial ice is a simple and effective method for the safe preservation of fish.

Ice as a vehicle for diarrheagenic Escherichia coli

In a recent study of the microbiological quality of commercial ice, 50 Escherichia coli isolates belonging to different serotypes were found. The potential hazard from these isolates was examined by testing their adherence patterns in HeLa cells and searching for the presence of DNA sequences related to E. coli virulence properties. Twelve potentially diarrheagenic isolates were found and classified as enteroaggregative E. coli (EAEC) based on their ability to produce aggregative adherence to HeLa cells. The remaining isolates were devoid of the virulence properties searched for. The EAEC isolates belonged to 10 different serotypes, among which O128ab:H35 is often found in diarrheic feces. None of these isolates reacted with a specific EAEC DNA probe or carried any of the known EAEC virulence genes. These data indicate that ice may be an important vehicle for transmission of enteropathogens, especially of the EAEC group.

Cholera

Intestinal infection with Vibrio cholerae results in the loss of large volumes of watery stool, leading to severe and rapidly progressing dehydration and shock. Without adequate and appropriate rehydration therapy, severe cholera kills about half of affected individuals. Cholera toxin, a potent stimulator of adenylate cyclase, causes the intestine to secrete watery fluid rich in sodium, bicarbonate, and potassium, in volumes far exceeding the intestinal absorptive capacity. Cholera has spread from the Indian subcontinent where it is endemic to involve nearly the whole world seven times during the past 185 years. V cholerae serogroup O1, biotype El Tor, has moved from Asia to cause pandemic disease in Africa and South America during the past 35 years. A new serogroup, O139, appeared in south Asia in 1992, has become endemic there, and threatens to start the next pandemic. Research on case management of cholera led to the development of rehydration therapy for dehydrating diarrhoea in general, including the proper use of intravenous and oral rehydration solutions. Appropriate case management has reduced deaths from diarrhoeal disease by an estimated 3 million per year compared with 20 years ago. Vaccination was thought to have no role for cholera, but new oral vaccines are showing great promise.

Use of telemedicine in evading cholera outbreak in Mahakumbh Mela, Prayag, UP, India: an encouraging experience

Telemedicine (TM) services a process in which expert medical advice from afar is provided using electronic signals to transfer the medical data from one site to another. As a pilot project to assess the efficacy of TM in developing countries like India, a telemedicine center was set up at the main hospital of Mahakumbh mela--a grand religious fair, at Prayag, a city in north India. The daily reporting of the in-patient and outpatient cases at the fair revealed a surge of diarrhea cases among the pilgrims at the fair. This information was communicated to the referral center at Sanjay Gandhi Post Graduate Institute of Medical Sciences (SGPGIMS), which, with the help of its microbiology department, conducted microbiological examinations of stool samples and rectal swabs of patients along with various water samples. Vibrio cholerae was isolated in 22.6% (7/31) of the samples. This information was immediately relayed to the Main Hospital at the fair online, and then to the health authorities, who took strict and prompt measures to improve hygiene. Subsequently, the number of diarrhea cases decreased considerably in a matter of a few days, and thus an epidemic disaster was averted, which could have created havoc in such a large gathering.

Single multiplex polymerase chain reaction to detect diverse loci associated with diarrheagenic Escherichia coli

We developed and tested a single multiplex polymerase chain reaction (PCR) that detects enterotoxigenic, enteropathogenic, enteroinvasive, and Shiga-toxin–producing Escherichia coli. This PCR is specific, sensitive, and rapid in detecting target isolates in stool and food. Because of its simplicity, economy, and efficiency, this protocol warrants further evaluation in large, prospective studies of polymicrobial substances.

Single multiplex polymerase chain reaction to detect diverse loci associated with diarrheagenic Escherichia coli

We developed and tested a single multiplex polymerase chain reaction (PCR) that detects enterotoxigenic, enteropathogenic, enteroinvasive, and Shiga toxin-producing Escherichia coli. This PCR is specific, sensitive, and rapid in detecting target isolates in stool and food. Because of its simplicity, economy, and efficiency, this protocol warrants further evaluation in large, prospective studies of polymicrobial substances.

Risk assessment in regulatory policy making for human and veterinary public health

Risk assessment is the method of systematically identifying and assessing factors that influence the probability and consequences of a negative event occurring. One responsibility of veterinary medicine is to protect animal and human health. Food animal production uses antibiotics to enhance production. Regulators evaluate new production technology to ensure animal safety and safe, edible products and to make public policy decisions by assessing risks/benefits. The U.S. Food and Drug Administration, Center for Veterinary Medicine's (CVM's) first risk assessment addressed the potential human health impact of campylobacter effects associated with the use of fluoroquinolines in food-producing animals. CVM used the Monte Carlo method to estimate risk byprobability distributions that reflect the uncertainty and variability in the data used for the assessment. Enterococci faecium is a species more likely to be resistant to antibiotics of last resort. Effective control of multidrug-resistant enterococci will requirea better understanding of the transfer of E. faeciumfrom animals to humans and the interaction between E. faecium, the hospital environment, and humans; prudent antibiotic use; better contact isolation in hospitals; and better surveillance. CVM will model these factors in a second, more complex risk assessment designed to examine the indirect transfer of resistance from animals to humans. Use of risk assessments allows researchers, the industry, regulatory authorities, and educators to make better policy decisions regarding antimicrobial use in food animals and humans and the development of resistance. Today the question of whether the use of antimicrobials for growth enhancement infood animals should or should not be terminated for the benefit of human health remains unresolved.

Role of active efflux in association with target gene mutations in fluoroquinolone resistance in clinical isolates of Vibrio cholerae

Quinolones are among the drugs of choice in the management of cholera caused by Vibrio cholerae. In this study, we demonstrate that, in addition to mutations detected in the target genes gyrA and parC, proton motive force-dependent efflux is involved in quinolone resistance in clinical isolates of V. cholerae.

[Hygienic conditions of hot dogs sold on the streets, Brazil]

The study objective was to identify the circumstances where there was risk of contamination of food (hot dogs) prepared and sold on the streets and to establish a preventive action through the creation of key surveillance sites. Data were collected from 20 vending sites using interviews, questionnaires, observations of food handling and storage, and temperature and pH measurements of both meat and sauce, respectively. In 30% of the studied sites, hygienic conditions were rated as regular to extremely poor. Mashed potatoes, chicken and beef preparations were of high risk. These findings showed inappropriate hygienic practices of food preparation and lack of basic knowledge regarding food handling - a public health problem. Given the scarcity of literature and official data on food sold in the streets of Brazil, further studies are recommended.

Foodborne Illnesses

Foodborne illnesses cause a substantial human and financial burden. Despite sanitary infrastructure improvements, the incidence of foodborne bacterial infections due to non-typhoidal salmonellae (NTS), Campylobacter jejuni, and enterohemorrhagic Escherichia coli (EHEC) has risen over the last two decades. Overall, viruses account for two thirds of all foodborne illness. Most foodborne illnesses are self-limited. Supportive therapy with rehydration and the correction of electrolyte abnormalities is usually sufficient. Antibiotics play a beneficial role in the treatment of patients with certain foodborne diseases, such as listeriosis and typhoid fever, and all patients with tissue invasive or bloodstream infections. Immunocompromised patients should be treated presumptively. Antibiotics are of variable efficacy for the treatment of many infections limited to the gastrointestinal tract, and recommendations differ between pathogens. Antibiotics are generally helpful for shigellosis and cholera, and possibly beneficial for campylobacteriosis. However, antibiotics are potentially harmful in uncomplicated NTS and EHEC gastroenteritis and generally should not be used. Toxin-mediated food poisoning usually does not require specific therapy. The exception is botulism, for which botulinum antitoxin is highly efficacious if used early in the course of illness. Empiric therapy for gastroenteritis is possibly beneficial, though the magnitude of benefit is modest and incurs the risk of inadvertently treating NTS or EHEC. The choice of antibiotic should be based on local resistance patterns and the results of susceptibility testing.

Construction of a Vibrio cholerae vaccine candidate using transposon delivery and FLP recombinase-mediated excision

Recent efforts to develop a vaccine against the diarrheal disease cholera have focused on the use of live attenuated strains of the causative organism, Vibrio cholerae. The Ogawa lipopolysaccharide phenotype is expressed by many epidemic strains, and motility defects reduce the risk of reactive diarrhea in vaccine recipients. We therefore converted a motile Inaba(+) vaccine candidate, Peru-2, to a nonmotile Ogawa(+) phenotype using a mariner-based transposon carrying rfbT, the gene required for expression of the Ogawa phenotype. Analysis of 22 nonmotile Peru-2 mutants showed that two were Ogawa(+), and both of these strains had insertions in the flgE gene. It was possible to convert these strains to antibiotic sensitivity by introducing a recombinase that acts on sites flanking the antibiotic marker on the transposon. The resulting strains are competent for colonization in infant mice and may therefore be suitable as vaccine candidates for use either independently or in a combination with strains of different biotypes and serotypes.

Surveillance of bacterial pathogens associated with acute diarrhea in Lima, Peru

OBJECTIVES

A study was conducted in Lima, Peru, from January to April 1995, to determine the bacterial pathogens associated with acute diarrhea in adults, their susceptibility to common antimicrobials, the risk factors involved in cholera transmission, and the best clinical predictors of cholera.

METHODS

A random sample of adult patients with acute diarrhea was studied. Epidemiologic and clinical data and risk factors to acquire diarrheal diseases were evaluated. Identification of bacteria and susceptibility to antimicrobials were determined.

RESULTS

The study included 336 patients. Vibrio cholerae O1 (52.7%), Shigella spp. (4. 8%), and Salmonella spp (2.7%) were the pathogens most commonly isolated. No resistance to antimicrobials was observed. Patients with cholera had less access to municipal water (P = 0.0018) and were less likely to have homes connected to a sewage system (P = 0. 0003) or to have indoor toilet facilities (P = 0.0001) than those without cholera. Liquid stools (odds ratio [OR] = 16.51; confidence interval [CI] = 13.71-19.02; P = 0.003), severe dehydration (OR = 2. 48; CI = 1.57-3.38; P = 0.0083), generalized cramps (OR = 4.63; CI = 3.10-6.17, P < 0.0001), and washerwoman's hands (OR = 2.45; CI = 1. 55-3.34; P = 0.017) were the best clinical predictors of cholera in this setting.

CONCLUSIONS

Cholera is still prevalent in Lima, and people living in environments with low sanitary conditions are especially at risk. Clinical signs of severe dehydration and liquid stools were the best predictors of cholera.

The microbiological quality of ice used to cool drinks and ready-to-eat food from retail and catering premises in the United Kingdom

A survey of 4,346 samples of ice from retail and catering premises examined 3,528 samples (81%) used to cool drinks and 144 samples (3%) from food displays. For 674 samples (15%), the origin was not recorded. Most samples of ice used to cool drinks or ready-to-eat food on displays did not contain coliforms, Escherichia coli, or enterococci. Of the ice used to cool drinks, 9% contained coliforms, 1% E. coli, and 1% enterococci in excess of 10(2) CFU/100 ml, and 11% had an aerobic plate count at 37 degrees C in excess of 10(3) CFU/ml. The microbiological quality of ice used to cool drinks was poorer when melt water was present in the ice buckets. Ice used in food displays was more contaminated than ice used to cool drinks, with 23% containing coliforms, 5% E. coli, and 8% enterococci at 10(2) CFU/100 ml or more. Twenty-nine percent of samples had an aerobic plate count greater than 10(3) CFU/ml. Ice that had been used to cool shellfish was of a lower microbiological quality than samples used to cool ready-to-eat fish, salads, or dairy produce. Samples of ice produced in commercial production facilities were of higher microbiological quality than samples of ice that were not. The microbiological quality of ice was dependent on the type of use, the type of premises, and the type and place of production. Although most ice samples were of acceptable microbiological quality, evidence from this study suggests that the microbiological quality of ice prepared and used at certain premises in the UK is a cause for concern.

Outbreak of cholera in Ibadan, Nigeria

The changing epidemiology of cholera in Ibadan, Nigeria, has become a public health challenge, and outbreaks of the disease have been occurring with increasing frequency since the first outbreak in modern times in 1970. In this outbreak, 1384 persons were seen, diagnosed and treated for the disease at the cholera unit, Ibadan from January to December 1996. The outbreak lasted for a whole year. No child under one year was seen. The age adjusted case fatality rate was 5.3%. Diarrhoea and vomiting were the most common combination of symptoms present in 97.3% of all cases, followed by diarrhoea, vomiting and dehydration (84.3%). The median number of days spent on admission was only 2 days. Cholera cases were clustered within the densely populated and poorly planned areas of the city. Though significantly more cases were seen during the rainy season than during the dry season (p<0.01), the deaths were not seasonally related (p = 0.67). Contamination of otherwise potable sources of water, late presentation to the cholera treatment unit and low levels of knowledge about diseases need to be addressed in order to effectively control this disease in the community. Progress should also be made towards developing a suitable vaccine for the control of this internationally important public health disease so that the responsibility of its control is not left entirely to individuals and communities, particularly in developing countries.

Cholera in Vietnam: changes in genotypes and emergence of class I integrons containing aminoglycoside resistance gene cassettes in vibrio cholerae O1 strains isolated from 1979 to 1996

The number of cholera cases and the mortality rates reported from different regions of Vietnam varied considerably in the period from 1979 to 1996, with between 2,500 and 6,000 cases reported annually from 1992 to 1995. Annual mortality rates ranged from 2.0 to 9.6% from 1979 to 1983 to less than 1.8% after 1983. Major cholera outbreaks were reported from the High Plateau region for the first time in 1994 and 1995; this is an area with limited access to health services and safe drinking-water supplies. All cases were associated with Vibrio cholerae O1. Using ribotyping, cholera toxin (CT) genotyping, and characterization of antibiotic susceptibility patterns and antibiotic resistance genes by PCR, we show that strains isolated after 1990 were clearly different from strains isolated before 1991. In contrast to strains isolated before 1991, 94% of 104 strains isolated after 1990 showed an identical ribotype R1, were resistant to sulfamethoxazole and streptomycin, and showed a different CT genotype. Furthermore, PCR analysis revealed that sulfamethoxazole-resistant strains harbored class I integrons containing a gene cassette ant(3")-1a encoding resistance to streptomycin and spectinomycin. This is, to our knowledge, the first report of class I integrons in V. cholerae. The development of cholera and the changes in the phenotypic and genotypic properties of V. cholerae O1 shown in the present study highlight the importance of monitoring V. cholerae O1 in Vietnam as in other parts of the world. In particular, the emergence of the new ribotype R1 strain containing class I integrons should be further studied.

Epidemiology, genetics, and ecology of toxigenic Vibrio cholerae

Cholera caused by toxigenic Vibrio cholerae is a major public health problem confronting developing countries, where outbreaks occur in a regular seasonal pattern and are particularly associated with poverty and poor sanitation. The disease is characterized by a devastating watery diarrhea which leads to rapid dehydration, and death occurs in 50 to 70% of untreated patients. Cholera is a waterborne disease, and the importance of water ecology is suggested by the close association of V. cholerae with surface water and the population interacting with the water. Cholera toxin (CT), which is responsible for the profuse diarrhea, is encoded by a lysogenic bacteriophage designated CTXPhi. Although the mechanism by which CT causes diarrhea is known, it is not clear why V. cholerae should infect and elaborate the lethal toxin in the host. Molecular epidemiological surveillance has revealed clonal diversity among toxigenic V. cholerae strains and a continual emergence of new epidemic clones. In view of lysogenic conversion by CTXPhi as a possible mechanism of origination of new toxigenic clones of V. cholerae, it appears that the continual emergence of new toxigenic strains and their selective enrichment during cholera outbreaks constitute an essential component of the natural ecosystem for the evolution of epidemic V. cholerae strains and genetic elements that mediate the transfer of virulence genes. The ecosystem comprising V. cholerae, CTXPhi, the aquatic environment, and the mammalian host offers an understanding of the complex relationship between pathogenesis and the natural selection of a pathogen.