Post-monsoon waterlogging-associated upsurge of cholera cases in and around Kolkata metropolis, 2015

A meta-analysis of the regional extreme rainfall events in the Indian sub-continent during the southwest monsoon period

The present review focuses on extreme rainfall events (EREs) over the Indian subcontinent during the southwest monsoon period. The evolution of ERE studies across India concentrates mainly on the regional characteristics that have influenced these events during the past decade. It evolved slowly by accounting for different indices to represent extremes, understanding causative mechanisms, and improving their forecasting. There are many methods for estimating EREs, each suited to various objectives. Rather than seeking a perfect method, the studies may adopt methodologies based on the purpose and scope. Moreover, EREs impose severe socioeconomic impacts on India, with heavy burdens on communities and resources. Factors such as low-pressure systems, Indian Ocean warming, and circulation shifts contribute to these extremes. Northwest India has seen a significant rise in ERE frequency and intensity in recent decades due to enhanced convective instability and moisture transport by various climate drivers. In contrast, Northeast India shows a decline in EREs driven by synoptic systems. EREs in the Himalayas are more complex and influenced by tropical and extratropical drivers. Regions like Kerala and the northeastern states face frequent ERE-linked flooding, while the Western Ghats show a declining trend. The ERE in the different regions show different dynamics due to their heating structure, moisture availability, and atmospheric instability factors. Thus, regional ERE forecasting is complex, but combining numerical models with machine learning can enhance accuracy and reliability. Future projections indicate a significant increase in regional EREs, but uncertainties persist due to models' biases. The findings underscore the need for improved modeling strategies and targeted policy measures to mitigate the adverse impacts of future EREs. This review offers insights into India's current state and research prospects, highlighting critical areas for further investigation and enhanced forecasting.

Cholera Outbreaks in Low- and Middle-Income Countries in the Last Decade: A Systematic Review and Meta-Analysis

Cholera is linked to penury, making low- and middle-income countries (LMICs) particularly vulnerable to outbreaks. In this systematic review, we analyzed the drivers contributing to these outbreaks, focusing on the epidemiology of cholera in LMICs. This review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and was registered in PROSPERO (ID: CRD42024591613). We searched PubMed, Scopus, Web of Science, and Google Scholar to include studies on cholera outbreaks that occurred in LMICs from 1 January 2014 to 21 September 2024. Studies on outbreaks outside LMICs and focusing on sporadic cases were excluded. The risk of bias among included studies was assessed using a modified Downes et al. appraisal tool. Thematic analysis was used to synthesize the qualitative data, and meta-analyses to estimate the pooled prevalence. From 1662 records, 95 studies met inclusion criteria, primarily documenting outbreaks in Africa (74%) and Asia (26%). Contaminated water was the main route of disease transmission. The pooled fatality prevalence was 1.3% (95% CI: 1.1-1.6), and the detection rate among suspected cases was 57.8% (95% CI: 49.2-66.4). Vibrio cholerae O1 was the dominant serogroup while Ogawa was the dominant serotype. All studies reporting biotypes indicated El Tor. Although the isolates were 100% susceptible to ofloxacin, levofloxacin, norfloxacin, cefuroxime, and doxycycline, they were also fully resistant to amikacin, sulfamethoxazole, trimethoprim, and furazolidone. The persistence of cholera outbreaks in destitute areas with limited access to clean water and sanitation emphasizes the need for socioeconomic improvements, infrastructure development, and ongoing surveillance to support timely responses and achieve long-term prevention.

Identifying clustering of cholera cases using geospatial analysis in Kolkata and surrounding districts: data from patients at tertiary care referral hospitals

Background

Cholera cases have increased globally across the Eastern Mediterranean, Africa, Southeast Asia, and parts of Europe since early 2024. This study aims to identify cholera hotspots and understand the spatial distribution of cholera in Kolkata and surrounding regions, a key cholera reservoir. Additionally, we examine sociodemographic factors and aspects related to water, sanitation, and hygiene (WASH).

Methods

Cholera clusters were detected using kernel density estimation and spatial autocorrelation through Global Moran's-I statistics, with local cluster patterns examined using Local Moran's-I statistics. Cholera cases from August 2021 to December 2023, treated at two tertiary care facilities in Kolkata: Infectious Diseases and Beleghata General Hospital and Dr. B C Roy Post Graduate Institute of Paediatric Sciences Hospital were included. Additionally, through a case-control study, 196 culture-confirmed cholera cases and 764 age/sex-matched neighborhood controls were enrolled, to investigate cholera risk factors.

Findings

Spatial analysis revealed a concentration of 196 cholera cases in Kolkata and its surrounding regions of Howrah, Hooghly, and North and South 24 Parganas. Hotspot analysis showed significant clustering in several Kolkata wards (31, 33, 56, 46, 57, 58, 59, 61, 66, 71, and 107), particularly in the northern, central, and east Kolkata wetlands areas (Global Moran's I statistic = 0.14, p < 0.001). These clusters had proximity between cases, with a median distance of 187.7 m, and 25.5% of cases as close as 73.9 m apart, suggesting localized transmission. Hotspots were identified with an average distance of 1600 m between them. Local Moran's I analysis found dense "high-high" clusters in these areas (p < 0.01), with a mean Moran's I index of 0.3, (range 0.1-4.6). The case-control study revealed that males were more likely to contract cholera, with an adjusted odds ratio of 2.4 (p < 0.01). There was no significant association found between cholera infection and sociodemographic factors or various WASH practices.

Interpretation

The findings emphasize the importance of targeted interventions, especially in identified hotspots, to mitigate cholera transmission. Addressing Socio-economic, and environmental factors especially improvement in WASH practices may further enhance prevention effects.

Funding

The author KK, received funding from the program of the Japan Initiative for Global Research Network on Infectious Diseases, (grant id: JP23wm0125004), from the Ministry of Education, Culture, Sports, Science and Technology in Japan, and Japan Agency for Medical Research and Development.

Outbreak of waterborne acute diarrheal disease in a South District village of Tripura: A public health emergency in the Northeast region of India

Food and waterborne outbreaks are a neglected public health problem in India. However, it is important to identify the source of infection and the causative pathogen to curb the outbreak quickly and minimize mortality and morbidity. A retrospective descriptive study was conducted with a line list of 130 diarrheal cases. Epidemiological investigation and laboratory investigation were done. Data were collected from hospital case report forms as well as interviewed affected cases. A case of acute diarrheal disease was reported among the people in the village with abdominal pain, vomiting, and diarrhea from December 31, 2022 to January 3, 2023. Out of a total of 130 recorded cases, 33 stool samples were collected and were positive for Enteroaggregative Escherichia coli, Shigella flexneri 3a, and Shigella sonnei by cultural and molecular tests. The presumptive fecal pollution indicator assay indicated high coliform counts in the water samples (most probable number [MPN]-05) and the presence of Escherichia coli. The identified pathogens showed susceptibility to gentamicin and meropenem. People who used public drinking water were found to be infected with acute diarrheal disease (ADD). Quick identification of the causative pathogens and their antimicrobial resistance pattern helped correct antibiotic prescriptions and quick recovery of the patients without any deaths. Thus, a timely implementation of food and waterborne outbreak investigation is crucial to saving lives and preventing the spread of infection.

Existence of cholera outbreak, challenges, and way forward on public health interventions to control cholera outbreak in Guraghe Zones, southern Ethiopia, 2023

INTRODUCTION

In Ethiopia, despite major improvements seen in health service delivery system, the country continues to be significantly affected by cholera outbreaks. Cholera remains a significant public health problem among the vulnerable populations living in many resource-limited settings with poor access to safe and clean water and hygiene practices. Recurring cholera outbreaks are an indication of deprived water and sanitation conditions as well as weak health systems, contributing to the transmission and spread of the cholera infection.

OBJECTIVE

To assess the cholera outbreak, its challenges, and the way forward on public health interventions to solve the knowledge and health service delivery gaps related to cholera control in Guraghe Zone, Ethiopia, 2023.

METHODS

Active surveillance of the cholera outbreak was conducted in all kebeles and town administrative of Guraghe zone from 7/8/2023 to 30/10/2023. A total of 224 cholera cases were detected during the active surveillance method. Data obtained from Guraghe zone offices were exported to SPSS version 25 for additional analysis. The case fatality rate, incidence of the cases, and other descriptive variables were presented and described using figures and tables.

RESULT

A total of 224 cholera cases were detected through an active surveillance system. In this study, the case fatality rate of cholera outbreak was 2.6%. To tackle the cholera outbreak, the Guraghe zone health office collaborated with other stakeholders to prepare four cholera treatment centers. The absence of OCV, inaccessible safe water, low latrine coverage, inappropriate utilization of latrines, and absence of cholera laboratory rapid diagnostics test in Guraghe Zone are barriers to tackling the outbreak.

CONCLUSION

Ethiopia National Cholera Plan targeted eradicating cholera by 2030, 222 cholera outbreak occurred in Guraghe Zone, Ethiopia. To minimize and control cholera mortality rate oral cholera vaccinations should be employed in all areas of the region. Sustainable WASH measures should be guaranteed for the use of safe water and good hygiene practices. Early diagnosis and treatment should be initiated appropriately for those who are infected.

Seasonality of cholera in Kolkata and the influence of climate

BACKGROUND

Cholera in Kolkata remains endemic and the Indian city is burdened with a high number of annual cases. Climate change is widely considered to exacerbate cholera, however the precise relationship between climate and cholera is highly heterogeneous in space and considerable variation can be observed even within the Indian subcontinent. To date, relatively few studies have been conducted regarding the influence of climate on cholera in Kolkata.

METHODS

We considered 21 years of confirmed cholera cases from the Infectious Disease Hospital in Kolkata during the period of 1999-2019. We used Generalised Additive Modelling (GAM) to extract the non-linear relationship between cholera and different climatic factors; temperature, rainfall and sea surface temperature (SST). Peak associated lag times were identified using cross-correlation lag analysis.

RESULTS

Our findings revealed a bi-annual pattern of cholera cases with two peaks coinciding with the increase in temperature in summer and the onset of monsoon rains. Variables selected as explanatory variables in the GAM model were temperature and rainfall. Temperature was the only significant factor associated with summer cholera (mean temperature of 30.3 °C associated with RR of 3.8) while rainfall was found to be the main driver of monsoon cholera (550 mm total monthly rainfall associated with RR of 3.38). Lag time analysis revealed that the association between temperature and cholera cases in the summer had a longer peak lag time compared to that between rainfall and cholera during the monsoon. We propose several mechanisms by which these relationships are mediated.

CONCLUSIONS

Kolkata exhibits a dual-peak phenomenon with independent mediating factors. We suggest that the summer peak is due to increased bacterial concentration in urban water bodies, while the monsoon peak is driven by contaminated flood waters. Our results underscore the potential utility of preventative strategies tailored to these seasonal and climatic patterns, including efforts to reduce direct contact with urban water bodies in summer and to protect residents from flood waters during monsoon.

Assessment of the urban waterlogging resilience and identification of its driving factors: A case study of Wuhan City, China

With rapid urbanization and extreme rainstorm events associated with climate change, urban waterlogging has become one of the most frequent and severe disasters globally. In this study, a multi-dimensional and multi-process index system based on the Pressure-State-Response (PSR) framework was developed to measure the level of urban waterlogging resilience (UWR). The spatial distribution of UWR on a block scale was explored based on the entropy weight method with the natural breakpoint method (EWM-NBM) in the central district of Wuhan City, China. In addition, the effects of the runoff control facilities and early warning measures on UWR were also quantified. Further, the Geodetector was used to investigate the main driving factors of UWR and their interactions. Results showed that the constructed index system for UWR based on the PSR framework performed reasonably, and the EWM-NBM was validated to be effective in the integrated assessment. In terms of the validation results, 82.72 % of the recorded waterlogging points belonged to high and very-high risk levels. The spatial heterogeneity of UWR was significant in the study area where the higher-level UWR mainly appears in the areas near the undeveloped suburban and water bodies (lakes and rivers), and the lower-level UWR was concentrated in central urban areas with more impervious surfaces. There was a clear increasing trend in UWR after the implementation of runoff control facilities and early warning measures, but its spatial distribution remained almost invariant. Among all the indexes, the impervious surface percentage had the strongest (69.58 %) explanatory ability for the UWR, and mean annual precipitation (15.51 %), GDP (14.03 %), and population density (11.98 %) also demanded attention. Most driving factors of UWR showed nonlinear interactions. This research could provide a benchmark for urban planning to enhance UWR to mitigate the waterlogging within the main urban area.

Antimicrobial resistance in Vibrio cholerae O1/O139 clinical isolates: a systematic review and meta-analysis

OBJECTIVES

Vibrio cholerae O1/O139 is responsible for cholera epidemics; that remains a huge public health menace across the globe. Furthermore, an increasing resistance rate among V. cholerae strains has been reported around the world. Therefore, the objective of this meta-analysis was to evaluate the weighted pooled resistance (WPR) rates in clinical V. cholerae O1/O139 isolates based on different years, areas, antimicrobial susceptibility testing, and resistance rates.

RESEARCH DESIGN AND METHODS

: We searched the studies in PubMed, Scopus, Embase, and Web of Science (until January 2020). Statistical analyses were conducted using STATA software (ver. 14.0).

RESULTS

: A total of 139 studies investigating 24062 V. cholerae O1/O139 isolates were analyzed. The majority of the studies originated in Asia (n=102). The WPR rates were as follows: azithromycin 1%, erythromycin 36%, ciprofloxacin 3%, cotrimoxazole 79%, doxycycline 7%, tetracycline 20%. There was increased resistance to cotrimoxazole, ciprofloxacin, and tetracycline during the 1980 to 2020 years.

CONCLUSIONS

: Temporal changes in antibiotic resistance rate found in this study demonstrated the critical continuous surveillance of antibiotic resistance. Also, ciprofloxacin, azithromycin, gentamicin, cephalexin, imipenem, ofloxacin, and norfloxacin were found to be the best antibiotics against V. cholera, with the highest and the lowest effectiveness resistance rate.

Cholera Outbreaks in India, 2011–2020: A Systematic Review

Fecal contamination of water sources and open defecation have been linked to cholera outbreaks in India. However, a systematic review on the drivers responsible for these outbreaks has yet to be published. Here, we systematically review the published literature on cholera outbreaks in India between 2011 and 2020. We searched studies in English in three databases (MEDLINE, EMBASE, and Web of Science) and the Integrated Disease Surveillance Program that tracks cholera outbreaks throughout India. Two authors independently extracted data and assessed the quality of the included studies. Quantitative data on the modes of transmission reviewed in this study were assessed for any change over time between 2011–2015 and 2016–2020. Our search retrieved 10823 records initially, out of which 81 full-text studies were assessed for eligibility. Among these 81 studies, 20 were eligible for inclusion in this review. There were 565 reported outbreaks between 2011 and 2020 that led to 45,759 cases and 263 deaths. Outbreaks occurred throughout the year; however, they exploded with monsoons (June through September). In Tamil Nadu, a typical peak of cholera outbreaks was observed from December to January. Seventy-two percent (33,089/45,759) of outbreak-related cases were reported in five states, namely Maharashtra, West Bengal, Punjab, Karnataka, and Madhya Pradesh. Analysis of these outbreaks highlighted the main drivers of cholera including contaminated drinking water and food, inadequate sanitation and hygiene (including open defecation), and direct contact between households. The comparison between 2011–2015 and 2016–2020 showed a decreasing trend in the outbreaks that arose due to damaged water pipelines. Many Indians still struggle with open defecation, sanitation, and clean water access. These issues should be addressed critically. In addition, it is essential to interrupt cholera short-cycle transmission (mediated by households, stored drinking water and foodstuffs) during an outbreak. As cholera is associated with deprivation, socio-economic development is the only long-term solution.

Cholera Outbreak in Hadhramout, Yemen: The Epidemiological Weeks 2019

Background and aims: Cholera is a disease of acute watery diarrhea caused by Vibrio cholerae usually transmitted through contaminated water. In this study, we collected and analyzed the related epidemiological data to determine cholera outbreak in Hadhramout, Yemen during the disease epidemic in 2019. Methods: A cross-sectional study was conducted according to screening rapid diagnostic and confirmatory laboratory culture testing methods for diagnosing clinically cholera cases. Results: Suspected cholera cases were tested by rapid diagnostic test (RDT) and 399 (50.5%) out of 794 cases were determined positive, and 76(9.6%) of them were confirmed by laboratory culture test (LCT) with statistically significant difference. Serotype V. cholerae O1 was also detected in patients’ diarrhea. Females were the most affected by the disease manifested in 201 (25.3%) and 43 (5.4%) when tested by RDT and LCT, respectively, with no statistically significant difference. The highest proportion of cholera cases (224) were reported in the age group less than 15 years (56.1%) with statistically significant difference when tested by RDT, and 45(13.3%) when tested by LCT with insignificant statistics difference. Hajr directorate was revealed to be the most affected with 242 (30.47%) followed by Mukalla city directorate with 108 (13.60%) when the cases were tested by RDT; while Hajr and Mukalla city directorates reported 55 (7.0%) and 15 (2.0%), respectively, when it was confirmed by LCT with a statistically significant difference. Conclusion: Severe cholera outbreak occurred during the epidemiological weeks in 2019 in Hadhramout coast. V. cholerae O1 serotype was the causative agent of cholera. Females and age group less than 15 years were the most affected by the disease. Hajr and Mukalla city directorates reported serious outbreak cholera cases.

Cholera Risk: A Machine Learning Approach Applied to Essential Climate Variables

Oceanic and coastal ecosystems have undergone complex environmental changes in recent years, amid a context of climate change. These changes are also reflected in the dynamics of water-borne diseases as some of the causative agents of these illnesses are ubiquitous in the aquatic environment and their survival rates are impacted by changes in climatic conditions. Previous studies have established strong relationships between essential climate variables and the coastal distribution and seasonal dynamics of the bacteria Vibrio cholerae, pathogenic types of which are responsible for human cholera disease. In this study we provide a novel exploration of the potential of a machine learning approach to forecast environmental cholera risk in coastal India, home to more than 200 million inhabitants, utilising atmospheric, terrestrial and oceanic satellite-derived essential climate variables. A Random Forest classifier model is developed, trained and tested on a cholera outbreak dataset over the period 2010–2018 for districts along coastal India. The random forest classifier model has an Accuracy of 0.99, an F1 Score of 0.942 and a Sensitivity score of 0.895, meaning that 89.5% of outbreaks are correctly identified. Spatio-temporal patterns emerged in terms of the model’s performance based on seasons and coastal locations. Further analysis of the specific contribution of each Essential Climate Variable to the model outputs shows that chlorophyll-a concentration, sea surface salinity and land surface temperature are the strongest predictors of the cholera outbreaks in the dataset used. The study reveals promising potential of the use of random forest classifiers and remotely-sensed essential climate variables for the development of environmental cholera-risk applications. Further exploration of the present random forest model and associated essential climate variables is encouraged on cholera surveillance datasets in other coastal areas affected by the disease to determine the model’s transferability potential and applicative value for cholera forecasting systems.

Understanding the Impact of Rainfall on Diarrhea: Testing the Concentration-Dilution Hypothesis Using a Systematic Review and Meta-Analysis

BACKGROUND

Projected increases in extreme weather may change relationships between rain-related climate exposures and diarrheal disease. Whether rainfall increases or decreases diarrhea rates is unclear based on prior literature. The concentration-dilution hypothesis suggests that these conflicting results are explained by the background level of rain: Rainfall following dry periods can flush pathogens into surface water, increasing diarrhea incidence, whereas rainfall following wet periods can dilute pathogen concentrations in surface water, thereby decreasing diarrhea incidence.

OBJECTIVES

In this analysis, we explored the extent to which the concentration-dilution hypothesis is supported by published literature.

METHODS

To this end, we conducted a systematic search for articles assessing the relationship between rain, extreme rain, flood, drought, and season (rainy vs. dry) and diarrheal illness.

RESULTS

A total of 111 articles met our inclusion criteria. Overall, the literature largely supports the concentration-dilution hypothesis. In particular, extreme rain was associated with increased diarrhea when it followed a dry period [incidence rate ratio ( IRR ) = 1.26 ; 95% confidence interval (CI): 1.05, 1.51], with a tendency toward an inverse association for extreme rain following wet periods, albeit nonsignificant, with one of four relevant studies showing a significant inverse association (IRR = 0.911 ; 95% CI: 0.771, 1.08). Incidences of bacterial and parasitic diarrhea were more common during rainy seasons, providing pathogen-specific support for a concentration mechanism, but rotavirus diarrhea showed the opposite association. Information on timing of cases within the rainy season (e.g., early vs. late) was lacking, limiting further analysis. We did not find a linear association between nonextreme rain exposures and diarrheal disease, but several studies found a nonlinear association with low and high rain both being associated with diarrhea.

DISCUSSION

Our meta-analysis suggests that the effect of rainfall depends on the antecedent conditions. Future studies should use standard, clearly defined exposure variables to strengthen understanding of the relationship between rainfall and diarrheal illness. https://doi.org/10.1289/EHP6181.