Risk areas and neighborhood-level risk factors for Shigella dysenteriae 1 and Shigella flexneri

An in vivo acute toxicity and anti-shigellosis effect of designed formulation on rat

INTRODUCTION

Shigellosis is an intestinal disease and is one of the main causes of morbidity and mortality among children in India. The study aims to analyze the effect of the designed formulation on the hematological parameters in shigellosis-induced rats and assess the in vivo toxicity of this formulation.

METHODS

Male Wistar rats were housed in different groups. Group 1 is normal control; group 2 is diseased control; group 3 and group 4 diseased rats received 250 mg/kg formulation and 20 mg/kg body weight norfloxacin, respectively, orally once a day. Shigellosis was induced by a single intraperitoneal injection of Shigella flexneri, and bacterial load was calculated using the Shigella agar plate. On completion of the study, blood was collected for hematological as well as electrolyte analysis.

RESULTS

The in vivo acute toxicity results indicate that the formulation is safe up to 2000 mg/kg. Furthermore, formulation significantly (p < 0.05) decreases the bacterial load and increases the RBC, WBC, MCHC, platelet, hemoglobin, and electrolytes (Ca⁺⁺, K⁺, and Na⁺) compared to diseased control.

CONCLUSION

The results support the designed formulation's safety and therapeutic effects and support its use as an alternative medicine for treating shigellosis.

Prevalence and Associated Risk Factors of Salmonella, Shigella, and Intestinal Parasites among Food Handlers in Motta Town, North West Ethiopia

Background

Intestinal parasite, Salmonella, and Shigella infections are the main public health concerns in the world, especially in developing countries due to inaccessibility of safe water and unhygienic food handling practices of food handlers.

Methods

A cross-sectional study was conducted in food handlers in Motta town, from February 2019 to April 2019. The study was undertaken to determine the prevalence and associated risk factors of Salmonella, Shigella, and intestinal parasites among 243 food handlers. Sociodemographic and risk factors were collected using pretested structured questionnaire. The stool sample was collected and examined with direct wet mount and concentration techniques. Culture was performed using xylose lysine deoxycholate agar and MacConkey agar and biochemical tests like Klinger iron agar (KIA), lysine iron agar (LIA), Simmons citrate agar, sulphide indole motility test, citrate utilization, and urease production test were conducted to isolate Salmonella species and Shigella species. An antibiotics susceptibility test was performed with Mueller-Hinton agar using the disk diffusion method. Data were entered using statistical package Epi-Data Version 3.1 and analysed with logistic regression using SPSS version 25 and Fisher's exact test. A p value < 0.05 at 95% CI was considered as statistically significant.

Results

The prevalence of intestinal parasite, Salmonella, and Shigella was 27.6%, 2.5%, and 1.6%, respectively, and hookworm was the predominant intestinal parasite detected in the stool. Antimicrobial resistance was observed in ampicillin and tetracycline (100%) in Salmonella species and Shigella species. Risk factors like fingernail status, fruit washing before eating, cleaning utensils, and regular shoe wearing habit were associated with intestinal parasite, whereas fingernail status and wearing kitchen gown during food service were significantly associated with Salmonella and Shigella infections.

Conclusion

The prevalence of intestinal parasitic infections, Salmonella, and Shigella infections in this study indicates the importance of food handlers as probable sources of enteropathogenic infections. Food handlers should have follow-up on the order of food safety rules and keep their personal hygiene. Hotel owners are responsible to control the health status and their created awareness by given food hygiene training for food handlers. Therefore, policy-makers and implementers should focus on the risk factors to reduce the prevalence below the level of public health importance.

Effects of Crinum jagus Water/Ethanol Extract on Shigella flexneri-Induced Diarrhea in Rats

Diarrheal disease, characterized by the release of more than three loose or liquid stools per day, remains one of the leading causes of morbidity and mortality in children below 5 years of age in developing countries. Many drugs used in diarrhea management face contraindication and, with regard to infectious diarrhea, resistance of some bacterial strains; this therefore increases the need of new alternative and more effective drugs. This study aimed to evaluate anti-Shigella flexneri activities of Crinum jagus water/ethanol extract. In vitro activities were assayed by disc diffusion and agar dilution methods and in vivo section on Shigella flexneri-induced diarrhea in rats. This was done by oral administration of 9 X 10⁸ CFU of Shigella flexneri to rats that were treated twice daily with Crinum jagus water/ethanol extract for seven consecutive days. Ciprofloxacin was used as positive control. Daily Shigella flexneri load was evaluated. After one treatment week, animals were then sacrificed and interleukins (IL-2 and INF-γ), immunoglobulins (IgA and IgM), motilin, vasoactive intestinal peptide, and ions (sodium, potassium, calcium, and chloride) levels were determined. Also, blood cell count was realized. Crinum jagus water/ethanol extract dose-dependently inhibited Shigella flexneri growth with inhibition diameter of 18.90 and 25.36 mm, respectively, at 0.39 and 200 mg/mL. Minimum inhibitory concentration (MIC) was 0.10 mg/mL and minimum bactericidal concentration (MBC) was 0.30 mg/mL with MBC/MIC ratio of 3.0. In Shigella flexneri-induced diarrheic rats, Crinum jagus reduced (p<0.01) diarrheal stools emission and Shigella load and lowered IL-2, INF-γ, IgA, IgM, and motilin blood levels, whereas it increased (p<0.01) vasoactive intestinal peptide, sodium, potassium, calcium, and chloride blood levels. In diarrheal rats, Crinum jagus restored the decreasing white blood cells and haemoglobin and restored the damaged colon epithelium, where it reduced the density of mucus-filled goblet cells. These results confirm the use of Crinum jagus in ethnomedicine in diarrhea treatment.

Spatiotemporal Characteristics of Bacillary Dysentery from 2005 to 2017 in Zhejiang Province, China

Background: This study aimed to analyze the epidemiological and spatiotemporal characteristics of bacillary dysentery in Zhejiang Province and to provide the basis for its monitoring, prevention and control. Methods: This study included cases registered in China Information System for Diseases Control and Prevention from 1 January 2005 to 31 December 2017 in Zhejiang. Descriptive methods were employed to investigate the long trend of this disease: gender distribution, high-risk population, seasonality, and circular distribution was explored to detect the peak period; incidence maps were made to show the incidence trend of disease at county level; spatial autocorrelation was explored and the regions with autocorrelation were detected; and spatiotemporal scan was conducted to map out the high-risk regions of disease and how long they lasted. Statistical significance was assumed at p value of <0.05. Results: A total of 105,577 cases of bacillary dysentery were included, the incidence declining sharply from 45.84/100,000 to 3.44/100,000 with an obvious seasonal peak from July to October. Males were more predisposed to the infection than females. Pre-education children had the highest proportion among all occupation categories. Incidence in all age groups were negatively correlated with the year (p < 0.001), and the incidences were negatively correlated with the age groups in 2005–2008 (p = 0.022, 0.025, 0.044, and 0.047, respectively). Local autocorrelation showed that counties in Hangzhou were high-risk regions of bacillary dysentery. The spatiotemporal scan indicated that all clusters occurred before 2011, and the most likely cluster for disease was found in Hangzhou, Jiaxing and Huzhou. Conclusions: The incidence of bacillary dysentery in Zhejiang from 2005 to 2017 featured spatiotemporal clustering, and remained high in some areas and among the young population. Findings in this study serve as a panorama of bacillary dysentery in Zhejiang and provide useful information for better interventions and public health planning.

Prevalence and characterisation of third-generation cephalosporin-resistant Shigella flexneri isolates from Jiangsu Province, China, 2013-2015

OBJECTIVES

The aim of this study was to assess the prevalence of Shigella flexneri resistance to third-generation cephalosporins (3GCs) and to characterise the underlying resistance mechanisms.

METHODS

A total of 282 S. flexneri strains isolated in 2013-2015 in Jiangsu Province, China, were identified, serotyped and analysed for their susceptibility to 3GCs. The bla_TEM, bla_SHV, bla_OXA-1-like and bla_CTX-M-type extended-spectrum β-lactamase (ESBL) genes were amplified and sequenced by PCR.

RESULTS

Of the 282 S. flexneri strains, 97 (34.4%) were resistant to cefotaxime, from which 68 (24.1%) were also resistant to ceftazidime. ESBL genes were detected in 73/97 isolates (75.3%), of which 66/73 (90.4%) showed resistance to 3GCs. Of the 73 ESBL-positive isolates, 32 (43.8%) were positive for CTX-M-1 group (17 for CTX-M-55, 4 for CTX-M-3, 1 for CTX-M-15, 3 for CTX-M-79 and 7 for CTX-M-123), 31 (42.5%) were positive for CTX-M-9 group (29 for CTX-M-14, 1 for CTX-M-24 and 1 for CTX-M-27), 25 (34.2%) were positive for TEM-types (21 for TEM-1 and 4 for TEM-1b) and 1 (1.4%) was positive for SHV-type (SHV-12); none were positive for CTX-M-2 group, CTX-M-8 group and OXA-type.

CONCLUSION

ESBLs play an important role in Shigella resistance to 3GCs. CTX-M-14 and CTX-M-55 appeared to be the dominant ESBLs in 13 cities of Jiangsu Province. Therefore, it is time to regularly monitor resistance of S. flexneri to 3GCs and to take appropriate measures to manage this problem.

Molecular characterization of virulence and antimicrobial resistance profile of Shigella species isolated from children with moderate to severe diarrhea in northeastern Brazil

Molecular characterization of virulence and antimicrobial resistance profiles were determined for Shigella species isolated from children with diarrhea in Fortaleza, Brazil. Fecal specimens were collected along with socioeconomic and clinical data from children with moderate to severe diarrhea requiring emergency care. Shigella spp. were isolated by standard microbiological techniques, and we developed 4 multiplex polymerase chain reaction assays to detect 16 virulence-related genes (VRGs). Antimicrobial susceptibility tests were performed using disk diffusion assays. S. flexneri and S. sonnei were the predominant serogroups. S. flexneri was associated with low monthly incomes; more severe disease; higher number of VRGs; and presence of pic, set, and sepA genes. The SepA gene was associated with more intense abdominal pain. S. flexneri was correlated with resistance to ampicillin and chloramphenicol, whereas S. sonnei was associated with resistance to azithromycin. Strains harboring higher numbers of VRGs were associated with resistance to more antimicrobials. We highlight the correlation between presence of S. flexneri and sepA, and increased virulence and suggest a link to socioeconomic change in northeastern Brazil. Additionally, antimicrobial resistance was associated with serogroup specificity in Shigella spp. and increased bacterial VRGs.

Environmental Drivers and Predicted Risk of Bacillary Dysentery in Southwest China

Bacillary dysentery has long been a considerable health problem in southwest China, however, the quantitative relationship between anthropogenic and physical environmental factors and the disease is not fully understand. It is also not clear where exactly the bacillary dysentery risk is potentially high. Based on the result of hotspot analysis, we generated training samples to build a spatial distribution model. Univariate analyses, autocorrelation and multi-collinearity examinations and stepwise selection were then applied to screen the potential causative factors. Multiple logistic regressions were finally applied to quantify the effects of key factors. A bootstrapping strategy was adopted while fitting models. The model was evaluated by area under the receiver operating characteristic curve (AUC), Kappa and independent validation samples. Hotspot counties were mainly mountainous lands in southwest China. Higher risk of bacillary dysentery was found associated with underdeveloped socio-economy, proximity to farmland or water bodies, higher environmental temperature, medium relative humidity and the distribution of the Tibeto-Burman ethnicity. A predictive risk map with high accuracy (88.19%) was generated. The high-risk areas are mainly located in the mountainous lands where the Tibeto-Burman people live, especially in the basins, river valleys or other flat places in the mountains with relatively lower elevation and a warmer climate. In the high-risk areas predicted by this study, improving the economic development, investment in health care and the construction of infrastructures for safe water supply, waste treatment and sewage disposal, and improving health related education could reduce the disease risk.

Intracellular and membrane-damaging activities of methyl gallate isolated from Terminalia chebula against multidrug-resistant Shigella spp

Shigella spp. (Shigella dysenteriae, Shigella flexneri, Shigella boydii and Shigella sonnei) cause bacillary dysentery (shigellosis), which is characterized by bloody mucous diarrhoea. Although a variety of antibiotics have been effective for treatment of shigellosis, options are becoming limited due to globally emerging drug resistance. In the present study, in vitro antibacterial activity of methyl gallate (MG) isolated from Terminalia chebula was determined by performing MIC, minimal bactericidal concentration (MBC) and time-kill kinetic studies. Bacterial membrane-damaging activity of MG was determined by membrane perturbation and transmission electron microscopy (TEM). Cellular drug accumulation, cell infection and assessment of intracellular activities of MG and reference antibiotics were performed using HeLa cell cultures. The bactericidal activity of MG against multidrug-resistant (MDR) Shigella spp. in comparison with other commonly used drugs including fluoroquinolone was demonstrated here. TEM findings in the present study revealed that MG caused the total disintegration of inner and outer membranes, and leakage of the cytoplasmic contents of S. dysenteriae. The level of accumulation of MG and tetracycline in HeLa cells incubated for 24  h was relatively higher than that of ciprofloxacin and nalidixic acid (ratio of intracellular concentration/extracellular concentration of antibiotic for MG and tetracycline>ciprofloxacin and nalidixic acid). The viable number of intracellular S. dysenteriae was decreased in a time-dependent manner in the presence of MG (4 × MBC) and reduced to zero within 20  h. The significant intracellular activities of MG suggested that it could potentially be used as an effective antibacterial agent for the treatment of severe infections caused by MDR Shigella spp.

Species-wide whole genome sequencing reveals historical global spread and recent local persistence in Shigella flexneri

Shigella flexneri is the most common cause of bacterial dysentery in low-income countries. Despite this, S. flexneri remains largely unexplored from a genomic standpoint and is still described using a vocabulary based on serotyping reactions developed over half-a-century ago. Here we combine whole genome sequencing with geographical and temporal data to examine the natural history of the species. Our analysis subdivides S. flexneri into seven phylogenetic groups (PGs); each containing two-or-more serotypes and characterised by distinct virulence gene complement and geographic range. Within the S. flexneri PGs we identify geographically restricted sub-lineages that appear to have persistently colonised regions for many decades to over 100 years. Although we found abundant evidence of antimicrobial resistance (AMR) determinant acquisition, our dataset shows no evidence of subsequent intercontinental spread of antimicrobial resistant strains. The pattern of colonisation and AMR gene acquisition suggest that S. flexneri has a distinct life-cycle involving local persistence.

Cholera and shigellosis: different epidemiology but similar responses to climate variability

Background

Comparative studies of the associations between different infectious diseases and climate variability, such as the El Niño-Southern Oscillation, are lacking. Diarrheal illnesses, particularly cholera and shigellosis, provide an important opportunity to apply a comparative approach. Cholera and shigellosis have significant global mortality and morbidity burden, pronounced differences in transmission pathways and pathogen ecologies, and there is an established climate link with cholera. In particular, the specific ecology of Vibrio cholerae is often invoked to explain the sensitivity of that disease to climate.

Methods and Findings

The extensive surveillance data of the International Center for Diarrheal Disease Research, Bangladesh are used here to revisit the known associations between cholera and climate, and to address their similarity to previously unexplored patterns for shigellosis. Monthly case data for both the city of Dhaka and a rural area known as Matlab are analyzed with respect to their association with El Niño and flooding. Linear correlations are examined between flooding and cumulative cases, as well as for flooding and El Niño. Rank-correlation maps are also computed between disease cases in the post-monsoon epidemic season and sea surface temperatures in the Pacific. Similar climate associations are found for both diseases and both locations. Increased cases follow increased monsoon flooding and increased sea surface temperatures in the preceding winter corresponding to an El Niño event.

Conclusions

The similarity in association patterns suggests a systemic breakdown in population health with changing environmental conditions, in which climate variability acts primarily through increasing the exposure risk of the human population. We discuss these results in the context of the on-going debate on the relative importance of the environmental reservoir vs. secondary transmission, as well as the implications for the use of El Niño as an early indicator of flooding and enteric disease risk.

Ask when--not just whether--it's a risk: How regional context influences local causes of diarrheal disease

Contemporary epidemiology is enriched when it incorporates ecological concepts about systems and dependencies. With regard to diarrheal disease, the causes of which are many and interacting, the dynamics of within- and between-community disease transmission have distinct components but are also linked in important ways. However, few investigators have studied how regional-scale disease dynamics affect local patterns of diarrheal disease transmission. Characterizing this dependence is important for identifying local- and regional-level transmission pathways. We used data from active surveillance of diarrheal disease prevalence gathered from February 2004 through July 2007 in 21 neighboring Ecuadorian villages to estimate how disease prevalence in spatially and temporally proximate villages modulates the influences of village-level risk and protective factors. We found that the impact of local, village-level interventions such as improved latrines and water treatment can be quite different under conditions of high and low regional disease prevalence. In particular, water treatment was effective only when regional disease prevalence was low, suggesting that person-to-person spread, not waterborne spread, is probably responsible for most between-village transmission in this region. Additional regional-scale data could enhance our understanding of how regional-scale transmission affects local-scale dynamics.

Genomic analysis of the emergence of 20th century epidemic dysentery

Background

Shigella dysenteriae type 1 (Sd1) causes recurrent epidemics of dysentery associated with high mortality in many regions of the world. Sd1 infects humans at very low infectious doses (10 CFU), and treatment is complicated by the rapid emergence of antibiotic resistant Sd1 strains. Sd1 is only detected in the context of human infections, and the circumstances under which epidemics emerge and regress remain unknown.

Results

Phylogenomic analyses of 56 isolates collected worldwide over the past 60 years indicate that the Sd1 clone responsible for the recent pandemics emerged at the turn of the 20^th century, and that the two world wars likely played a pivotal role for its dissemination. Several lineages remain ubiquitous and their phylogeny indicates several recent intercontinental transfers. Our comparative genomics analysis reveals that isolates responsible for separate outbreaks, though closely related to one another, have independently accumulated antibiotic resistance genes, suggesting that there is little or no selection to retain these genes in-between outbreaks. The genomes appear to be subjected to genetic drift that affects a number of functions currently used by diagnostic tools to identify Sd1, which could lead to the potential failure of such tools.

Conclusions

Taken together, the Sd1 population structure and pattern of evolution suggest a recent emergence and a possible human carrier state that could play an important role in the epidemic pattern of infections of this human-specific pathogen. This analysis highlights the important role of whole-genome sequencing in studying pathogens for which epidemiological or laboratory investigations are particularly challenging.

Electronic supplementary material

The online version of this article (doi: 10.1186/1471-2164-15-355) contains supplementary material, which is available to authorized users.

Microbiological evaluation of water during the 2011 flood crisis in Thailand

In 2011, a severe flood occurred in Thailand, covering nearly half the country in water for several months. The contamination of floodwater and subsequent contamination of water for human consumption could have potentially led to a widespread health crisis. However, to date, no study has been conducted to determine the safety of the waters used for human consumption in Thailand during the severe flood. Therefore, we conducted microbiological analysis of 4 kinds of water (floodwater, river water, tap water, and filtered tap water) collected from industrial and residential areas that were damaged due to flooding. Higher net levels of bacteria were found in water with a higher turbidity. No clear trend was observed in the pH value of all 4 water samples. The level of total bacterial contamination in the water samples was estimated by real-time quantitative polymerase chain reaction (PCR). Eleven of the 12 tap water samples and all of the filtered tap water samples had a total bacterial load that exceeded the Thai water quality standards. One of the tap water samples and one of the filtered tap water samples were found to be positive for Shigella sp., although none of the floodwater samples showed detectable levels of this pathogen as determined by PCR analysis. One of the samples of floodwater was also found to be positive for Leptospira sp., but none of the tap water or filtered tap water samples were positive. Most of the tap water samples and all filtered tap water samples were found to be contaminated with Vibrio cholerae. Bacterial contamination in water samples was also analyzed by denaturing gradient gel electrophoresis (DGGE) analysis. These results revealed that several microorganisms were transferred via floodwater to different areas in the central part of Thailand and cross-contaminated between floodwater and water for human consumption.

Integration of Spatial and Social Network Analysis in Disease Transmission Studies

This study presents a case study of how social network and spatial analytical methods can be used simultaneously for disease transmission modeling. The paper first reviews strategies employed in previous studies and then offers the example of transmission of two bacterial diarrheal diseases in rural Bangladesh. The goal is to understand how diseases vary socially above and beyond the effects of the local neighborhood context. Patterns of cholera and shigellosis incidence are analyzed in space and within kinship-based social networks in Matlab, Bangladesh. Data include a spatially referenced longitudinal demographic database which consists of approximately 200,000 people and laboratory-confirmed cholera and shigellosis 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. Combined spatial effects-spatial disturbance models are built to simultaneously analyze spatial and social effects while controlling for local environmental context. Results indicate that cholera and shigellosis always clusters in space and only sometimes within social networks. This suggests that the local environment is most important for understanding transmission of both diseases however kinship-based social networks also influence their transmission. Simultaneous spatial and social network analysis can help us better understand disease transmission and this study has offered several strategies on how.

Impact of population and latrines on fecal contamination of ponds in rural Bangladesh

A majority of households in Bangladesh rely on pond water for hygiene. Exposure to pond water fecal contamination could therefore still contribute to diarrheal disease despite the installation of numerous tubewells for drinking. The objectives of this study are to determine the predominant sources (human or livestock) of fecal pollution in ponds and examine the association between local population, latrine density, latrine quality and concentrations of fecal bacteria and pathogens in pond water. Forty-three ponds were analyzed for E. coli using culture-based methods and E. coli, Bacteroidales and adenovirus using quantitative PCR. Population and sanitation spatial data were collected and measured against pond fecal contamination. Humans were the dominant source of fecal contamination in 79% of the ponds according to Bacteroidales measurements. Ponds directly receiving latrine effluent had the highest concentrations of fecal indicator bacteria (up to 10⁶ Most Probable Number (MPN) of culturable E. coli per 100 mL). Concentrations of fecal indicator bacteria correlated with population surveyed within a distance of 30-70 m (p<0.05) and total latrines surveyed within 50-70 m (p<0.05). Unsanitary latrines (visible effluent or open pits) within the pond drainage basin were also significantly correlated to fecal indicator concentrations (p<0.05). Water in the vast majority of the surveyed ponds contained unsafe levels of fecal contamination attributable primarily to unsanitary latrines, and to lesser extent, to sanitary latrines and cattle. Since the majority of fecal pollution is derived from human waste, continued use of pond water could help explain the persistence of diarrheal disease in rural South Asia.

Diarrheal disease risk in rural Bangladesh decreases as tubewell density increases: a zero-inflated and geographically weighted analysis

BACKGROUND

This study investigates the impact of tubewell user density on cholera and shigellosis events in Matlab, Bangladesh between 2002 and 2004. Household-level demographic, health, and water infrastructure data were incorporated into a local geographic information systems (GIS) database. Geographically-weighted regression (GWR) models were constructed to identify spatial variation of relationships across the study area. Zero-inflated negative binomial regression models were run to simultaneously measure the likelihood of increased magnitude of disease events and the likelihood of zero cholera or shigellosis events. The aim of this study was to examine the effect of tubewell density on both the occurrence of diarrheal disease and the magnitude of diarrheal disease incidence.

RESULTS

In Matlab, households with greater tubewell density were more likely to report zero cholera or shigellosis events. Results for both cholera and shigellosis GWR models suggest that tubewell density effects are spatially stationary and the use of non-spatial statistical methods is appropriate.

CONCLUSIONS

Increasing the amount of drinking water available to households through increased density of tubewells contributed to lower reports of cholera and shigellosis events in rural Bangladesh. Our findings demonstrate the importance of tubewell installation and access to groundwater in reducing diarrheal disease events in the developing world.

Water microbiology. Bacterial pathogens and water

Water is essential to life, but many people do not have access to clean and safe drinking water and many die of waterborne bacterial infections. In this review a general characterization of the most important bacterial diseases transmitted through water—cholera, typhoid fever and bacillary dysentery—is presented, focusing on the biology and ecology of the causal agents and on the diseases’ characteristics and their life cycles in the environment. The importance of pathogenic Escherichia coli strains and emerging pathogens in drinking water-transmitted diseases is also briefly discussed. Microbiological water analysis is mainly based on the concept of fecal indicator bacteria. The main bacteria present in human and animal feces (focusing on their behavior in their hosts and in the environment) and the most important fecal indicator bacteria are presented and discussed (focusing on the advantages and limitations of their use as markers). Important sources of bacterial fecal pollution of environmental waters are also briefly indicated. In the last topic it is discussed which indicators of fecal pollution should be used in current drinking water microbiological analysis. It was concluded that safe drinking water for all is one of the major challenges of the 21st century and that microbiological control of drinking water should be the norm everywhere. Routine basic microbiological analysis of drinking water should be carried out by assaying the presence of Escherichia coli by culture methods. Whenever financial resources are available, fecal coliform determinations should be complemented with the quantification of enterococci. More studies are needed in order to check if ammonia is reliable for a preliminary screening for emergency fecal pollution outbreaks. Financial resources should be devoted to a better understanding of the ecology and behavior of human and animal fecal bacteria in environmental waters.

Spatio-temporal clustering of cholera: the impact of flood control in Matlab, Bangladesh, 1983-2003

Introducing flood control to an area of endemic waterborne diseases could have significant impacts on spatio-temporal occurrence of cholera. Using 21-year data from Bangladesh, we conducted cluster analysis to explore changes in spatial and temporal distribution of cholera incidence since the construction of flood control structures. Striking changes in temporal cluster patterns emerged, including a shift from dry-season to rainy-season clusters following flood protection and delayed clustering inside the protected areas. Spatial differences in pre-flood protection and post-protection cholera clusters are weaker. Changes in spatio-temporal cholera clustering, associated with implementation of flood protection strategies, could affect local cholera prevention efforts.