Associations between open drain flooding and pediatric enteric infections in the MAL-ED cohort in a low-income, urban neighborhood in Vellore, India

Rainfall and Temperature Influences on Childhood Diarrhea and the Effect Modification Role of Water and Sanitation Conditions: A Systematic Review and Meta-Analysis

The latest report from the Intergovernmental Panel on Climate Change (IPCC) highlighted the worsening impacts of climate change. Two climate factors-temperature and rainfall uncertainties-influence the risk of childhood diarrhea, which remains a significant cause of morbidity and mortality in low- and middle-income countries. They create a conducive environment for diarrhea-causing pathogens and overwhelm environmental prevention measures. This study aimed to produce comprehensive evidence on the association of temperature and rainfall variability with the risk of childhood diarrhea and the influence of water and sanitation conditions on those associations. We conducted a systematic review and meta-analysis using the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) approach. Records published in English from 2006 to 2023 were searched on 8 January 2024 via PubMed, EMBASE, ScienceDirect, Scopus, the Cochrane Library, and Google/Google Scholar using comprehensive search terms. We assessed studies for any risk of bias using the Navigation Guide and rated the quality of the evidence using the GRADE approach. The heterogeneity among estimates was assessed using I-squared statistics (I2). The findings of the analysis were presented with forest plots using an incidence rate ratio (IRR). A meta-analysis was conducted on effect modifiers (water supply and sanitation conditions) using a random effects model with a 95% confidence interval (CI). The statistical analyses were conducted using R 4.3.2 software and Review Manager 5.3. A total of 2017 records were identified through searches, and only the 36 articles that met the inclusion criteria were included. The analysis suggests a small positive association between increased temperature and the occurrence of under-five diarrhea, with the pooled IRR = 1.04; 95% CI [1.03, 1.05], at I2 = 56% and p-value < 0.01, and increased rainfall and U5 diarrhea, with IRR = 1.14; 95% CI [1.03, 1.27], at I2 = 86% and p-value < 0.01. The meta-analysis indicated a positive association between unimproved latrine facilities and drinking water sources with a rainfall-modified effect on U5 diarrhea, with IRR = 1.21; 95% CI [0.95, 1.53], at I2 = 62% and p-value = 0.03. We found that an increase in mean temperature and rainfall was associated with an increased risk of childhood diarrhea. Where there were unimproved latrine facilities and drinking water sources, the increase in mean rainfall or temperature would increase the incidence of childhood diarrhea. The results of this review help in assessing the effectiveness of current intervention programs, making changes as needed, or creating new initiatives to lower the prevalence of childhood diarrhea.

A pilot study using hospital surveillance and a birth cohort to investigate enteric pathogens and malnutrition in children, Dili, Timor-Leste

In low-to-middle-income countries (LMICs), enteric pathogens contribute to child malnutrition, affecting nutrient absorption, inducing inflammation, and causing diarrhoea. This is a substantial problem in LMICs due to high disease burden, poor sanitation and nutritional status, and the cyclical nature of pathogen infection and malnutrition. This relationship remains understudied in Timor-Leste. In our pilot study of enteric pathogens and malnutrition in Dili, Timor-Leste (July 2019-October 2020), we recruited 60 infants in a birth cohort from Hospital Nacional Guido Valadares (HNGV) with up to four home visits. We collected faecal samples and details of demographics, anthropometrics, diet and food practices, and animal husbandry. Additionally, we collected faecal samples, diagnostics, and anthropometrics from 160 children admitted to HNGV with a clinical diagnosis of severe diarrhoea or severe acute malnutrition (SAM). We tested faeces using the BioFire® FilmArray® Gastrointestinal Panel. We detected high prevalence of enteric pathogens in 68.8% (95%CI 60.4-76.2%) of infants at home, 88.6% of SAM cases (95%CI 81.7-93.3%) and 93.8% of severe diarrhoea cases (95%CI 67.7-99.7%). Diarrhoeagenic Escherichia coli and Campylobacter spp. were most frequently detected. Pathogen presence did not significantly differ in birth cohort diarrhoeal stool, but hospital data indicated associations between Salmonella and Shigella and diarrhoea. We observed wasting in 18.4% (95%CI 9.2-32.5%) to 30.8% (95%CI 17.5-47.7%) of infants across home visits, 57.9% (95%CI 34.0-78.9%) of severe diarrhoea cases, and 92.5% (95%CI 86.4-96.2%) of SAM cases. We associated bottle feeding with increased odds of pathogen detection when compared with exclusive breastfeeding at home (OR 8.3, 95%CI 1.1-62.7). We detected high prevalence of enteric pathogens and signs of malnutrition in children in Dili. Our pilot is proof of concept for a study to fully explore the risk factors and associations between enteric pathogens and malnutrition in Timor-Leste.

Effects of hydrometeorological and other factors on SARS-CoV-2 reproduction number in three contiguous countries of tropical Andean South America: a spatiotemporally disaggregated time series analysis

Background

The COVID-19 pandemic has caused societal disruption globally, and South America has been hit harder than other lower-income regions. This study modeled the effects of six weather variables on district-level SARS-CoV-2 reproduction numbers (Rt ) in three contiguous countries of tropical Andean South America (Colombia, Ecuador, and Peru), adjusting for environmental, policy, healthcare infrastructural and other factors.

Methods

Daily time-series data on SARS-CoV-2 infections were sourced from the health authorities of the three countries at the smallest available administrative level. Rt values were calculated and merged by date and unit ID with variables from a unified COVID-19 dataset and other publicly available sources for May-December, 2020. Generalized additive models were fitted.

Findings

Relative humidity and solar radiation were inversely associated with SARS-CoV-2 Rt . Days with radiation above 1000 kJ/m2 saw a 1.3% reduction in Rt , and those with humidity above 50% recorded a 0.9% reduction in Rt . Transmission was highest in densely populated districts, and lowest in districts with poor healthcare access and on days with lowest population mobility. Wind speed, temperature, region, aggregate government policy response, and population age structure had little impact. The fully adjusted model explained 4.3% of Rt variance.

Interpretation

Dry atmospheric conditions of low humidity increase district-level SARS-CoV-2 reproduction numbers, while higher levels of solar radiation decrease district-level SARS-CoV-2 reproduction numbers - effects that are comparable in magnitude to population factors like lockdown compliance. Weather monitoring could be incorporated into disease surveillance and early warning systems in conjunction with more established risk indicators and surveillance measures.

Funding

NASA's Group on Earth Observations Work Programme (16-GEO16-0047).

Persistent Ascaris Transmission Is Possible in Urban Areas Even Where Sanitation Coverage Is High

In low-income, urban, informal communities lacking sewerage and solid waste services, onsite sanitation (sludges, aqueous effluent) and child feces are potential sources of human fecal contamination in living environments. Working in informal communities of urban Maputo, Mozambique, we developed a quantitative, stochastic, mass-balance approach to evaluate plausible scenarios of localized contamination that could explain why the soil-transmitted helminth Ascaris remains endemic despite nearly universal coverage of latrines that sequester most fecal wastes. We used microscopy to enumerate presumptively viable Ascaris ova in feces, fecal sludges, and soils from compounds (i.e., household clusters) and then constructed a steady-state mass-balance model to evaluate possible contamination scenarios capable of explaining observed ova counts in soils. Observed Ascaris counts (mean = -0.01 log10 ova per wet gram of soil, sd = 0.71 log10) could be explained by deposits of 1.9 grams per day (10th percentile 0.04 grams, 90th percentile 84 grams) of child feces on average, rare fecal sludge contamination events that transport 17 kg every three years (10th percentile 1.0 kg, 90th percentile 260 kg), or a daily discharge of 2.7 kg aqueous effluent from an onsite system (10th percentile 0.09 kg, 90th percentile 82 kg). Results suggest that even limited intermittent flows of fecal wastes in this setting can result in a steady-state density of Ascaris ova in soils capable of sustaining transmission, given the high prevalence of Ascaris shedding by children (prevalence = 25%; mean = 3.7 log10 per wet gram, sd = 1.1 log10), the high Ascaris ova counts in fecal sludges (prevalence = 88%; mean = 1.8 log10 per wet gram, sd = 0.95 log10), and the extended persistence and viability of Ascaris ova in soils. Even near-universal coverage of onsite sanitation may allow for sustained transmission of Ascaris under these conditions.

Impacts of an Urban Sanitation Intervention on Fecal Indicators and the Prevalence of Human Fecal Contamination in Mozambique

Fecal source tracking (FST) may be useful to assess pathways of fecal contamination in domestic environments and to estimate the impacts of water, sanitation, and hygiene (WASH) interventions in low-income settings. We measured two nonspecific and two human-associated fecal indicators in water, soil, and surfaces before and after a shared latrine intervention from low-income households in Maputo, Mozambique, participating in the Maputo Sanitation (MapSan) trial. Up to a quarter of households were impacted by human fecal contamination, but trends were unaffected by improvements to shared sanitation facilities. The intervention reduced Escherichia coli gene concentrations in soil but did not impact culturable E. coli or the prevalence of human FST markers in a difference-in-differences analysis. Using a novel Bayesian hierarchical modeling approach to account for human marker diagnostic sensitivity and specificity, we revealed a high amount of uncertainty associated with human FST measurements and intervention effect estimates. The field of microbial source tracking would benefit from adding measures of diagnostic accuracy to better interpret findings, particularly when FST analyses convey insufficient information for robust inference. With improved measures, FST could help identify dominant pathways of human and animal fecal contamination in communities and guide the implementation of effective interventions to safeguard health.

Safely Managed On-Site Sanitation: A National Assessment of Sanitation Services and Potential Fecal Exposure in Indonesia

Sustainable Development Goal target 6.2 calls for universal access to adequate and equitable sanitation, setting a more ambitious standard for 'safely managed sanitation services'. On-site sanitation systems (e.g., septic tanks) are widely used in low- and middle-income countries (LMICs). However, the lack of indicators for assessing fecal exposure risks presents a barrier to monitoring safely managed services. Furthermore, geographic diversity and frequency of disasters require a more nuanced approach to risk-informed decision-making. Taking Indonesia as an example, the purpose of this paper is to provide insights into current status and practices for on-site sanitation services in the contexts of LMICs. Using a dataset from a national socio-economic survey (n = 295,155) coupled with village census (n = 83,931), we assessed (1) household sanitation practices across Indonesia stratified by city-level population density and meteorological factors, (2) factors associated with septic tank emptying practice, and (3) inequalities in potential fecal exposure as measured by population density and WASH access by wealth quintile. We found a high reliance on on-site sanitation facilities (80.0%), almost half of which are assumed to be 'uncontained' septic tanks and one in ten facilities discharging untreated waste directly into the environment. The most densely populated areas had the highest rates of septic tank emptying, though emptying rates were just 17.0%, while in the lowest population density group, emptying was rarely reported. Multivariate regression analysis demonstrated an association between flooding and drought occurrence and septic tank emptying practice. Higher groundwater usage for drinking among poorer households suggests unsafe sanitation may disproportionally affect the poor. Our study underscores the urgent need to strengthen the monitoring of on-site sanitation in LMICs by developing contextualized standards. Furthermore, the inequalities in potential fecal exposure require greater attention and tailored support mechanisms to ensure the poorest gain access to safely managed sanitation services.

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.

Associations between Household-Level Exposures and All-Cause Diarrhea and Pathogen-Specific Enteric Infections in Children Enrolled in Five Sentinel Surveillance Studies

Diarrheal disease remains a major cause of childhood mortality and morbidity causing poor health and economic outcomes. In low-resource settings, young children are exposed to numerous risk factors for enteric pathogen transmission within their dwellings, though the relative importance of different transmission pathways varies by pathogen species. The objective of this analysis was to model associations between five household-level risk factors-water, sanitation, flooring, caregiver education, and crowding-and infection status for endemic enteric pathogens in children in five surveillance studies. Data were combined from 22 sites in which a total of 58,000 stool samples were tested for 16 specific enteropathogens using qPCR. Risk ratios for pathogen- and taxon-specific infection status were modeled using generalized linear models along with hazard ratios for all-cause diarrhea in proportional hazard models, with the five household-level variables as primary exposures adjusting for covariates. Improved drinking water sources conferred a 17% reduction in diarrhea risk; however, the direction of its association with particular pathogens was inconsistent. Improved sanitation was associated with a 9% reduction in diarrhea risk with protective effects across pathogen species and taxa of around 10-20% risk reduction. A 9% reduction in diarrhea risk was observed in subjects with covered floors, which were also associated with decreases in risk for zoonotic enteropathogens. Caregiver education and household crowding showed more modest, inconclusive results. Combining data from diverse sites, this analysis quantified associations between five household-level exposures on risk of specific enteric infections, effects which differed by pathogen species but were broadly consistent with hypothesized transmission mechanisms. Such estimates may be used within expanded water, sanitation, and hygiene (WASH) programs to target interventions to the particular pathogen profiles of individual communities and prioritize resources.

Urban informal settlements as hotspots of antimicrobial resistance and the need to curb environmental transmission

Antimicrobial resistance (AMR) is a growing public health challenge that is expected to disproportionately burden lower- and middle-income countries (LMICs) in the coming decades. Although the contributions of human and veterinary antibiotic misuse to this crisis are well-recognized, environmental transmission (via water, soil or food contaminated with human and animal faeces) has been given less attention as a global driver of AMR, especially in urban informal settlements in LMICs-commonly known as 'shanty towns' or 'slums'. These settlements may be unique hotspots for environmental AMR transmission given: (1) the high density of humans, livestock and vermin living in close proximity; (2) frequent antibiotic misuse; and (3) insufficient drinking water, drainage and sanitation infrastructure. Here, we highlight the need for strategies to disrupt environmental AMR transmission in urban informal settlements. We propose that water and waste infrastructure improvements tailored to these settings should be evaluated for their effectiveness in limiting environmental AMR dissemination, lowering the community-level burden of antimicrobial-resistant infections and preventing antibiotic misuse. We also suggest that additional research is directed towards developing economic and legal incentives for evaluating and implementing water and waste infrastructure in these settings. Given that almost 90% of urban population growth will occur in regions predicted to be most burdened by the AMR crisis, there is an urgent need to build effective, evidence-based policies that could influence massive investments in the built urban environment in LMICs over the next few decades.

Variation in E. coli concentrations in open drains across neighborhoods in Accra, Ghana: The influence of onsite sanitation coverage and interconnectedness of urban environments

Alongside efforts to improve safe management of feces along the entire sanitation chain, including after the toilet, global sanitation efforts are focusing on universal access 'basic' services: onsite facilities that safely contain excreta away from human contact. Although fecal sludge management is improving in urban areas, open drains remain a common fate for feces in these often densely-populated neighborhoods in low-income countries. To-date, it is unclear to what extent complete coverage of onsite sanitation reduces fecal contamination in the urban environment and how fecal contamination varies within urban drains across neighborhoods by sanitation status within a city. We assessed how neighborhood levels of environmental fecal contamination (via spatially-representative sampling of open drains for E. coli) varied across four neighborhoods with varying income, type and coverage of household sanitation facilities, and population density in Accra, Ghana. Neighborhoods with very high sanitation coverage (≥89%) still had high (>4 log10 CFU/100 mL) E. coli concentrations in drains. Between-neighborhood variation in E. coli levels among the high coverage neighborhoods was significant: drain concentrations in neighborhoods with 93% and 89% coverage (4.7 (95% CI: 4.5, 4.9) & 4.9 (95% CI: 4.5, 5.3) log10 CFU/100 mL, respectively) were higher than in the neighborhood with 97% coverage (4.1 log10 CFU/100 mL, 95% CI: 3.8, 4.4 log10 CFU/100 mL). Compared with the highest coverage neighborhood, the neighborhood with lowest coverage (48%) also had higher E. coli concentrations (5.6 log10 CFU/100 mL, 95% CI: 5.3, 5.9 log10 CFU/100 mL). Although fecal contamination in open drains appeared lower in neighborhoods with higher onsite sanitation coverage (and vice versa), other factors (e.g. fecal sludge management, animals, population density) may affect drain concentrations. These results underscore that neighborhood-level onsite sanitation improvements alone may not sufficiently reduce fecal hazards to public health from open drains. These findings supporting the need for integrated, city-level fecal sludge management alongside multifaceted interventions to reduce fecal contamination levels and human exposure.