Fomite mediated transmission can be an important pathway causing significant disease transmission in number of settings such as schools, daycare centers, and long-term care facilities. The importance ...of these pathways relative to other transmission pathways such as direct person-person or airborne will depend on the characteristics of the particular pathogen and the venue in which transmission occurs. Here we analyze fomite mediated transmission through a comparative analysis across multiple pathogens and venues.
We developed and analyzed a compartmental model that explicitly accounts for fomite transmission by including pathogen transfer between hands and surfaces. We consider two sub-types of fomite-mediated transmission: direct fomite (e.g., shedding onto fomites) and hand-fomite (e.g., shedding onto hands and then contacting fomites). We use this model to examine three pathogens with distinct environmental characteristics (influenza, rhinovirus, and norovirus) in four venue types. To parameterize the model for each pathogen we conducted a thorough literature search.
Based on parameter estimates from the literature the reproductive number (Formula: see text) for the fomite route for rhinovirus and norovirus is greater than 1 in nearly all venues considered, suggesting that this route can sustain transmission. For influenza, on the other hand, Formula: see text for the fomite route is smaller suggesting many conditions in which the pathway may not sustain transmission. Additionally, the direct fomite route is more relevant than the hand-fomite route for influenza and rhinovirus, compared to norovirus. The relative importance of the hand-fomite vs. direct fomite route for norovirus is strongly dependent on the fraction of pathogens initially shed to hands. Sensitivity analysis stresses the need for accurate measurements of environmental inactivation rates, transfer efficiencies, and pathogen shedding.
Fomite-mediated transmission is an important pathway for the three pathogens examined. The effectiveness of environmental interventions differs significantly both by pathogen and venue. While fomite-based interventions may be able to lower Formula: see text for fomites below 1 and interrupt transmission, rhinovirus and norovirus are so infectious (Formula: see text) that single environmental interventions are unlikely to interrupt fomite transmission for these pathogens.
The impact of heavy rainfall events on waterborne diarrheal diseases is uncertain. We conducted weekly, active surveillance for diarrhea in 19 villages in Ecuador from February 2004 to April 2007 in ...order to evaluate whether biophysical and social factors modify vulnerability to heavy rainfall events. A heavy rainfall event was defined as 24-hour rainfall exceeding the 90th percentile value (56 mm) in a given 7-day period within the study period. Mixed-effects Poisson regression was used to test the hypothesis that rainfall in the prior 8 weeks, water and sanitation conditions, and social cohesion modified the relationship between heavy rainfall events and diarrhea incidence. Heavy rainfall events were associated with increased diarrhea incidence following dry periods (incidence rate ratio = 1.39, 95% confidence interval: 1.03, 1.87) and decreased diarrhea incidence following wet periods (incidence rate ratio = 0.74, 95% confidence interval: 0.59, 0.92). Drinking water treatment reduced the deleterious impacts of heavy rainfall events following dry periods. Sanitation, hygiene, and social cohesion did not modify the relationship between heavy rainfall events and diarrhea. Heavy rainfall events appear to affect diarrhea incidence through contamination of drinking water, and they present the greatest health risks following periods of low rainfall. Interventions designed to increase drinking water treatment may reduce climate vulnerability.
Evidence for environmental transmission of S aureus emerged in the early 1960s,12 and protocols now acknow ledge the key role of environmental management and hand hygiene, in addition to active ...surveillance, decolon isation, antibiotic stewardship, and other non-environmental controls.13 Environmental measures might prove even more crucial than expected for MRSA control in view of evidence that patients are at increased risk of acquisition if admitted to a hospital room previously occupied by a colonised patient-a clear reason for environmental disinfection.14 Importantly, these environ mental controls might need to extend outside hospital to confront the growing risk of community-acquired MRSA.15 We need to know more about the importance of the environment in direct transmission of pathogens, but one thing is clear- pathogens are present on fomites, especially during outbreaks, and these environmental surfaces should be targeted to provide an additional barrier to infection.16 As with MRSA, the balance between clinical and environmental interventions to reduce rates of some parasitic diseases has progressed substantially, especially in China.17 That country's emphasis on environmental interventions to reduce rates of schistosomiasis is especially notable.
The effectiveness of household water treatment (HWT) at reducing diarrheal disease is related to the efficacy of the HWT method at removing pathogens, how people comply with HWT, and the relative ...contributions of other pathogen exposure routes. We define compliance with HWT as the proportion of drinking water treated by a community. Although many HWT methods are efficacious at removing or inactivating pathogens, their effectiveness within actual communities is decreased by imperfect compliance. However, the quantitative relationship between compliance and effectiveness is poorly understood. To assess the effectiveness of HWT on childhood diarrhea incidence via drinking water for three pathogen types (bacterial, viral, and protozoan), we developed a quantitative microbial risk assessment (QMRA) model. We examined the relationship between log10 removal values (LRVs) and compliance with HWT for scenarios varying by: baseline incidence of diarrhea; etiologic fraction of diarrhea by pathogen type; pattern of compliance within a community; and size of contamination spikes in source water. Benefits from increasing LRVs strongly depend on compliance. For perfect compliance, diarrheal incidence decreases as LRVs increase. However, if compliance is incomplete, there are diminishing returns from increasing LRVs in most of the scenarios we considered. Higher LRVs are more beneficial if: contamination spikes are large; contamination levels are generally high; or some people comply perfectly. The effectiveness of HWT interventions at the community level may be limited by imperfect compliance, such that the benefits of high LRVs are not realized. Compliance with HWT should be carefully measured during HWT field studies and HWT dissemination programs. Studies of pathogen concentrations in a variety of developing-country source waters are also needed. Guidelines are needed for measuring and promoting compliance with HWT.
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► Household water treatment (HWT) can prevent diarrhea in developing countries. ► Increasing HWT log10 removals has diminishing returns if compliance is ≤ 99%. ► Higher HWT log10 removals prevent more diarrhea if water is highly contaminated. ► HWT compliance in communities is poorly characterized & must be carefully measured.
Background To date little conclusive evidence exists on the seasonality of rotavirus incidence in the tropics. We present a systematic review and meta-analysis on the seasonal epidemiology of ...rotavirus in the tropics, including 26 studies reporting continuous monthly rotavirus incidence for which corresponding climatological data was available. Methods Using linear regression models that account for serial correlation between months, monthly rotavirus incidence was significantly negatively correlated with temperature, rainfall and relative humidity in 65%, 55% and 60% of studies, respectively. We carried out pooled analyses using a generalized estimating equation (GEE) that accounts for correlation from between-study variation and serial correlation between months within a given study. Results For every 1°C (1.8°F) increase in mean temperature, 1 cm (0.39 in.) increase in mean monthly rainfall, and 1% increase in relative humidity (22%) this analysis showed reductions in rotavirus incidence of 10% (95% CI: 6–13%), 1% (95% CI: 0–1%), and 3% (95% CI:0–5%), respectively. Conclusions On the basis of the evidence, we conclude that rotavirus responds to changes in climate in the tropics, with the highest number of infections found at the colder and drier times of the year.
Recent results from water, sanitation, and hygiene interventions highlight the need to better understand environmental influences on enteropathogen transmission. We quantified a range of viral, ...bacterial, and protozoal pathogens and one indicator, Enterococcus faecalis in soil and water from urban and rural sites in and around Yangon, Myanmar. We found that environmental characteristics associated with contamination differed by pathogens and substrates. In soil, bacterial pathogen gene counts were associated with elevation and drainage ditches (compared to stagnant water) (RR = 0.96, 95% CI 0.93, 0.99 and RR = 1.70, 95% CI 1.18, 2.45, respectively), while viral gene counts were associated with the presence of sanitation facilities within 50 m of the collection point (RR = 3.99, 95% CI 1.12, 14.24). In water, E. faecalis, total pathogen, and bacterial pathogen gene counts were associated with drainage ditches (RR = 1.86, 95% CI 1.27, 2.72, RR = 1.38 95% CI 1.09, 1.74, and RR = 1.38 95% CI 1.07, 1.77, respectively). E. faecalis, total pathogen, bacterial pathogen, and viral gene counts were associated with the presence of uncollected garbage within 50 m of the collection point (RR = 1.57, 95% CI 1.00, 2.47, RR = 1.52, 95% CI 1.16, 2.00, RR = 1.52, 95% CI 1.13, 2.06, and RR = 1.75, 95% CI 1.17, 2.61 respectively). Measuring the environment provides added specificity toward identifying important environmental pathways that require mitigation.
Two of the most important causes of global disease fall in the realm of environmental health: household air pollution (HAP) and poor water, sanitation, and hygiene (WASH) conditions. Interventions, ...such as clean cookstoves, household water treatment, and improved sanitation facilities, have great potential to yield reductions in disease burden. However, in recent trials and implementation efforts, interventions to improve HAP and WASH conditions have shown few of the desired health gains, raising fundamental questions about current approaches.
We describe how the failure to consider the complex systems that characterize diverse real-world conditions may doom promising new approaches prematurely. We provide examples of the application of systems approaches, including system dynamics, network analysis, and agent-based modeling, to the global environmental health priorities of HAP and WASH research and programs. Finally, we offer suggestions on how to approach systems science.
Systems science applied to environmental health can address major challenges by
) enhancing understanding of existing system structures and behaviors that accelerate or impede aims;
) developing understanding and agreement on a problem among stakeholders; and
) guiding intervention and policy formulation. When employed in participatory processes that engage study populations, policy makers, and implementers, systems science helps ensure that research is responsive to local priorities and reflect real-world conditions. Systems approaches also help interpret unexpected outcomes by revealing emergent properties of the system due to interactions among variables, yielding complex behaviors and sometimes counterintuitive results.
Systems science offers powerful and underused tools to accelerate our ability to identify barriers and facilitators to success in environmental health interventions. This approach is especially useful in the context of implementation research because it explicitly accounts for the interaction of processes occurring at multiple scales, across social and environmental dimensions, with a particular emphasis on linkages and feedback among these processes. https://doi.org/10.1289/EHP7010.
Infectious disease interventions, such as vaccines and bed nets, have the potential to provide herd protection to non-recipients. Similarly, improved sanitation in one household may provide ...community-wide benefits if it reduces contamination in the shared environment. Sanitation at the household level is an important predictor of child growth, but less is known about the effect of sanitation coverage in the community.
From 2008 to 2013, we took repeated anthropometric measurements on 1314 children under 5 years of age in 24 rural Ecuadorian villages. Using mixed effects regression, we estimated the association between sanitation coverage in surrounding households and child growth.
Sanitation coverage in the surrounding households was strongly associated with child height, as those with 100% coverage in their surroundings had a 67% lower prevalence of stunting prevalence ratio (PR) 0.32, 95% CI 0.15-0.69 compared with those with 0% coverage. Children from households with improved sanitation had a lower prevalence of stunting (PR 0.86, 95% CI 0.64-1.15). When analysing height as a continuous outcome, the protective effect of sanitation coverage is manifested primarily among girls during the second year of life, the time at which growth faltering is most likely to occur.
Our study highlights that a household's sanitation practices can provide herd protection to the overall community. Studies which fail to account for the positive externalities that sanitation provides will underestimate the overall protective effect. Future studies could seek to identify a threshold of sanitation coverage, similar to a herd immunity threshold, to provide coverage and compliance targets.
Small-scale food animal production is widely practiced around the globe, yet it is often overlooked in terms of the environmental health risks. Evidence suggests that small-scale food animal ...producers often employ the use of antimicrobials to improve the survival and growth of their animals, and that this practice leads to the development of antimicrobial resistance (AMR) that can potentially spread to humans. The nature of human-animal interactions in small-scale food animal production systems, generally practiced in and around the home, likely augments spillover events of AMR into the community on a scale that is currently unrecognized and deserves greater attention. https://doi.org/10.1289/EHP2116.
Global access to safe drinking water and sanitation has improved dramatically during the Millennium Development Goal (MDG) period. However, there is substantial heterogeneity in progress between ...countries and inequality within countries.
We assessed countries' temporal patterns in access to drinking water and sanitation using publicly available data. We then classified countries using non-linear modeling techniques as having one of the following trajectories: 100% coverage, linear growth, linear decline, no change, saturation, acceleration, deceleration, negative acceleration, or negative deceleration. We further assessed the degree to which temporal profiles follow a sigmoidal pattern and how these patterns might vary within a given country between rural and urban settings.
Among countries with more than 10 data points, between 15% and 38% showed a non-linear trajectory, depending on the indicator. Overall, countries' progress followed a sigmoidal trend, but some countries are making better progress and some worse progress than would be expected. We highlight several countries that are not on track to meet the MDG for water or sanitation, but whose access is accelerating, suggesting better performance during the coming years. Conversely, we also highlight several countries that have made sufficient progress to meet the MDG target, but in which access is decelerating.
Patterns were heterogeneous and non-linearity was common. Characterization of these heterogeneous patterns will help policy makers allocate resources more effectively. For example, policy makers can identify countries that could make use of additional resources or might be in need of additional institutional capacity development to properly manage resources; this will be essential to meet the forthcoming Sustainable Development Goals.
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