Researchers led by Shaoqiang Li and Zihui Wang assembled data from 201 countries and territories spanning 1990 to 2021, drawing on the Global Burden of Disease Study, the World Health Organization Global Health Observatory, the World Bank, the Organization for Economic Co-operation and Development and the NCD Risk Factor Collaboration. Their broader screen covered 182 candidate exposures, of which 26 relevant to multidrug-resistant tuberculosis were reported in detail across the domains of air pollution, nutrition, sanitation, education and physical activity. Because the exposures of interest are difficult to measure reliably in individuals but are well recorded at the population level, the team used a two-stage ecological estimator that first adjusted each outcome for sex ratio, diabetes and HIV/AIDS, then regressed the adjusted residual on each candidate exposure in turn.

The global picture they describe is starkly uneven. Prevalence of multidrug-resistant tuberculosis ranged from 0.0003 to 0.2173 per thousand across countries in 1990, and by 2021 the spread had widened to between 0.0001 and 1.256 per thousand. The five countries with the highest prevalence in 2021 were Somalia, Eswatini, Eritrea, Lesotho and Mozambique, all in sub-Saharan Africa, while Slovenia, Andorra, Barbados, Iceland and San Marino sat at the bottom with rates below 0.0006 per thousand. Of an estimated 1.11 million prevalent cases in 2021, South Asia accounted for 56.2 percent and sub-Saharan Africa for 21.6 percent, followed by Southeast Asia, East Asia and Eastern Europe. Men consistently showed higher prevalence and mortality than women, a gap that widened with advancing age, and rates rose with age in both sexes.

The strongest associations in the analysis belonged to factors that had never before been linked to drug-resistant tuberculosis in the published literature. Unsafe sanitation topped the ranking, with a one-interquartile-range increase in exposure corresponding to 13.9 additional prevalent cases per 100,000 people, followed by unsafe water sources at 11.2 and polluting cooking fuels at 10.7. The same three factors led for mortality, at 2.87, 2.74 and 2.64 deaths per 100,000 respectively. Absence of handwashing facilities, household air pollution from solid fuels, iron deficiency, vitamin A deficiency and several dietary components, including diets low in fruits, vegetables and calcium, also emerged as previously unreported correlates. Air pollution and mean years of schooling, by contrast, had already been flagged in earlier studies.

The mechanistic reasoning behind these findings draws on individual-level evidence that the ecological design itself cannot test. Poor sanitation facilitates faecal-oral transmission of enteric infections, which may drive chronic gut inflammation and systemic immune suppression. Air pollution damages the respiratory mucosal barrier, impairs ciliary function and promotes oxidative stress, and laboratory work has shown that exposing human mononuclear cells to fine particulate matter reduces their capacity to control the growth of Mycobacterium tuberculosis and suppresses interferon-gamma production. Nutrition operates through two distinct pathways: malnutrition impairs macrophage function, T-cell activation and antibody production, increasing the likelihood that latent infection progresses to active disease, and undernutrition also alters the absorption and distribution of first-line tuberculosis drugs, a pharmacokinetic variability that by itself can select for resistance even in patients whose adherence is complete.

Correlation patterns across age and sex added further texture to the results. Associations grew stronger in successively older age groups, a trend that held for 25 of the 26 exposure-outcome pairs and is consistent with cumulative exposure over a lifetime and with the slower clearance of the tuberculosis bacterium reported in aged hosts. Correlations were higher in women than in men for 23 of the 26 pairs, yet on the absolute scale the increment per interquartile range of exposure was larger in men for 22 of the pairs, reflecting their higher baseline rates of disease. The demographic distribution of the burden itself remained stable across the three decades studied, with the excess in men plausibly reflecting greater occupational exposure, smoking and alcohol consumption, and clustered occupations such as mining and construction in high-burden settings.

A crucial control comparison qualified the interpretation. When the team repeated the analysis with drug-susceptible tuberculosis as the outcome, the associations were as strong or stronger for every factor except diet low in fruits. Standardized to each outcome’s own mean, the ratio of the multidrug-resistant to the drug-susceptible estimate was 0.78 for unsafe sanitation, 0.60 for polluting cooking fuels and 0.51 for vitamin A deficiency, while diet low in fruits stood at 1.04, the only factor associated more strongly with resistant disease. This pattern suggests that the identified conditions relate to tuberculosis burden as a whole rather than to drug resistance specifically, which carries significant implications for how control programmes are designed.

Sensitivity analyses tested how robust the findings were to socioeconomic confounding. After adjustment for gross domestic product per capita and health expenditure, six of the thirteen principal exposures remained significant for prevalence: unsafe sanitation, unsafe water source, absence of handwashing facilities, underweight, iron deficiency and diet low in fruits. The same six held when the Socio-demographic Index replaced the two economic covariates, and polluting cooking fuels additionally remained significant for mortality. Estimates were attenuated under this adjustment, with unsafe sanitation falling from 13.9 to 2.8 cases per 100,000 per interquartile range, but the authors note that these exposures are themselves strongly correlated with national income, at a median absolute Spearman coefficient of 0.86, so the adjustment removed much of the exposure’s own variation. Results varied by less than 13 percent across exposure windows of 5, 10, 15 and 20 years.

The regional decomposition reveals that the two areas carrying most of the burden face very different exposure profiles. South Asia, with 56.2 percent of prevalent cases, showed its largest excesses in diet low in fruits, underweight and iron deficiency, while sub-Saharan Africa, with 21.6 percent of cases but 32.2 percent of deaths, was furthest above the global median for absence of handwashing facilities, underweight and household air pollution from solid fuels. The authors emphasize that the same interventions would therefore not address both regions equally, and that because correlations were strongest in the oldest age groups, older adults in these two regions are where burden and exposure coincide most closely. Eastern Europe presents a telling exception: it carries 5.6 percent of prevalent cases with a population-weighted exposure excess of only 0.03 interquartile ranges, yet has the highest multidrug-resistant proportion of tuberculosis of any region, pointing to treatment and health-system factors that this design could not measure.

The authors are candid about the limitations inherent in an ecological study of this scale. Previous treatment history, treatment adherence and drug-susceptibility testing coverage, the factors with the largest established effects on resistance, have no complete country-year series across 201 countries over three decades. Associations identified through contrasts between countries cannot be read as effects in individuals, and both outcomes and many exposures are modelled estimates that share covariates and smoothing assumptions. National income also determines both the exposures and the capacity to detect resistant disease, warranting caution about directionality. Nevertheless, the six associations that survived socioeconomic adjustment are the least likely to be explained away by such confounding, and the findings align directionally with individual-level evidence, including a cluster-randomized trial in India in which nutritional supplementation among household contacts reduced tuberculosis incidence by 39 to 48 percent. The practical implication is that water, sanitation and clean-cooking programmes are already working on the very conditions most strongly associated with the resistant tuberculosis burden, and there is a case for planning tuberculosis control and environmental health interventions together rather than treating them as separate enterprises.

Subject of Research: Population-level environmental and nutritional factors associated with multidrug-resistant tuberculosis across 201 countries from 1990 to 2021

Article Title: Identifying overlooked factors associated with multidrug-resistant tuberculosis: an ecological study across 201 countries and regions, 1990–2021

Article References: Identifying overlooked factors associated with multidrug-resistant tuberculosis: an ecological study across 201 countries and regions, 1990–2021. (n.d.). https://doi.org/10.1016/j.jare.2026.10.028

Image Credits: AI Generated

DOI: Not provided

Keywords: multidrug-resistant tuberculosis, sanitation, air pollution, nutrition, Global Burden of Disease, cooking fuels, iron deficiency, vitamin A deficiency, handwashing, South Asia, sub-Saharan Africa, ecological study

The study, led by Abiot Abera Aydamo of the Ethiopian Institute of Water Resources at Addis Ababa University and Wachemo University, together with Sirak Robele Gari and Seid Tiku Mereta, was designed to overcome a persistent weakness in the childhood diarrhea literature. Most studies in developing countries, including Ethiopia, have relied on cross-sectional surveys that capture a single snapshot in time, making it difficult to distinguish whether risk factors precede illness or merely coincide with it. By following the same households prospectively across seasons and recording each new diarrheal episode as it occurred, the Hosanna team could measure incidence directly and track how exposure to specific hazards translated into disease over time. The research covered three kebeles, the smallest administrative units in Ethiopia, chosen to represent the peri-urban and informal settlements that ring many fast-growing Ethiopian towns.

Data collection combined three complementary methods. Caregivers, primarily mothers, answered a pretested structured questionnaire covering household characteristics, water handling, sanitation, and child care practices. Trained observers conducted spot-check observations of household conditions, a technique that helps verify what families report with what can actually be seen in the home environment, from the cleanliness of water storage containers to the presence of handwashing stations. Finally, a dedicated diarrhea recording questionnaire allowed caregivers to log each episode of illness as it happened, reducing the recall bias that plagues surveys asking parents to remember illnesses weeks or months in the past. This triangulation of self-report, observation, and longitudinal symptom tracking is what gives the study its unusual analytical power for a resource-constrained setting.

On the statistical side, the researchers deployed two modeling approaches. Bivariate logistic regression provided an initial screen of associations, while the core analysis relied on Generalized Estimating Equations, or GEEs. The choice was deliberate and technically meaningful. Where mixed-effects models estimate subject-specific effects, essentially asking how a risk factor changes the trajectory for a particular child, GEEs estimate population-averaged effects, asking how a risk factor shifts the expected disease burden across the whole community. For public health planning, that population-averaged framing is often the more useful one, because interventions such as extending piped networks or running handwashing campaigns operate at the community scale rather than for individual children one at a time. The results were expressed as adjusted incidence rate ratios, or AIRRs, which quantify how much each factor multiplies the rate of diarrheal episodes after accounting for other variables.

The risk factor hierarchy that emerged is striking in its coherence. Children in households with piped water located off the premises, meaning families had to fetch water from taps or standpipes outside the home, experienced 1.57 times the incidence rate of diarrhea compared with children whose homes had water on premises. Unsafe disposal of child stool raised the rate by a factor of 1.47, and children who ate unheated leftover food faced a 1.43-fold increase. The single largest behavioral hazard was poor handwashing by caregivers at critical moments, such as before preparing food, before feeding a child, and after using the latrine or cleaning a child, which was associated with an adjusted incidence rate ratio of 1.95, nearly doubling the rate of illness. Each of these factors represents a well-established pathway by which fecal pathogens travel from the environment into a young child’s mouth, but seeing them quantified together in a single longitudinal cohort, with seasonal coverage, sharpens the picture considerably.

Water quality itself told an equally important story. The team tested household drinking water for Escherichia coli, the standard bacterial indicator of fecal contamination, and found that children drinking contaminated water suffered significantly more diarrhea during both the dry and rainy seasons. That seasonal consistency matters. In many settings, water quality deteriorates dramatically during the rains, when runoff washes waste into shallow wells and unprotected springs, and the rainy season is typically when diarrhea cases surge. But the Hosanna data show that contamination is not merely a wet-weather problem; households drawing E. coli-laden water face elevated risk year-round. This suggests that household water treatment, whether boiling, chlorination, or filtration, could deliver benefits across every season, and that the dry-season contamination likely reflects persistent problems in storage, handling, and source protection rather than episodic weather-driven events alone.

Age emerged as a powerful and protective axis in the analysis. Children aged 24 to 35 months and 36 to 59 months had significantly reduced risk of diarrhea compared with younger children, a pattern consistent with the immunology and behavior of early childhood. Infants and toddlers who are crawling, teething, and exploring their environment by mouth are exposed to far more environmental pathogens, and their immune systems are still naive to the rotating cast of viruses and bacteria that cause gastroenteritis. As children grow older, improved motor control, more adult-like eating habits, and accumulating immunity all push risk downward. The finding reinforces a message that pediatric and water researchers have long emphasized: the window from birth to roughly two years of age is when water, sanitation, and hygiene interventions pay their largest dividends, and it is exactly the window in which the Hosanna cohort shows the heaviest disease burden.

Not all the news in the study is grim. Better hygienic practices were found to be protective against childhood diarrhea, confirming that the behavioral side of the equation works in both directions. Just as poor handwashing at critical times nearly doubles incidence, consistent hygiene practices measurably reduce it. This bidirectional evidence base strengthens the case for hygiene promotion programs that go beyond infrastructure, targeting the specific moments when pathogens are most likely to jump from hands, food, or utensils into a child. The study’s authors argue that improving on-premises water access, promoting mothers’ handwashing at critical times, encouraging household water treatment, and strengthening hygiene and food safety practices are all essential levers for reducing diarrheal disease in settings like Hosanna, and their data provide the incidence estimates and effect sizes needed to model what such interventions might achieve.

The broader significance of the work lies in what it says about peri-urbanization. Hosanna Town, like many secondary cities across Ethiopia and sub-Saharan Africa, is growing faster than its water and sanitation infrastructure can expand. Families settling in informal and peri-urban neighborhoods often live within a few hundred meters of a piped network yet remain unconnected, forced to fetch water in quantities too small for generous hygiene and to store it in containers that invite recontamination. The 2.2 versus 1.0 episodes-per-year contrast between unconnected and connected households is a direct measure of what that infrastructure gap costs in child health. For a disease that remains a leading cause of illness and death among children under five in developing countries, an intervention that halves incidence simply by delivering water to the household tap represents one of the most cost-effective public health opportunities available.

The study received ethical approval from Ethiopia’s National Research Ethics Review Committee under the Ministry of Education and was conducted in accordance with the Declaration of Helsinki, with written consent obtained from the mothers and caregivers of all participating children. It was supported by the Ethiopian Institute of Water Resources at Addis Ababa University and Wachemo University. The authors state that the findings provide evidence to guide interventions aimed at reducing childhood diarrhea in Ethiopia and other developing countries, and the longitudinal design gives that evidence a durability that single-snapshot surveys cannot match. As governments and donors weigh investments in water infrastructure against competing priorities, the Hosanna cohort offers a concrete, quantified answer to a deceptively simple question: what happens to child health when clean water finally reaches the home? The answer, measured episode by episode over a full year of dry seasons and rains, is that the burden of childhood diarrhea drops by half, and the pathogens that stalk the youngest children lose their most reliable ally.

Subject of Research: Incidence and risk factors of diarrhea among under-five children in peri-urban central Ethiopia

Article Title: Incidence of caregiver-reported diarrhea and associated risk factors among under-five children in Hosanna Town, central Ethiopia: a prospective cohort study

Article References: Aydamo, A. A., Gari, S. R., & Mereta, S. T. (2026). Incidence of caregiver-reported diarrhea and associated risk factors among under-five children in Hosanna Town, central Ethiopia: a prospective cohort study. BMC Pediatrics. https://doi.org/10.1186/s12887-026-07776-5

Image Credits: AI Generated

DOI: 10.1186/s12887-026-07776-5

Keywords: diarrhea, under-five children, Ethiopia, piped water, water access, handwashing, E. coli, prospective cohort study, water sanitation and hygiene, child health, peri-urban settlements, food safety

Hygiene is a cornerstone of public health. Poor hygiene is closely tied to infection, disease transmission, and preventable illness, which is why public health researchers have long sought to understand the psychological drivers of behaviors such as handwashing, housecleaning, and personal grooming. Decades of work on disgust—the emotion thought to have evolved as a behavioral defense against pathogens—have established that people who are more easily disgusted tend to engage in more protective hygiene behavior. At the same time, olfaction has repeatedly been implicated in this picture: the sense of smell is our most direct chemical sensor of the environment, capable of detecting spoilage, contamination, and body odors that signal potential health threats.

The new research set out to connect these threads more rigorously. Rather than treating olfaction as a single, undifferentiated capacity, the team distinguished between olfactory metacognition—how people think and feel about their own sense of smell—and olfactory function measured objectively in the laboratory. The central hypothesis was that olfactory functioning relates to hygiene behavior at least partly through disgust sensitivity, the tendency to experience revulsion in response to potential contaminants. To test this, the researchers conducted two studies with distinct designs and measurement approaches.

Study 1 recruited 270 participants and focused on three indicators of olfactory metacognition: odor awareness, the subjective importance people attach to their sense of smell, and self-rated olfactory ability. Each of these indicators was positively associated with self-reported hygiene behavior. Crucially, when the researchers used mediation analysis to examine indirect pathways, each indicator showed a significant indirect effect through disgust sensitivity. In other words, people who were more attuned to odors, who valued their sense of smell more highly, and who rated their olfactory ability as stronger also tended to report higher disgust sensitivity—and that heightened disgust, in turn, was associated with more frequent and thorough hygiene practices.

These findings align with a conceptual framework in which disgust functions as part of the so-called behavioral immune system, a suite of psychological mechanisms that guard against disease threat before pathogens ever reach the body. According to this view, sensory inputs—especially smells—provide cues about potential contamination, and disgust converts those cues into avoidance and cleaning behavior. The Study 1 results suggest that individual differences in how prominently smell figures in daily awareness may shape the intensity of this disgust-based defense, and thereby the vigor of one’s hygiene routine.

But subjective self-reports are not the same as measured sensory ability. Study 2 therefore extended the investigation with 66 participants who completed psychophysical odor-threshold testing and suprathreshold ratings for one pleasant and one unpleasant odor. This design allowed the researchers to ask whether the ability to detect faint odors—rather than merely one’s beliefs about one’s own nose—also relates to hygiene behavior, and whether the valence of the odor matters. The results were more nuanced here. Odor sensitivity itself was not directly associated with hygiene behavior, a finding that echoes earlier work suggesting that disgust sensitivity relates to affective responses to odors rather than to the raw capacity to detect them.

Yet the indirect pathway through disgust sensitivity did appear in Study 2, though selectively. A significant indirect effect through disgust sensitivity was observed for the pleasant odor but not for the unpleasant odor. That an unpleasant smell failed to show the same pathway may seem counterintuitive, but the authors caution that a bootstrap comparison did not support a statistically reliable difference between the two indirect effects. In other words, the apparent pleasant-versus-unpleasant asymmetry at the threshold level should be interpreted with care, as the data could not confirm that the two odor conditions truly differed in the strength of this mediated pathway.

Where odor-condition differences did emerge clearly was at the suprathreshold level—when participants judged clearly perceivable odors. The associations of hygiene behavior with odor pleasantness and familiarity differed significantly between the pleasant and unpleasant odor conditions, with positive associations observed specifically for the pleasant odor. This suggests that how people appraise and contextualize everyday smells—their emotional coloring and their sense of familiarity—may relate to hygiene behavior differently depending on the hedonic character of the odor in question, whereas simple detection ability appears less consequential.

Taken together, the two studies paint a differentiated picture: subjective and psychophysical aspects of olfactory functioning are related to hygiene behavior in partly different ways. Disgust sensitivity emerges as one affective correlate of these associations, providing a plausible psychological route by which smelling and thinking about smells translates into washing, cleaning, and grooming. Meanwhile, odor valence effects were more clearly supported for conscious appraisal of suprathreshold odors than for basic odor sensitivity, implying that the emotional meaning of smell, rather than the acuity of the nose per se, drives much of the connection to hygiene.

The findings carry practical weight for public health. If disgust sensitivity mediates the link between olfaction and hygiene behavior, interventions aimed at improving hygiene might benefit from strategies that engage the sense of smell and the emotion of disgust together—approaches that earlier experimental and field-based work on hand hygiene has begun to explore. At the same time, the authors emphasize limits: the indirect pathway was not uniformly observed across odor conditions, the pleasant-versus-unpleasant asymmetry in threshold-based mediation was not statistically reliable, and the data underlying the study will be shared only on reasonable request to the corresponding author. Future research with larger and more diverse samples will be needed to determine when, and for whom, the nose-disgust-hygiene pathway operates most strongly—and whether it can be harnessed to promote healthier behavior at the population scale.

Subject of Research: The relationship between olfactory functioning, disgust sensitivity, and hygiene behavior

Article Title: Disgust sensitivity as an indirect pathway linking olfactory functioning and hygiene behavior

Article References: Jiang, C., Modi, U., & Han, P. (2026). Disgust sensitivity as an indirect pathway linking olfactory functioning and hygiene behavior. Current Psychology, 45(17), Article 1487. https://doi.org/10.1007/s12144-026-10057-0

Image Credits: AI Generated

DOI: 10.1007/s12144-026-10057-0

Keywords: olfaction, disgust sensitivity, hygiene behavior, odor awareness, olfactory metacognition, odor threshold, odor valence, behavioral immune system, public health, psychology, sensory perception, handwashing