Community transmission of SARS-CoV-2 in densely populated countries has been a topic of concern from the beginning of the pandemic. Evidence of community transmission of SARS-CoV-2 according to population density gradient and socio-economic status (SES) is limited. In June–September 2020, we conducted a descriptive longitudinal study to determine the community transmission of SARS-CoV-2 in high- and low-density areas in Dhaka city. The Secondary Attack Rate (SAR) was 10% in high-density areas compared to 20% in low-density areas. People with high SES had a significantly higher level of SARS-CoV-2-specific Immunoglobulin G (IgG) antibodies on study days 1 (p = 0.01) and 28 (p = 0.03) compared to those with low SES in high-density areas. In contrast, the levels of seropositivity of SARS-CoV-2-specific Immunoglobulin M (IgM) were comparable (p > 0.05) in people with high and low SES on both study days 1 and 28 in both high- and low-density areas. Due to the similar household size, no differences in the seropositivity rates depending on the population gradient were observed. However, people with high SES showed higher seroconversion rates compared to people with low SES. As no difference was observed based on population density, the SES might play a role in SARS-CoV-2 transmission, an issue that calls for further in-depth studies to better understand the community transmission of SARS-CoV-2.

Background and Aims: Climate variability worsens waterborne diseases like diarrhea, especially in developing countries. This study investigated the link between climate factors and a diarrheal upsurge in Dhaka during May–June 2024. Methods: This cross‐sectional study was conducted in the International Center for Diarrheal Disease Research, Bangladesh (icddr,b). We considered samples from patients and climate data from May 1st to June 30th, 2024, for comprehensive analysis and comparison. We used data from icddr,b Dhaka hospital's 2% surveillance system and climate data from national aeronautics and space administration (NASA) for the same period of Dhaka city. All analyzes were conducted using R statistical software (R‐4.3.2) and a p ‐value of less than 0.05 was considered statistically significant. Results: A total of 737 patients were enrolled during May–June, with 137 cases recorded during the upsurge period from 2% of the surveillance. The most detected pathogens (10% were both vibrio cholerae and Enterotoxigenic Escherichia coli (ETEC). Cholera and also ETEC. V. cholerae was significantly ( p < 0.001) associated with age, dehydration, fever, vomiting, abdominal pain, and water source ( p = 0.003). Temperatures remained unusually high (40°C–45°C) ahead of the upsurge before dropping, coinciding with a surge in diarrhea cases. As temperatures stabilized at 30°C–32°C, cases declined. Rainfall (180 mm) and wind speed (18 km/h) peaked just prior to the upsurge, while humidity rose above 80%, coinciding with an increase in diarrhea cases. Conclusion: This study highlights how climate factors influence diarrheal disease in Dhaka and urges policymakers to prioritize climate resilience and targeted interventions.

Enterotoxigenic Escherichia coli (ETEC) harbors colonization factors (CFs) to colonize the small intestine. In this study, as part of routine systematic ETEC surveillance in Bangladesh, we evaluated CFs from ETEC isolated from hospitalized diarrheal patients using a multiplex PCR assay for the first time, as the availability of the monoclonal antibodies for dot blot assay became limited. A total of 5914 diarrheal patients were enrolled during the study period (2023-2024), and a PCR assay, targeting heat-labile toxin (LT) and heat-stable toxin (ST), found 531 ETEC-infected patients. In our findings, 40 % of the ETEC isolates were positive for ST, followed by 38 % for LT + ST and 22 % for LT. The overall CF detection rate by using newly established multiplex PCR was 51 % among the ETEC-positive cases. CFA/I + CS21, CS6 ± CS21, CS5 + CS6, and CS1 + CS3 + CS21 were the most prevalent CFs in that period. For validation purposes, the multiplex PCR assay was compared to the conventional dot blot method, considered the gold standard. Both assays were used in parallel to assess the frequency of CFs detected in a subset of ETEC strains (n = 157). We observed a significant consistency between the dot blot and the PCR method. Additionally, compared to the dot blot method, the PCR assay identified CS21 in 11 % more ETEC strains harboring CFA/I or CS6. Overall, our findings suggest the multiplex PCR method is advantageous as well as time-efficient for detection of ETEC CFs compared to the dot blot assay.

Enterotoxigenic Escherichia coli (ETEC) cause hundreds of millions of diarrheal illnesses annually ranging from mildly symptomatic cases to severe, life-threatening cholera-like diarrhea. Although ETEC are associated with long-term sequelae including malnutrition, the acute diarrheal illness is largely self-limited. Recent studies indicate that in addition to causing diarrhea, the ETEC heat-labile toxin (LT) modulates the expression of many genes in intestinal epithelia, including carcinoembryonic cell adhesion molecules (CEACAMs) which ETEC exploit as receptors, enabling toxin delivery. Here however, we demonstrate that LT also enhances the expression of CEACAMs on extracellular vesicles (EV) shed by intestinal epithelia and that CEACAM-laden EV increase in abundance during human infections, mitigate pathogen-host interactions, scavenge free ETEC toxins, and accelerate ETEC clearance from the gastrointestinal tract. Collectively, these findings indicate that CEACAMs play a multifaceted role in ETEC pathogen-host interactions, transiently favoring the pathogen, but ultimately contributing to innate responses that extinguish these common infections. Significance statement: Enterotoxigenic E. coli, characterized by the production of heat-labile (LT) and heat-stable (ST) toxins, are a very common cause of diarrhea in low-income regions responsible for hundreds of millions of infections each year, and the major cause of diarrhea in travelers to endemic areas. Although these infections may be severe and cholera-like, they are typically self-limited. These studies demonstrate that extracellular vesicles produced by host intestinal cells can capture the bacteria and its secreted toxins at a distance from the cell surface, potentially acting as molecular decoys to neutralize the enterotoxins and extinguish the infection.

Bacteriophages (phages) likely play a critical role in modulating transmission dynamics of diarrheal pathogens. This study investigated the role of phages in modulating the prevalence and seasonal patterns of major diarrheal pathogens, Vibrio cholerae O1 (VCO1), enterotoxigenic Escherichia coli (ETEC), Shigella spp., and Salmonella spp. in diarrheal patients and environmental wastewater specimens collected from six different sites in Dhaka, Bangladesh, in 2024. VCO1, ETEC, Shigella , and Salmonella were detected in 10.1%, 7.8%, 1.7%, and 2.4% of diarrheal specimens, respectively. In contrast, phages targeting these pathogens were more frequently isolated, with detection rates of 20% for VCO1, 30% for ETEC, 57% for Shigella , and 9.2% for Salmonella -specific phages. Adults showed a significantly higher burden of VCO1 and corresponding phages compared with children <5 years ( P < 0.001). Seasonal analysis revealed significant correlations between VCO1 (37.3%) and corresponding phages (57.6%) peaking in late September in both clinical ( r = 0.53, P < 0.0001) and environmental wastewater specimens ( r = 0.65, P < 0.001). The highest correlation (r = 0.68) was found between the increased rate of wastewater phages in the preceding week and a rise in cholera cases in the following week. ETEC and ETEC phages isolated from wastewater also showed strong correlations ( r = 0.65, P < 0.001). Cross-specificity analysis demonstrated that VCO1 phages were highly specific to their targets, whereas ETEC and Shigella phages exhibited broader host ranges, with some Shigella phages capable of infecting ETEC and Salmonella spp. Overall, these findings support the hypothesis that Vibrio phages could serve as an alternative or complementary tool for cholera surveillance. IMPORTANCE: Understanding the dynamics between phages and their bacterial hosts is critical for elucidating disease burden; however, their potential for surveillance remains underexplored. To our knowledge, this is the first study that longitudinally investigated major diarrheal pathogens and their phages in both clinical and environmental sources to assess the potential of bacteriophages as a tool to improve diarrheal surveillance. The high frequency of phages compared to the host bacterial counterparts suggests a valuable, yet underutilized, role for phages in surveillance systems. Strong seasonal alignment between V. cholerae O1 and its phages, both peaking in late September, suggests that phage dynamics may reflect pathogen transmission. These preliminary observations raise the possibility that wastewater-derived Vibrio phages could function as early indicators of cholera burden. Future research should aim to explore the complex and poorly understood interactions between phages and their bacterial hosts, particularly how these dynamics shape pathogen populations in endemic settings.

Background: The dynamics of humoral immune responses following primary and booster COVID-19 vaccinations are crucial to understand in order to optimize vaccination strategies. This study evaluates the magnitude and durability of SARS-CoV-2-specific IgG antibody responses across different vaccines in a large cohort of Bangladeshi adults. Methods: A total of 6300 adults from nine hospitals across eight divisions of Bangladesh were enrolled. Participants received two primary doses of either ChAdOx1 nCoV-19 (Covishield, Serum Institute of India, n = 2855), mRNA-1273 (Moderna, n = 578), BNT162b2 (Pfizer-BioNTech, n = 121), or Vero-cell-inactivated (Sinopharm, n = 2746) vaccines. Booster doses were administered at one-year intervals post-primary vaccination. SARS-CoV-2 spike receptor-binding domain (RBD)-specific IgG antibody responses were measured by ELISA using serum from vaccinees at multiple time points after two primary and two booster doses. Results: A total of 3745 individuals received booster 1 (third dose), with 59% receiving heterologous boosters (a different vaccine regimen than the primary doses). Only 5.5% (n = 347) of participants received a second booster one year after the first booster (among them, 99% received BNT162b2). Our results suggest that heterologous boosters with the mRNA vaccine induced higher IgG levels than homologous boosters for individuals who received primary vaccination with adenovirus vector-based ChAdOx1 nCoV-19 or a Vero-cell-inactivated vaccine. However, in those who initially received the mRNA-based vaccine, both homologous and heterologous boosters produced comparable IgG responses. Among all vaccine types, booster immunization with the Vero-cell-inactivated vaccine induced the lowest antibody responses. Longitudinal analysis demonstrated significantly high IgG levels over the 12 months following the first booster (p < 0.0001); however, IgG levels declined significantly after the second booster dose (fourth dose). Conclusions: Heterologous boosting strategies, particularly those involving mRNA vaccines, elicit stronger and more sustained IgG responses compared to a homologous booster. However, antibody waning after the second booster highlights the need for continued monitoring and potential additional vaccine strategies.