Behavioural lapses and microbial pollution compromise the public health outcomes of safe sanitation in sustainable cities

The persistence of diarrheal diseases in urban areas, even those with ostensibly safe water and sanitation systems, indicates significant underlying microbial and infrastructural vulnerabilities that pose challenges to sustainable urban development. Kavaratti Island in India serves as a pertinent example: despite achieving universal access to desalinated water and sanitation facilities, the island reports between 250 and 500 cases of acute diarrheal disease annually. This study employs a combination of household surveys and environmental monitoring to investigate the behavioural determinants of exposure and microbial contamination across various water sources, including groundwater, ponds, and adjacent coastal waters. The findings reveal that only a quarter of households depend solely on desalinated water, while the majority continue to utilize untreated groundwater, thereby reflecting a limited understanding of the associated microbial risks. Quantitative real-time PCR analysis indicates widespread fecal contamination, with concentrations of Escherichia coli surpassing 1,000 gene copies per milliliter in all surveyed ponds and in most groundwater sources during the dry season. Furthermore, Vibrio cholerae was detected in 85% of pond samples and in 20% of groundwater samples during the rainy season. Notably, more than half of the E. coli isolates, along with all Vibrio isolates, displayed resistance to ampicillin, which is a commonly prescribed antibiotic in the region. These results illustrate that infrastructure alone is insufficient to guarantee microbial safety in vulnerable coastal urban settings. The high incidence of diarrheal disease, combined with microbial pollution and antibiotic resistance, highlights the urgent need for integrated surveillance systems, enhanced public awareness, and participatory water management strategies. Community-based initiatives, such as citizen science programs and water clinics, have the potential to strengthen public health resilience in these contexts.