Seasonal Trends, Environmental Drivers, and Lessons Learned From the 2023 Cholera Outbreak in Chattogram, Bangladesh:...

Acute watery diarrhea (AWD) remains a major global public health problem, and cholera continues to cause substantial morbidity and mortality in settings with inadequate water, sanitation, and hygiene (WASH). Chattogram, a coastal district of Bangladesh, is particularly vulnerable due to seasonal hydroclimatic changes, salinity intrusion, and high population density. On May 6, 2023, an increase in AWD cases was reported, prompting an outbreak investigation. We aimed to describe the epidemiology, identify the causative pathogens and source, assess environmental contributors, examine seasonal trends, and recommend preventive measures.

We conducted a descriptive investigation from May 7 to May 15 2023, in two tertiary hospitals, two Upazila Health Complexes, and affected communities. Five-year historical data were reviewed to assess seasonal patterns, and facility-based surveillance data from April 2023 were analyzed. Active community case finding, standardized interviews, environmental assessments, stool culture and sensitivity testing, and water-quality testing for coliforms, Vibrio cholerae, and salinity were performed.

Between April 1 and May 15 2023, 7956 AWD hospital admissions were reported, with sustained transmission during the pre-monsoon period. Among 166 interviewed patients, adults aged 18-40 years were most affected (65/166, 39%); all had AWD, and 85% (141/166) reported vomiting. Six (6) of 23 stool cultures yielded V. cholerae. Coliform was detected in two (2) of three (3) tube wells and all pond samples, while non-O1/non-O139 V. cholerae was identified in multiple water sources. Salinity ranged from 210 to 2320 mg/L, with several sources exceeding recommended limits. Urban cases mainly relied on intermittent piped water, whereas rural households depended on tube wells and contaminated surface water with low treatment practices.

The outbreak was associated with unsafe and saline water, intermittent supply, and inadequate household water treatment. Strengthening climate-resilient water systems, routine water-quality monitoring, sanitation, and pre-monsoon preparedness is essential to prevent recurrent cholera-associated AWD outbreaks in coastal Bangladesh.