Estimating the Transmission Potential of Symptomatic and Asymptomatic Cholera Cases from Household Microbiological and Clinical Data.

Background: In Bangladesh, cholera treatment focuses on acute watery diarrhea in symptomatic cases at health facilities, though asymptomatic infections are common. Understanding the role of asymptomatic infections in transmission is crucial for designing appropriate control strategies in this setting. Methods: We utilized data from household studies conducted in Dhaka, Bangladesh during 2006-2018 where a symptomatic confirmed cholera case and their household contacts were followed for thirty days. Vibriocidal antibodies, bacteriological culture, and symptom histories were collected at multiple times points. We used a hidden Markov model to estimate risk of infection from intra-household and extra-household (i.e., community and environmental) sources and to quantify relative risk of transmission from symptomatic and asymptomatic infected household contacts. Results: Estimated daily risk of intra-household infection from a symptomatic individual to another household member was 2.6% (95% CI: 0.4% - 5.6%) and from an asymptomatic infected individual to another household member was 1.6% (95% CI: 0.2% - 4.5%). We found no significant differences in probability of infection from asymptomatic compared to symptomatic individuals (OR: 0.60; 95% CI: 0.11 - 3.23). We estimated that daily risk of infection from extra-household sources during follow-up was 1.0% (95% CI: 0.7% - 1.4%). Conclusion: Mitigation measures focused solely on treatment of symptomatic cholera cases may be insufficient to prevent transmission in a household. This supports use of interventions that reduce risk of transmission irrespective of symptoms, such as prophylactic antibiotic treatment for household members and/or providing safe water and hygiene kits following a confirmed household or community case.