Risk reduction assessment of waterborne Salmonella and Vibrio by a chlorine contact disinfectant point-of-use device

Unsafe drinking water continues to burden developing countries despite improvements in clean water delivery and sanitation, in response to Millennium Development Goal 7. Salmonella serotype Typhi and Vibrio cholerae bacteria can contaminate drinking water, causing waterborne typhoid fever and cholera, respectively. Household water treatment (HWT) systems are widely promoted to consumers in developing countries but it is difficult to establish their benefits to the population for specific disease reduction. This research uses a laboratory assessment of halogenated chlorine beads treating contaminated water to inform a quantitative microbial risk assessment (QMRA) of S. Typhi and V. cholerae disease in a developing country community of 1000 people. Laboratory challenges using seeded well water resulted in log₁₀ reductions of 5.44 (±0.98 standard error (SE)) and 6.07 (±0.09 SE) for Salmonella serotype Typhimurium and V. cholerae, respectively. In well water with 10% sewage and seeded bacteria, the log₁₀ reductions were 6.06 (±0.62 SE) and 7.78 (±0.11 SE) for S. Typhimurium and V. cholerae, respectively. When one infected individual was contributing to the water contamination through fecal material leaking into the water source, the risk of disease associated with drinking untreated water was high according to a Monte Carlo analysis: a median of 0.20 (interquartile range [IQR] 0.017–0.54) for typhoid fever and a median of 0.11 (IQR 0.039–0.20) for cholera. If water was treated, risk greatly decreased, to a median of 4.1 × 10⁻⁷ (IQR 1.6 × 10⁻⁸ to 1.1 × 10⁻⁵) for typhoid fever and a median of 3.5 × 10⁻⁹ (IQR 8.0 × 10⁻¹⁰ to 1.3 × 10⁻⁸) for cholera. Insights on risk management policies and strategies for public health workers were gained using a simple QMRA scenario informed by laboratory assessment of HWT.