Background: Investments in water and sanitation systems are believed to have led to the decline in typhoid fever in developed countries, such that most cases now occur in regions lacking adequate clean water and sanitation. Exploring seasonal and long-term patterns in historical typhoid mortality in the United States can offer deeper understanding of disease drivers.
Methods:We fit modified Time-series Susceptible-Infectious-Recovered models to city-level weekly mortality counts to estimate seasonal and long-term typhoid transmission. We examined seasonal transmission separately by city and aggregated by water source. We fit regression models to measure associations between long-term transmission and financial investments in water and sewer systems.Results: Typhoid transmission peaked in late summer/early fall. Seasonality varied by water source, with the greatest variation occurring in cities with reservoirs. Historical $1 per capita ($25.80 in 2017) investments in construction and operation of water and sewer systems were associated with 8-53% decreases in typhoid transmission, while $1 increases in total value or debt accrued to maintain them were associated with 4-7% decreases.
Conclusion:Our findings aid in the understanding of typhoid transmission dynamics and potential impacts of water and sanitation improvements, and can inform cost-effectiveness analyses of interventions to reduce the typhoid burden.
ABSTRACT WORD COUNT: 199geographically and historically depending on the water supply and treatment; and (2) to quantify the relationship between investments in water and sanitation infrastructures and long-term typhoid transmission rates.
METHODS
Study Design, Data, and VariablesWe extracted reported weekly typhoid mortality from 1889 to 1931 at the city level from the Project Tycho database (13, 14). Cities were chosen based on two criteria: (1) at least 1,000 typhoid deaths were reported during the study period, and (2) less than 25% of weekly data was missing. These exclusion criteria resulted in data for 16 U.S. cities ( Figure S1).Yearly population estimates were obtained from the U.S. Census Bureau (15-17). The population <1 year of age was used as a proxy for births, since birth rate data was not available and typhoid is rare in <1-year-olds (18). Cubic splines were used to extrapolate weekly population estimates. Financial data on water supply and sewer systems for each city were extracted from U.S. Census Bureau yearly reports (16); we obtained data on eight variables across five categories: "receipts," "expenses," "outlays," "total value," and "funded debt" (Table 1), divided by the yearly city population to generate per capita estimates. Data on water treatment and type for each city were extracted from a variety of sources (Table S1) (17).All cities had missing data on weekly typhoid mortality. In many cases, missing mortality counts were instances of zero cases, because cities frequently only reported during weeks when deaths occurred. To account for both true zero counts and missing data, mo...