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. 2017 Nov 27;11(11):e0006103.
doi: 10.1371/journal.pntd.0006103. eCollection 2017 Nov.

The importance of thinking beyond the water-supply in cholera epidemics: A historical urban case-study

Affiliations

The importance of thinking beyond the water-supply in cholera epidemics: A historical urban case-study

Matthew D Phelps et al. PLoS Negl Trop Dis. .

Abstract

Background: Planning interventions to respond to cholera epidemics requires an understanding of the major transmission routes. Interrupting short-cycle (household, foodborne) transmission may require different approaches as compared long-cycle (environmentally-mediated/waterborne) transmission. However, differentiating the relative contribution of short- and long-cycle routes has remained difficult, and most cholera outbreak control efforts focus on interrupting long-cycle transmission. Here we use high-resolution epidemiological and municipal infrastructure data from a cholera outbreak in 1853 Copenhagen to explore the relative contribution of short- and long-cycle transmission routes during a major urban epidemic.

Methodology/principal findings: We fit a spatially explicit time-series meta-population model to 6,552 physician-reported cholera cases from Copenhagen in 1853. We estimated the contribution of long-cycle waterborne transmission between neighborhoods using historical municipal water infrastructure data, fitting the force of infection from hydraulic flow, then comparing model performance. We found the epidemic was characterized by considerable transmission heterogeneity. Some neighborhoods acted as localized transmission hotspots, while other neighborhoods were less affected or important in driving the epidemic. We found little evidence to support long-cycle transmission between hydrologically-connected neighborhoods. Collectively, these findings suggest short-cycle transmission was significant.

Conclusions/significance: Spatially targeted cholera interventions, such as reactive vaccination or sanitation/hygiene campaigns in hotspot neighborhoods, would likely have been more effective in this epidemic than control measures aimed at interrupting long-cycle transmission, such as improving municipal water quality. We recommend public health planners consider programs aimed at interrupting short-cycle transmission as essential tools in the cholera control arsenal.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Maps of epidemic in Copenhagen, 1853.
(A) The drinking-water pipe network. (B) The week number the first case was reported in each neighborhood. (C) The attack rate in each neighborhood. (D) The case-fatality rate in each neighborhood. The blue points represent hospitals, sick- and poor-houses. Map base layers and water-pipe data were digitized using QGIS from Nivellementskort over Kjöbenhavn. 1852. Archive reference: https://www.starbas.net/avmateriale.php?av_stam_id=46545.
Fig 2
Fig 2. Diagram of transmission model structure.
The boxes represent the different infection states in two neighborhoods, i and j. The solid arrows represent the different state transitions within the model, while the dotted lines represent how infectious individuals contribute to the force of infection in their own neighborhood (blue) and other neighborhoods (red).
Fig 3
Fig 3. Time-series plot of epidemic.
(A) At the city level. (B) In each neighborhood.
Fig 4
Fig 4. Median of the log of the transmission coefficients from model 3 (fully saturated model).
The diagonals represent log(βi) and off-diagonals log(αj,i). For example, row 4 (Kjoebmager), column 1 (Christianshavn) can be read as the transmission coefficient for cases arising in Kjoebmager from cases in Christianshavn. Darker blue represents higher transmission efficiency.
Fig 5
Fig 5. Result of one-step-ahead model predictions.
The mean number of new infectious cases predicted one-step-ahead with 95% prediction intervals in red. The black lines represent the 10 realizations of the epidemic used as data for parameter fitting. The vertical dotted line represents day 40 for reference between graphs.
Fig 6
Fig 6. The median outflowing, inflowing, internal, and total reproductive numbers R0 for each quarter.

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