Modeling the effect of water, sanitation, and hygiene and oral cholera vaccine implementation in Haiti

Abstract

In 2010, toxigenic Vibrio cholerae was newly introduced to Haiti. Because resources are limited, decision-makers need to understand the effect of different preventive interventions. We built a static model to estimate the potential number of cholera cases averted through improvements in coverage in water, sanitation and hygiene (WASH) (i.e., latrines, point-of-use chlorination, and piped water), oral cholera vaccine (OCV), or a combination of both. We allowed indirect effects and non-linear relationships between effect and population coverage. Because there are limited incidence data for endemic cholera in Haiti, we estimated the incidence of cholera over 20 years in Haiti by using data from Malawi. Over the next two decades, scalable WASH interventions could avert 57,949-78,567 cholera cases, OCV could avert 38,569-77,636 cases, and interventions that combined WASH and OCV could avert 71,586-88,974 cases. Rate of implementation is the most influential variable, and combined approaches maximized the effect.

Figure 1.

Total (n = 663,134) cholera cases by week, Haiti, October 20, 2010–June 30, 2013.

Figure 2.

Coverage-effectiveness curves for various interventions. Black line indicates oral cholera vaccine; dark gray dotted line indicates piped water; gray dotted-dashed line indicates point-of-use chlorination; light gray dashed line indicates latrines.

Figure 3.

Cumulative cases of cholera averted by water, sanitation and hygiene (WASH) interventions, oral cholera vaccine interventions (OCV) or a combination of both (Combi) over a 20-year period in Haiti, and assuming a baseline national cholera incidence rate from Malawi (1990–2010) applied to urban and rural Haiti.

Figure 4.

Cumulative cases of urban (U) cholera cases averted by water, sanitation and hygiene (WASH/U1), oral cholera vaccine (OCV/U1) and a combination of WASH and OCV (Combined/U 1) scenarios when 20-year baseline annual incidence data from Malawi (1990–2010), Mozambique (1990–2010) and India (1961–1981) are applied to Haiti demographic data.

Figure 5.

Cumulative cholera cases averted over 20 years in Haiti by combined water, sanitation and hygiene (WASH) and oral cholera vaccine (OCV) intervention scenarios. The x-axis refers to OCV coverage at year 5, and the different lines refer to the proportion of total piped water coverage (10%, 20%, 30%, 40%, and 50%) at year 20. We assumed that 1) persons who received OCV would not be covered by WASH interventions and vice versa; 2) WASH and OCV interventions never exceed 50%, respectively; 3) point-of-use chlorination increases from 20% (urban), or 26% (rural) and will remain the same until piped water takes over (provided assumption 1 met); 4) latrine coverage remains 10% until it is taken over by point-of-use chlorination or piped water; 5) piped water baseline = 0% in rural areas and 10% in urban areas, and piped water coverage starts increasing at a constant rate from year 6 onwards; and 6) OCV coverage increases at a constant rate from 1% baseline at year 0, peaks at year 5 and decreases thereafter at a constant rate to reach 5% at year 20.