Increased isolation frequency of toxigenic Vibrio cholerae O1 from environmental monitoring sites in Haiti

Abstract

Since the identification of the first cholera case in 2010, the disease has spread in epidemic form throughout the island nation of Haiti; as of 2014, about 700,000 cholera cases have been reported, with over 8,000 deaths. While case numbers have declined, the more fundamental question of whether the causative bacterium, Vibrio cholerae has established an environmental reservoir in the surface waters of Haiti remains to be elucidated. In a previous study conducted between April 2012 and March 2013, we reported the isolation of toxigenic V. cholerae O1 from surface waters in the Ouest Department. After a second year of surveillance (April 2013 to March 2014) using identical methodology, we observed a more than five-fold increase in the number of water samples containing culturable V. cholerae O1 compared to the previous year (1.7% vs 8.6%), with double the number of sites having at least one positive sample (58% vs 20%). Both seasonal water temperatures and precipitation were significantly related to the frequency of isolation. Our data suggest that toxigenic V. cholerae O1 are becoming more common in surface waters in Haiti; while the basis for this increase is uncertain, our findings raise concerns that environmental reservoirs are being established.

Fig 1. Map displaying location of environmental sampling sites from the Leogane flood basin (gray shaded region, inset) in the Ouest Department of Haiti and the source of rainfall measurements bounded by the region 18.2–18.5°N, 17.1–17.4°W (red square inset).

The environmental samples were collected between the months of April, 2013 and March, 2014. The number of V. cholerae O1 isolates obtained from each sampling site is differentiated by color.

Fig 2. The isolation frequency of both toxigenic V. cholerae O1 (red bars) and non-toxigenic V. cholerae Non-O1/O139 (gray bars) appear with respect to time overlaid with average monthly water temperature in degrees Celsius (panel A) and accumulated weekly rainfall in millimeters (panel B).