It’s a relief that Hurricane Tomas didn’t destroy the camps in and around Port-au-Prince where 1.3 million survivors of Haiti’s January earthquake are crowded. The storm hit western Haiti hardest, causing flooding and killing 20 people.

There are still concerns about how flooding will affect Haiti’s cholera outbreak. The outbreak’s official death toll is 544, CNN reports, and more than 8,000 cholera cases have been confirmed. So far, none of the confirmed cases is in Port-au-Prince, but 91 residents of a Port-au-Prince slums are being tested to see if they’ve been infected.

Cholera outbreaks can occur when fecal matter contaminates drinking water, and floodwater from the hurricane could cause latrines and septic tanks to overflow and taint the water supply.