Fifty people have died from cholera in the past 10 days in Senegal, about five times as many as were killed by the water-borne disease last year, and 3,700 have been infected, a health official said on Wednesday.

The latest outbreak coincided with an annual Muslim pilgrimage that draws hundreds of thousands of people to Senegal’s remote city of Touba, stretching basic health facilities and making it easier for diseases to spread.

“The disease spread quickly because of the movement of people and the lack of basic hygiene,” said the West African nation’s public health director Babacar Drame.

He said 3,700 cases were recorded between March 28 and April 6 and that the worst affected areas were central Diourbel and Kaolack, Thies in the east, and Louga in the north.

Hospital officials in Senegal’s tiny neighbor Gambia said a dozen cholera cases had been reported and two people had died since hundreds of Gambians returned from Touba. A health ministry official warned of a “looming cholera crisis.”

Last year, 11 people died from cholera in Senegal and 1,371 cases were reported, Health Ministry figures said. Across Africa, more than 1,600 people died from the disease last year, according to World Health Organization figures.

Cholera causes vomiting and diarrhea that lead to severe dehydration and death within 24 hours if treatment is not given promptly.

The disease can largely be prevented by washing hands before handling food and avoiding contaminated drinking water. Many of those who die could be saved by a simple mixture of water and rehydration salts.