The cholera outbreak began in early October 2016. The World Health Organization (WHO) considers the outbreak to be unusual in its rapid and wide geographical spread. The earliest cases were predominantly in the capital, Sana'a, with some occurring on the northern coast. By the end of October, cases had been reported in the governorates of Al-Bayda,
By the end of February 2017, the rate of spread in most areas had reduced, and by mid-March 2017, the outbreak was in decline. A total of 25,827 suspected cases, including 129 deaths, had been reported by 26 April 2017.
The number of cholera cases resurged after 27 April 2017. During May, 74,311 suspected cases, including 605 deaths, were reported. By 24 June 2017, UNICEF and WHO estimated that the total number of cases in the country since the outbreak began in October had exceeded 200,000, with 1,300 deaths, and that 5,000 new cases a day were occurring. The two agencies stated that it was then "the worst cholera outbreak in the world". Approximately half of the cases, and a quarter of the deaths were among children.
As of 12 June 2017, the case fatality rate for the outbreak is 0.7%, with higher rates in people over 60 years old (3.2%). The serotype of Vibrio cholerae involved is Ougawa. A total of 268 districts from 20 of the country's 23 governorates had reported cases by 21 June 2017; over half are from the governorates of Amanat Al Asimah (the capital Sana'a), Al Hudeideh, Amran and Hajjah, which are all located in the west of the country.
WHO, UNICEF, the International Committee of the Red Cross (ICRC) and Médecins Sans Frontières are among the organisations providing assistance.
UNICEF and WHO attributed the outbreak to malnutrition and collapsing sanitation and clean water systems due to the country's ongoing conflict. An ICRC worker in