2016–2022 yemen cholera outbreak 2016–2022 yemen cholera outbreak an outbreak of cholera began in yemen in october 2016. the outbreak peaked in 2017 with over 2,000 reported deaths in that year alone. in 2017 and 2019, war-torn yemen accounted for 84% and 93% of all cholera cases in the world, with children constituting the majority of reported cases. as of november 2021, there have been more than 2.5 million cases reported, and more than 4,000 people have died in the yemen cholera outbreak, which the united nations deemed the worst humanitarian crisis in the world at that time. however, the outbreak has substantially decreased by 2021, with a successful vaccination program implemented and only 5,676 suspected cases with two deaths reported between january 1 and march 6 of 2021. 2016–2021 yemen cholera outbreakmap of yemen on the globediseasecholerabacteria strainvibrio choleraefirst outbreakyemeni civil warsaudi arabian–led intervention in yemensaudi blockade of yemenfamine in yemen (2016–present)datesoctober 2016–november 2021(6 years and 7 months)suspected cases‡2,510,806 through december 2020deaths3,981‡suspected cases have not been confirmed by laboratory tests as being due to this strain, although some other strains may have been ruled out. vulnerable to water-borne diseases before the conflict, 16 months went by before a program of oral vaccines was started. the cholera outbreak was worsened as a result of the ongoing civil war and the saudi arabian-led intervention in yemen against the houthi movement that began in march 2015. airstrikes damaged hospital infrastructure, and water supply and sanitation in yemen were affected by the ongoing conflict. the government of yemen stopped funding public health in 2016; sanitation workers were not paid by the government, causing garbage to accumulate, and healthcare workers either fled the country or were not paid. the unicef and world health organization (who) executive directors stated: "this deadly cholera outbreak is the direct consequence of two years of heavy conflict. collapsing health, water and sanitation systems have cut off 14.5 million people from regular access to clean water and sanitation, increasing the ability of the disease to spread. rising rates of malnutrition have weakened children's health and made them more vulnerable to disease. an estimated 30,000 dedicated local health workers who play the largest role in ending this outbreak have not been paid their salaries for nearly ten months." background scanning electron microscope (sem) image of vibrio cholerae bacteria as of 2017, yemen had a population of 25 million and was geographically divided into 22 governorates. the yemeni civil war is an ongoing conflict that began in 2015 between two factions: the internationally recognized yemeni government, led by abdrabbuh mansur hadi, and the houthi armed movement, along with their supporters and allies. both claim to constitute the official government of yemen. houthi forces controlling the capital sanaʽa, and allied with forces loyal to the former president ali abdullah saleh, have clashed with forces loyal to the government of abdrabbuh mansur hadi, based in aden. a saudi arabian-led intervention in yemen was launched in 2015, with saudi arabia leading a coalition of nine countries from the middle east and africa, in response to calls from president abdrabbuh mansur hadi for military support. cholera is an infection of the small intestine by strains of the bacterium vibrio cholerae. it is spread mostly by unsafe water and unsafe food that has been contaminated with human feces containing the bacteria. symptoms may range from none, to mild, to severe. the classic symptom is large amounts of watery diarrhea lasting a few days. diarrhea can be so severe that it leads, within hours, to severe dehydration and electrolyte imbalance. the primary treatment is oral rehydration therapy—the replacement of fluids with slightly sweet and salty solutions. in severe cases, intravenous fluids may be required, and antibiotics may be beneficial. prevention methods against cholera include improved sanitation and access to clean water. cholera vaccines that are given by mouth provide reasonable protection for about six months. two oral killed vaccines are available: dukoral and shanchol. total cost, including delivery costs, of oral cholera vaccination is under us$10 per person. outbreak visualization showing the progression of the cholera outbreak in yemen, from may 2017 – february 2018 following "on the heels of civil conflict between houthi rebels and the internationally recognized yemeni regime", the yemen cholera outbreak began in early october 2016, and by january 2017, the who regional office for the eastern mediterranean (who emro) considered the outbreak to be unusual in its rapid and wide geographical spread. the serotype of vibrio cholerae o1 involved is ougawa. the earliest cases were predominantly in the capital, sana'a, with some occurring in aden. by the end of october, cases had been reported in the governorates of al-bayda, aden, al-hudaydah, hajjah, ibb, lahij and taiz and, by late november, also in al-dhale'a and amran. by mid-december, 135 districts of 15 governorates had reported suspected cases, but nearly two-thirds were confined to aden, al-bayda, al-hudaydah and taiz. by mid-january 2017, 80% of cases were located in 28 districts of al-dhale'a, al-hudaydah, hajjah, lahij and taiz. a total of 268 districts from 20 governorates had reported cases by 21 june 2017; over half are from the governorates of amanat al asimah (the capital sana'a), al-hudaydah, amran and hajjah, which are all located in the west of the country. in particular, 77.7% of cholera cases (339,061 of 436,625) and 80.7% of deaths from cholera (1,545 of 1,915) occurred in houthi-controlled governorates, compared to 15.4% of cases and 10.4% of deaths in government-controlled governorates. using genomic sequencing, researchers at the wellcome sanger institute and institut pasteur concluded the strain of cholera originated in eastern africa and was carried to yemen by migrants. morbidity and mortality yemen authorities announced the cholera outbreak on october 7, 2016. by the end of that year, there were 96 deaths. following the october 2016 outbreak, the rate of spread in most areas declined by the end of february 2017, and by mid-march 2017, the outbreak was in decline after a wave of cold weather. a total of 25,827 suspected cases, including 129 deaths, were reported by 26 april 2017. the number of cholera cases resurged in a second wave that began on 27 april 2017. according to qadri, islam and clemens, writing in the new england journal of medicine, the dramatic april 2017 resurgence was "coincident with heavy rains that may have contaminated drinking water sources, and was amplified by war-related destruction of municipal water and sewage systems". during may 2017, 74,311 suspected cases, including 605 deaths, were reported. by june, unicef and who estimated that 5,000 new cases per day were occurring, and that the total number of cases in the country since the outbreak began in october had exceeded 200,000, with 1,300 deaths. the two agencies stated that it was then "the worst cholera outbreak in the world". by 4 july 2017, there were 269,608 cases and the death toll was at 1,614 with a case fatality rate of 0.6%. on 14 august 2017 the who updated the number of suspected cholera cases to 500,000. oxfam said in 2017 the outbreak would become the largest epidemic since record-keeping began, overtaking the 754,373 cases of cholera recorded after the 2010 haiti earthquake. in six months, more people were ill with cholera in yemen than in seven years after the earthquake in haiti, and the situation in yemen was made worse by hunger and malnutrition. on 22 december 2017, who reported the number of suspected cholera cases in yemen had surpassed one million. by october 2018, there were more than 1.2 million cases reported, and more than 2,500 people—58% children—have died in the yemen cholera outbreak, which is the worst epidemic in recorded history and was, according to the united nations (un), the worst humanitarian crisis in the world. between 1 january 2018 to 31 may 2020, the cumulative total number of suspected cases was 1,371,819 with 1566 associated deaths. the case fatality rate for the outbreak was 0.11% as of 2020, having declined from a high of 1% when the outbreak first began. causes and challenges unicef and the who attributed the outbreak to malnutrition, collapsing sanitation and clean water systems due to the country's ongoing conflict, and the approximately 30,000 local health care workers who had not been paid for almost a year. these factors resulted in a delayed vaccination program, which was not started until more than one million people were already ill. pre-civil war conditions even before civil war affected yemen, it was "beset by circumstances that made it ripe for cholera". a country with high poverty rates, yemen also suffered frequent droughts and severe water access problems, with only about half of the population having had access to good water and sanitation before the war. children under five showed a high prevalence of malnutrition, making them further susceptible to disease; yemen had "one of the highest rates of childhood malnutrition worldwide". the health care system in yemen before the conflict was weak and lacking infrastructure. for instance, before the war, 70–80% of children were vaccinated against measles, but the vaccination rate had dropped by the end of 2015. ongoing conflict because of the ongoing conflict in yemen, and resulting displacement of people who do not have adequate food, waster, housing or sanitation, pre-existing conditions were exacerbated. shortages have been made worse by naval and air blockades. bombing has damaged water and sanitation infrastructure. airstrikes have destroyed facilities in the country for health care; "half of the nation's hospitals have been either destroyed by saudi airstrikes, occupied by rebel forces, or shut down because there are no medical personnel to staff them". doctors without borders reported that a saudi arabian coalition airstrike hit a new médecins sans frontières cholera treatment center in abs, in northwestern yemen. doctors without borders reported that they had provided gps coordinates to saudi arabia on twelve separate occasions, and had received nine written responses confirming receipt of those coordinates. grant pritchard, save the children's interim country director for yemen, stated in april 2017, "with the right medicines, these are all completely treatable – but the saudi arabia-led coalition is stopping them from getting in." wastewater and solid waste management systems wastewater stabilization ponds are generally used as a primary treatment, and are inefficient at completely removing infectious agents. yemen's wastewater and solid waste management systems are the least developed among middle eastern countries, which has been a major contributor to the cholera outbreak. with 16 functional sewage treatment plants (stps) and a growing population, the country's sewage systems are ill-equipped to meet the needs of citizens and serve just 7% of the population. actual flow rates through the stps in yemen exceed the flow rates they were designed to accommodate, which reduces their efficiency. the treatment processes used are also suboptimal, with 68% of stps using only stabilization ponds - which are generally intended as a primary treatment - to remove pathogens from sewage. this has resulted in high quantities of infectious agents in effluent, which is hazardous to health and can enable the spread of cholera. moreover, wastewater in yemen is frequently reused for irrigation purposes by farmers due to a lack of awareness about safety risks. high concentrations of escherichia coli, streptococcus faecalis, klebsiella pneumoniae, enterobacter aerogenes, salmonella typhi, s. typhimurium, and shigella sonnei - among other harmful fecal coliforms - are present in this wastewater, and transmit to humans when they consume foods irrigated by it. official dumping sites for solid waste are being created increasingly close to communities, which has increased the risk of infection and general health issues among citizens. this is especially true for the roughly 70% of citizens without access to potable water, who consume water from wells near dumping sites. el niño adult chironomid the el niño–southern oscillation phenomenon is a major driver of climate variability associated with health outcomes, including influencing cholera dynamics due to changes in rainfall. for example, in east africa, there was an upsurge in cholera cases in areas with increased rainfall, along with an increase in cases in areas with decreased rainfall. in the 2015-2016 el niño event, there were an additional 50 000 cases of cholera in east africa. based on genomic approaches, there was a linkage found between the epidemic in yemen starting in 2016 and the earlier outbreaks in east africa. this alludes to