Cholera epidemiology and demographics

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editors-In-Chief: Sara Mehrsefat, M.D. [2], Tarek Nafee, M.D. [3], Priyamvada Singh, MBBS [4]Ahmed Younes M.B.B.CH [5]

Overview

In 2015, 172,454 cases and 1,304 deaths of cholera were reported to WHO worldwide. Outbreaks continued to affect several countries. Overall, 41% of cases were reported from Africa, 37% from Asia, and 21% from the Americas. In the early 1980s, mortality rates are believed to exceeded 3 million deaths a year. It is difficult to calculate exact numbers of cases, as many go unreported due to concerns that an outbreak may have a negative impact on the tourism of a country. Cholera remains both epidemic and endemic in many areas of the world. Although much is known about the mechanisms behind the spread of cholera, this has not led to a full understanding of what makes cholera outbreaks happen some places but not others. Lack of adequate treatment of human feces and/or drinking water greatly facilitates the spread of cholera. Bodies of water can serve as a reservoir of the disease. Seafood shipped over long distances can also spread the disease. Cases of cholera were not observed in the Americas for most of the 20th century, thought the disease reappeared towards the end of that century and seems likely to persist.

2017 Yemen outbreak

Date	Cases (confirmed and suspected)	Deaths	More details
June 11th, 2017	101,820	791 (0.7%)	Since the outbreak started in April 27, 2017, a total of 101,820 cases were suspected from which 791 died. Most of the fatalities are children below 15 years (46% of cases) and elderly over 60 years (33% of cases). The disease is spreading in 19 out of 23 governorates in the country that is war torn. The health system in the country is nearly destroyed which makes the mission to control the disease even harder. After 2 years of conflict, less than half of the healthcare centers are working. Medical supplies are entering Yemen in a rate that is third of what it used to be before the conflict. Moreover, infrastructure is terribly damaged preventing 14.5 million people from having access to clean water and sanitation. Efforts by WHO and UNICEF are made to control the outbreak especially in the “hotspots” or the most affected areas. 66.7 million US dollars are invested in the fight against the outbreak. Till the moment, 3.5 million people have been reached through disinfecting water tanks, chlorination of water and distributing hygiene kits.
June 25th, 2017	200,000	1300 (0.65%)	Number of suspected cases has doubled so has the number of dead, making it the worst cholera outbreak in the recent history. Numbers are expected to rise in the next few weeks. WHO and UNICEF are scaling up their efforts to contain the outbreak. Rapid response teams are going from house to house educating people about the effective measures for primary and secondary prevention. Local health workers (estimated 30,000 of them) have not been paid for 10 months due to the ongoing conflict and economic crisis, making the efforts to contain the infection more difficult.
July 2nd, 2017	246,000	1500 (0.6%)	WHO is paying incentives to the local health workers who have not been paid for 10 months. WHO is setting up treatment centers in 10 governorates with the capacity of 50 each. Centers will be working around the clock in the efforts to fight the epidemic.
July 10th, 2017	297,438	1706 (0.57%)	After 10 weeks of the outbreak, the international committee of the red cross has declared that the recent outbreak is a disaster added to the economic collapse and the near famine in Yemen. The daily growth of the cases has decreased to 2%. However, new outbreak hotspots are discovered. The west region is the area most affected by the outbreak and that is due to the continuous war there. The spread of the disease is thought to be limited due to acquistion of “herd immunity” by the population from surviving patients. The mortality rate is controlled due to the early catching of the disease and the abundant network of rehydration points.
July 16th, 2017	326,082	1,743 (0.53%)	The outbreak has spread to 91% of the yemeni governorates. The plans to deploy cholera vaccines were suspended. According to WHO spokesperson, priority now comes to the measures to stop the progress of the outbreak such as ensuring clean water supply and treating patients. Up till now, about 2300 diarrhea treatment centers and 700 oral rehydration facilities were set up in the efforts to stop the spread of the outbreak. The limited numbers of vaccine doses can not cover the whole country and can cause more disputes between different regions of the country. This was another reason to suspend the plans to deploy the vaccines. Up till now, 42% of the infected population are children below 15 years and 32% of the deaths are 60 years or above.
July 22nd, 2017	462, 545	1817 (0.39%)	Cholera cases is now over 360,000 cases in three months only. The epidemic is declared the worst (in terms of the cases per one year) since the start of the modern recording system (highest number was in Haiti in 2011 and it recorded 340, 311 cases/year). Oxfam estimates that the number of cases might rise above 600,000 cases making it the worst epidemic since 1949. Unicef states that most of the children do not have access to clean water or the proper medical care and that 17 million Yemenis do not know from where they are getting their next meal. Distribution of cholera cases per 1000 people on July 17 - Source: http://www.who.int/en/
July 29th, 2017	408,583	1,885 (0.46%)	The rate of daily infected cases is now dropping and so is the case fatality rate. The outbreak is thought to have peaked 3 weeks ago. Despite the slowing of the spread, the number of daily cases remains high (5,000 to 6,000 cases per day) and the outbreak remains one of the worst in the recent history. The WHO is preparing for a massive campaign of vaccination in 2018 using 500,000 doses of oral cholera vaccine. WHO is targeting not only Yemen, but also Somalia, Kenya, Congo, Nigeria, Tanzania and South Sudan where cholera remains a concern.
August 5th, 2017	453,175	1,930 (0.42%)	Estimates that one million children are acutely malnourished with one fifth of them has severe malnutrition. Malnourished children are three times more at risk to contract the infection because of the reduced immunity. Children below 15 years account for 44% of the new cases and 32% of the deaths. Source: http://www.who.int/en/
August 12th, 2017	473,701	1,953 (0.41%)	The outbreak is now affecting 96% (22/23) governorates and 89% (297/333) districts. Seventy Percent of Yemen’s 28 million population live in these affected areas. The overall number of suspected cases have been declining in the past five weeks, however, it has reached a plateau stage in the top 4 governorates affected. An epidemic curve showing the weekly number of cases during the first wave (in 2016) and the second wave (in 2017) of the outbreak - Source: http://www.who.int/en/ The figures show the distribution of cases by age and sex. The right most figure shows the percentage of the different outcomes of suspected cases -Source: http://www.who.int/en/ The map on the left shows the total number of cases in the different governorates while the map on the right shows the attack rate per 10,000 people in the same governorates - Source: http://www.who.int/en/
September 5th, 2017	607,065	2,047 (0.34%)	The number of cases hit the 600,000 mark. This is the double of the WHO estimates for the worst case scenario in April. The number of cases has been falling in August but some districts report sharp increase in the number of suspected cases for the past two weeks. WHO investigates if the new rise of cases is due to cholera or due to another diarrheal illness. With the continuation of civil war, nearly 16 million Yemenis are deprived of clean water and proper sanitation.
September 29th, 2017	754,373	2,119 (0.28%)	The outbreak is declared as the worst recorded cholera outbreak after the number of suspected cases exceeded the Haiti outbreak of 2010. There number of cases are expected to reach one million by November this year. Source: http://www.who.int/en/

Epidemiology and Demographics

Incidence

• In 2015, 172,454 cases and 1,304 deaths of cholera were reported to WHO worldwide. Outbreaks continued to affect several countries.
• Overall, 41% of cases were reported from Africa, 37% from Asia, and 21% from the Americas.
• Worldwide, cholera affects an estimated 1.4 to 4.3 million people and causes 28,000 to 142,000 deaths a year as of 2012.

Origin and Spread

Cholera was originally endemic to the Indian subcontinent, with the Ganges River likely serving as a contamination reservoir. It spread by trade routes (both land- and sea-based) to Russia, then to Western Europe, and from Europe to North America. Cholera is no longer considered an issue in Europe and North America, due to filtering and chlorination of the water supply.

Gender

Cholera occurs equally in males and females.

Age

• In non-endemic areas, cholera occurs equally in all age groups.
• In endemic regions, children older than the age of 2 years are most commonly infected which cholera. Illness is uncommon before children reach 2 years of age, likely due to passive immunity.

Geographic Distribution

Cholera in the United States

In the United States, the occurrence of cholera is very low (0-5 cases per year) and is usually due to ingestion of contaminated food or infection during international travel. There has been a modest increase in imported cases since 1991 related to travel and ongoing epidemics.

Cholera in the Developing World

The highest incidencce of cholera in the developing world occurs in the following regions:

• Africa: Zambia, Mozambique, Liberia, Democratic Republic of Congo, Niger
• Asia: Indonesia, Bangladesh, India
• The Americas: Dominican Republic, Haiti
• The Middle East: Yemen

Source: http://www.who.int/en/

Source: http://www.who.int/en/

Case Fatality Rates

• In 2015, the case fatality rates (CFRs) for cholera ranged from 0.0% to 11.7%; globally, the overall CFR was 0.8%.
• CFRs >1% were reported by 15 countries.
  • Of these 15 countries, CFR >5% were reported in Myanmar and Niger.
  • In Yemen, the case-fatality rate is reported to be between 4% to 5%.
• The average case fatality rate for Europe and the Americas is estimated to be around 1%.
• At the Treatment Center of the International Center for Diarrheal Disease Research in Bangladesh, less than 1% of patients with severe dehydration die.
• In Africa, a marked decline in case fatality rates has reported since 1970.
• in South America, low case fatality rates have been achieved.