Shigellosis
Shigellosis is an acute invasive enteric infection caused by bacteria belonging to the genus Shigella and is estimated to cause at least 80 million cases of bloody diarrhoea and 700,000 deaths each year (WHO, 2005).
Primary reference(s)
WHO, 2005. Guidelines for the control of shigellosis, including epidemics due to Shigella dysenteriae type 1. World Health Organization (WHO). Accessed 08 March 2025.
Annotations
Additional scientific description
Shigellosis is clinically manifested by diarrhoea that is frequently bloody. Other common symptoms are abdominal cramps and tenesmus (unproductive, painful straining), fever and loss of appetite (WHO, 2005). The majority of cases and deaths are among children less than five years of age (WHO, 2005).
Shigellosis is endemic in many developing countries and also occurs in epidemics causing considerable morbidity and mortality. It is estimated to cause at least 80 million cases of bloody diarrhoea and 700,000 deaths each year (WHO, 2005). Ninety-nine percent of infections caused by Shigella occur in developing countries, and the majority of cases (~70%), and deaths (~60%), occur among children less than five years of age). Probably less than 1% of cases are treated in hospital (WHO, 2005).
Shigella are Gram-negative, non-motile bacilli belonging to the family Enterobacteriacae. The genus Shigella includes four species: S. dysenteriae, S. flexneri, S. boydii and S. sonnei, also designated groups A, B, C and D, respectively. The first three species include multiple serotypes. S. sonnei and S. boydii usually cause relatively mild illness in which diarrhoea may be watery or bloody. S. flexneri is the chief cause of endemic shigellosis in developing countries. Immunity is serotype-specific. Among the four species of Shigella, Shigella dysenteriae type 1 (Sd1) is especially important because it causes the most severe disease and may occur in large regional epidemics. Major obstacles to the control of shigellosis include the ease with which Shigella spreads from person to person and the rapidity with which it develops antimicrobial resistance (WHO, 2005).
All species of Shigella cause acute bloody diarrhoea by invading and causing patchy destruction of the colonic epithelium. This leads to the formation of micro-ulcers and inflammatory exudates and causes inflammatory cells (polymorphonuclear leucocytes, PMNs) and blood to appear in the stool. The diarrhoeal stool contains 106-108 Shigellae per gram. Once excreted, the organism is very sensitive to environmental conditions and dies rapidly, especially when dried or exposed to direct sunlight (WHO, 2005).
Although most infections with S. sonnei result in a short duration of disease and low case fatality, multi-drug resistant (MDR) and XDR shigellosis is a public health concern since treatment options are very limited for moderate to severe cases (WHO, 2022).
Definitive diagnosis can only be made by isolating the organism from stool and serotyping the isolate. Culture is also required to determine antimicrobial sensitivity (WHO, 2005).
The World Health Organization (WHO) has published guidance on case classification and surveillance standards (WHO, 2005).
Metrics and numeric limits
Among children younger than 5 years, it is estimated that diarrhoea is responsible for about 446 000 deaths, which are geographically concentrated in sub-Saharan Africa and South Asia.
Shigella was the second-leading cause of diarrhoeal mortality in 2016 among all ages, and the leading bacterial cause of diarrhoea, accounting for approximately 212 000 deaths and about 13% of all diarrhoea-associated deaths (Khalil et al., 2018).
The greatest burden is among children in low- and middle-income countries (LMICs), where it is estimated to be responsible for between 28 000 (Maternal Child Epidemiology Estimation (MCEE) estimates) and 64 000 (Institute for Health Metrics and Evaluation (IHME) estimates) deaths among children under 5 years of age (Khalil et al., 2018; Lanata et al., 2013).
It is also an important cause of diarrhoea with or without dysentery in people older than 5 years, with an estimated 270 million episodes occurring annually among all ages (WHO, no date a).
Key relevant UN convention / multilateral treaty
International Health Regulations (2005), 3rd ed. (WHO, 2016).
Drivers
Outbreaks of bloody diarrhoea due to Sd1 are most common in overcrowded, impoverished areas with poor sanitation, inadequate hygiene practices, and unsafe water supplies. Refugees and internally displaced persons are at especially high risk (WHO, 2005). It is spread by direct contact with an infected person, or by eating contaminated food or drinking contaminated water. Flies may also transmit the organism (WHO, 2005).
Shigellosis is endemic in most developing countries and is the most important cause of bloody diarrhoea worldwide. Some groups of people are more likely to get sick with shigellosis than others and include: children younger than 5 years old are the most likely to get shigellosis, but people of all ages can get the disease - with many outbreaks occur in early care and education settings and schools; travellers to places where water and food may be unsafe and sanitation is poor are more likely to get a Shigella infection - they are also more likely to become sick with types of Shigella that are more difficult to treat; gay, bisexual, and other men who have sex with men (GBMSM) have factors that put them at increased risk for Shigella infection - and although rates are higher among GBMSM, the risk is present for any sexual activity involving stool exposure; and people who are experiencing homelessness are at high risk for Shigella infection when there is shigellosis spread in the community - as they may face challenges in their living situations that increase the risk for disease transmission, which can result in outbreaks (CDC, no date).
Impacts
Prompt detection and reporting of cases of bloody diarrhoea is the essential first step in the monitoring of endemic shigellosis and in the control of epidemic shigellosis. The number of cases of bloody diarrhoea, and of deaths associated with bloody diarrhoea, should be determined and reported for two age groups: under five years, and five years or older. Each health facility should designate a specific individual to be responsible for reporting all cases of, and deaths associated with, bloody diarrhoea. Reports should be provided each week to the district health officer responsible for monitoring the occurrence of cases and detecting outbreaks. For surveillance and reporting purposes, the standard case definition of bloody diarrhoea or dysentery is ‘diarrhoea with visible blood in the stool’ (WHO, 2005).
Multi-hazard context
Shigellosis is endemic in most developing countries and is the most important cause of bloody diarrhoea worldwide. Some groups of people are more likely to get sick with shigellosis than others and include: children younger than 5 years old are the most likely to get shigellosis, but people of all ages can get the disease – with many outbreaks occur in early care and education settings and schools; travellers to places where water and food may be unsafe and sanitation is poor are more likely to get a Shigella infection - they are also more likely to become sick with types of Shigella that are more difficult to treat; gay, bisexual, and other men who have sex with men (GBMSM) have factors that put them at increased risk for Shigella infection – and although rates are higher among GBMSM, the risk is present for any sexual activity involving stool exposure; and people who are experiencing homelessness are at high risk for Shigella infection when there is shigellosis spread in the community – as they may face challenges in their living situations that increase the risk for disease transmission, which can result in outbreaks (CDC, no date).
Risk Management
Prevention relies on measures that prevent the spread of bacteria, such as handwashing, ensuring the availability of safe water, safe human waste disposal, breastfeeding of infants and young children, safe handling and processing of food and control of flies (WHO, 2005).
Treatment options for shigellosis include antimicrobials. The rise of antimicrobial-resistant enteric bacteria, particularly Shigella, means that, in addition to the potential direct effects on morbidity and mortality, a Shigella vaccine might also have indirect effects on reducing the use of antibiotics and the consequent emergence of antimicrobial resistance (AMR). Considering the potential for herd immunity and protection from all-cause diarrhoea, the development of a Shigella vaccine is an important goal for public health (WHO, no date).
Although several candidate Shigella vaccines are being evaluated at different stages of preclinical and clinical development, currently no licensed vaccines against Shigella diarrhoea are widely available. Development of Shigella vaccines has been identified as priority by the independent standing WHO committee of experts for the Product Development for Vaccines Advisory Committee (WHO, no date c) and WHO Preferred Product Characteristics (PPCs) (WHO, no date d) for a safe, effective and affordable vaccine to reduce mortality and morbidity due to dysentery and diarrhoea caused by Shigella in children under 5 years of age, in LMICs are being finalized (WHO, no date).
Monitoring
The geographical spread of XDR S. sonnei is under-reported. WHO advises national authorities to reinforce Shigella surveillance including testing for antimicrobial resistance to detect potential introductions to new areas and to prevent the establishment of local cycles of transmission in communities (WHO, 2022).
WHO supports countries to conduct all-hazards strategic risk assessment in the contexts of health emergencies and disasters, which results in the development of a country's risk profile. Empowered with the country risk profile, inclusive of a seasonal risk calendar, countries can anticipate potential emergencies before they occur to trigger early alerts and inform early actions (WHO, 2021).
WHO's Early Warning, Alert and Response System (EWARS) has been designed to improve disease outbreak detection in emergency settings, such as in countries in conflict or following a natural disaster. It is a simple and cost-effective way to rapidly set up a disease surveillance system. EWARS is deployed during an emergency as an adjunct to the national disease surveillance system. WHO works with Ministries of Health and health sector partners to train local health workers to use the system. After the emergency, EWARS should re-integrate back into the national system (WHO, no date b).
References
CDC, no date. About Shigella Infection. Centers for Disease Control and Prevention (CDC). Accessed 18 April 2025.
Khalil, I.A., Troeger, C., Blacker, B.F., Rao, P.C., Brown, A., Atherly, D.E., Brewer, T.G., Engmann, C.M., Houpt, E.R., Kang, G., Kotloff, K.L., Levine, M.M., Luby, S.P., MacLennan, C.A., Pan, W.K., Pavlinac, P.B., Platts-Mills, J.A., Qadri, F., Riddle, M.S., Ryan, E.T., Shoultz, D.A., Steele, A.D., Walson, J.L., Sanders, J.W., Mokdad, A.H., Murray, C.J.L., Hay, S.I., Reiner, R.C. Jr., 2018. Morbidity and mortality due to shigella and enterotoxigenic Escherichia coli diarrhoea: the Global Burden of Disease Study 1990-2016. Lancet Infect Dis. 18(11):1229-1240. doi: 10.1016/S1473-3099(18)30475-4. Epub 2018 Sep 25. Erratum in: Lancet Infect Dis. 2018 Dec;18(12):1305. doi: 10.1016/S1473-3099(18)30664-9. PMID: 30266330; PMCID: PMC6202441. Accessed 29 May 2025.
Lanata, C.F., Fischer-Walker, C.L., Olascoaga, A.C., Torres, C.X., Aryee, M.J., Black, R.E., 2013. Child Health Epidemiology Reference Group of the World Health Organization and UNICEF. Global causes of diarrheal disease mortality in children <5 years of age: a systematic review. PLoS One. 8(9):e72788. doi: 10.1371/journal.pone.0072788. PMID: 24023773; PMCID: PMC3762858. Accessed 29 May 2025.
WHO, 2005. Guidelines for the control of shigellosis, including epidemics due to Shigella dysenteriae type 1. World Health Organization (WHO). Accessed on 25 May 2025.
WHO, 2016. International Health Regulations (2005), 3rd ed. World Health Organization (WHO). Accessed 13 February 2025.
WHO, 2021. Strategic toolkit for assessing risks (STAR): a comprehensive toolkit for all-hazards health emergency risk assessment. World Health Organization (WHO). Accessed 13 February 2025.
WHO, 2022. Extensively Drug-Resistant Shigella sonnei Infections - Europe.” Disease Outbreak News, 24 March 2022, World Health Organization (WHO). Accessed 9 May. 2025.
WHO, no date a. Shigella (Immunization, Vaccines and Biologicals). Accessed 15 February 2025.
WHO, no date b. Early Warning, Alert and Response System (EWARS). World Health Organization (WHO). Accessed 18 April 2025.
WHO, no date c. Product Development for Vaccine Advisory Committee. World Health Organization (WHO). Accessed 25 May 2025.
WHO, no date d. Preferred Product Characteristics and Target Product Profiles, World Health Organization (WHO). Accessed 25 May 2025.