Shigellosis (Human)

Primary reference(s)

WHO, 2005. Guidelines for the control of shigellosis, including epidemics due to Shigella dysenteriae type 1. World Health Organization (WHO). Accessed 16 December 2019.

Additional scientific description

Shigellosis is clinically manifested by diarrhoea that is frequently bloody. Oher 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. Ninety-nine percent of infections caused by Shigella occur in developing countries, and the majority of cases (~70%), and of deaths (~60%), occur among children less than five years of age. Probably less than 1% of cases are treated in hospital.

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).

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

Not available.

Examples of drivers, outcomes and risk management

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). 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).

Prevention relies on measures that prevent the spread of bacteria, such as handwashing, ensuring 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).

There is no WHO-recommended vaccine that is effective for preventing infection by Shigella (WHO, 2005).