Approach

In high-income countries, where Shigella sonnei is more endemic, Shigella usually presents as a mild, self-limited illness.[1]​ Medical help is not always sought, but confirmation of suspected diagnosis is usually made on the basis of stool cultures.[5]S flexneri causes a more severe illness and is more endemic in low- and middle-income countries.​

History and clinical examination

Key risk factors include exposure to contaminated water or food, direct fecal-oral contact, age <5 years, malnutrition, poor hygiene and cramped conditions, and travel to endemic areas.[2][4]​​[5]​​​[6][8][13][14]​​​​​​​​​

Diarrheal illness begins around 1-2 days after exposure.[1]​ The diarrhoea may initially be watery and profuse, but as the source is mostly colonic, it tends to be low volume.[5]​ There may be visible blood in the stool.[22]​ Abdominal cramps, fever, and tenesmus are common. Although rare, young children may experience seizures.[23] Vomiting is uncommon.[22]​ Shigella dysenteriaeand Sflexneri often cause a more severe illness, with fever and worsening bloody diarrhea with mucus. Meningism, or other signs of altered neurologic status, may indicate Shigella-induced encephalopathy. 

Clinical examination may reveal signs of volume depletion due to poor oral intake; eating or drinking appears to exacerbate the cramping abdominal pain.[5] Lower abdominal tenderness may be present, along with normal or increased bowel sounds. Toxic dilation of the colon is a consideration, as Shigella may cause severe colitis. 

Hemolytic uremic syndrome (HUS) is a severe complication. Clinical findings in children such as somnolence (due to anemia) or dry diapers (due to anuria) should raise suspicion. Stool microscopy and culture are important first-line tests to determine the cause of HUS in order to guide treatment.

Stool tests

Shigellosis is diagnosed on the basis of history, clinical features, and stool cultures. The stool culture process is stepwise. The stool sample is suspended in MacConkey agar to identify non-lactose fermenters such as Shigella species.[5] More selective media are then used, after which slide agglutination with Shigella antisera further indicates the likelihood of shigellosis. Biochemical screening tests are confirmatory for species if non-lactose fermenters are found and thought likely to be Shigella on the basis of selective media cultures and slide agglutination. [Figure caption and citation for the preceding image starts]: Stool exudates in a patient with Shigella infectionCDC [Citation ends].com.bmj.content.model.Caption@530b3d56

Shigella is a notifiable disease, and local laboratories should report confirmed cases to the appropriate public health departments or authorities. CDC: national notifiable infectious diseases surveillance system Opens in new window[13][22][24] Serotyping is useful for disease surveillance and public health.[2][13]

Other laboratory studies and imaging

Shigellosis may cause leukocytosis, especially in more severe presentations.[5] Volume depletion may be evident with rising BUN and hematocrit. It is important that HUS is not

missed.[25] Therefore, laboratory tests such as a blood smear (showing fragmentocytes) may be useful to seek this severe complication.

Abdominal x-rays may be useful if toxic dilation is suspected. In most cases, however, they are not needed, as shigellosis most often presents as a mild, self-limited illness in high-income countries. Flexible sigmoidoscopy is not usually required unless idiopathic inflammatory bowel disease is a strongly suspected differential.[26]

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