Epidemiology and transmission factors
The disease occurs when the pathogen enters the gastrointestinal tract. The incubation period varies significantly: it can be as short as 6–12 hours in massive infection or extend up to 5–7 days, although most commonly the first symptoms appear on days 2–3.
Infection occurs under conditions favorable for the fecal-oral mechanism. When taking the epidemiological history, special attention is paid to the following factors:
- Alimentary route: consumption of food that has not undergone sufficient heat treatment (raw milk and dairy products, cold appetizers, salads, as well as unwashed fresh berries, vegetables, and fruits).
- Waterborne route: drinking unboiled water, especially from open or questionable water bodies.
- Sanitary and hygienic factor: non-compliance with basic personal hygiene rules, staying in an area with an unfavorable epidemiological situation for shigellosis, unsanitary conditions (lack of equipped toilets, heavy fly infestation.
The severity of the course and the risk of chronicity are significantly influenced by prior gastrointestinal pathologies that impair its barrier function. Such aggravating factors include previously suffered salmonellosis, foodborne toxicoinfections, protozoan infestations (amebiasis, balantidiasis, giardiasis), helminthiases, as well as chronic non-infectious lesions (gastritis, cholecystitis, pancreatitis, enterocolitis).
Clinical presentation of the colitic variant
The development of acute shigellosis generally begins abruptly. General intoxication rapidly increases in the patient, accompanied by a rise in body temperature to subfebrile or febrile levels (up to 38.6 °C and above) during the first three days.
Local symptoms are caused by the development of an inflammatory process in the cecum and, particularly, in the sigmoid colon. Patients complain of intense abdominal pain, false urges to defecate, and severe tenesmus. A pronounced dynamic change in stool characteristics is typical:
- At the beginning of the disease, the stool may be frequent, loose, relatively voluminous, with visible admixtures of mucus and blood.
- As the inflammation progresses, the volume of feces decreases sharply. The stool becomes scant, acquires a fecal-free character, and consists predominantly of mucus with streaks of fresh blood.
During physical examination and deep gliding palpation of the abdomen, a clear clinical marker is revealed: the sigmoid colon is palpated as a painful, dense, and markedly spastic cord.
Clinical Forms
To accurately establish a comprehensive clinical diagnosis, the disease must be classified according to the syndromic principle. The following main variants of the course of acute shigellosis are distinguished:
- Colitic (classic, with dominating symptoms of distal large intestine damage).
- Gastroenterocolitic (combined lesion of the stomach, small and large intestine, combining vomiting, profuse diarrhea, and subsequent development of colitis syndrome).
- Gastroenteric (predominant manifestation of gastroenteritis symptoms, often requiring differential diagnosis with foodborne toxicoinfections and viral diarrheas).
Laboratory and instrumental diagnostics
Confirmation of the diagnosis is based on the detection of the pathogen itself, its antigens, or specific antibodies, as well as on the assessment of the morphological state of the intestinal mucosa.
- Bacteriological method: considered the gold standard. Consists of inoculating feces onto specialized diagnostic nutrient media followed by isolation of the Shigella culture.
- Serological diagnostics:
- IHA (indirect hemagglutination assay): allows the detection of specific antibodies in the patient's blood serum. The result becomes positive by the end of the first week from the onset of symptoms, and by the end of the second week, a diagnostically significant titer rise is observed.
- Coagglutination test: aimed at searching for Shigella antigens (in coprofiltrates, urine, saliva, or as part of circulating immune complexes). The method is highly informative from the first days of the disease.
- Instrumental methods (sigmoidoscopy): the method has auxiliary significance. Endoscopic visualization reveals various forms of proctosigmoiditis: from catarrhal and catarrhal-hemorrhagic to erosive and ulcerative.
In complex clinical situations, differential diagnosis is required. For example, in mixed infections, it is important to distinguish the symptoms of acute shigellosis from the initial manifestations of intestinal amebiasis (caused by Entamoeba histolytica). Unlike amebiasis, in which the pain syndrome is localized predominantly on the right and the onset is usually gradual, shigellosis manifests acutely with left-sided pain and characteristic scant bloody-mucous stool (whereas the full-blown clinical picture of amebiasis typically features "raspberry jelly" stool).
Briefly: answers to topical questions
What infectious diarrheas require differential diagnosis with shigellosis?
Differential diagnosis of shigellosis, according to the cited sources, is performed with infections and conditions presenting with a similar intestinal syndrome:
- Amebiasis — the sources state that amebiasis is differentiated primarily from shigelloses; it is also noted that the clinical picture of shigellosis is uncharacteristic for the initial stage of amebic dysentery.
- Salmonellosis — a shorter acute phase is described for them compared to shigelloses.
- Foodborne toxicoinfections (FTI).
- Yersiniosis.
- Escherichiosis.
- Enteritis of viral etiology.
- Campylobacteriosis as infectious gastroenteritis of another etiology.
- Dyspeptic variant of the initial period of botulism, in which differential diagnosis is difficult.
Which species of bacteria of the genus Shigella are the main causative agents of the disease in humans?
The cited sources name the following Shigella species:
- Shigella flexneri;
- S. zonne;
- S. newcastle;
- Shigella Grigorova–Shiga;
- Shigella Flexneri and Sonnei.
Pathogenicity factors are indicated for Shigella in the sources: adhesiveness, enteroinvasiveness, colicinogenicity, enterotoxigenicity, and cytopathogenicity.
Which groups of antibacterial drugs are used for etiotropic treatment of shigellosis?
For etiotropic treatment of shigellosis, the cited sources indicate:
- Furazolidone — for mild cases.
- Fluoroquinolones: ofloxacin, ciprofloxacin — for moderate and severe cases.
- 2nd generation cephalosporins: cefuroxime — in combination with fluoroquinolones in severe cases.
- 3rd generation cephalosporins: ceftazidime or cefoperazone — in combination with fluoroquinolones in severe cases.
- Ampicillin and nalidixic acid — for Grigorova–Shiga shigellosis.
- Rifaximin — for adults and children over 12 years old.
It is also indicated that combinations of two or more drugs are strictly limited to severe cases, and etiotropic treatment is not indicated for the gastroenteritic variant.
What specific complications can develop in severe shigellosis?
The sources attribute the following to specific complications of shigellosis:
- Infectious-toxic shock (ITS).
- Acute adrenal insufficiency.
- Intestinal perforation and peritonitis.
- Encephalic syndrome — in children and immunocompromised patients.
- Rectal prolapse is predominantly seen in children.
- Hemolytic uremic syndrome (HUS).
Other intestinal and local complications of shigellosis include: intestinal hemorrhage, hemorrhagic infiltration of the ileal wall, toxic megacolon, intestinal paresis, intestinal obstruction, intussusception, fistulas, intestinal gangrene, pericolitis, paraproctitis, anal sphincter fissures, and cicatricial stenosis of the intestine.
Shigellosis features the four S's: Spastic Sigmoid colon, Scanty Stool with Slime.
Class and exam questions
Within what timeframe does a positive indirect hemagglutination assay (IHA) result appear in shigellosis?
Specific antibodies in blood serum can be detected using the passive hemagglutination test starting from the end of the first week of the disease, with their maximum titer reached by the end of the second week.
How does the stool in the colitic variant of shigellosis clinically differ from that in cholera or rotavirus?
Unlike watery diarrhea with voluminous stools lacking pathological impurities, typical shigellosis is characterized by frequent yet scanty stool devoid of fecal matter (resembling a "rectal spit") mixed with mucus and fresh blood streaks.
Which part of the intestine is predominantly affected in acute shigellosis?
The primary target is the distal large intestine. On abdominal palpation, the most pronounced changes (tenderness, induration, spasm) are found in the projection of the sigmoid colon.
What else to study on this topic
- Clinical differences between gastroenterocolitic and gastroenteritic variants of shigellosis
- Differential diagnosis of shigellosis from intestinal amebiasis and balantidiasis
- Complications of shigellosis and mechanisms of infection chronicity
- Principles of interpreting sigmoidoscopy results in diarrheal syndromes
- The role of mixed infections (e.g., a combination of shigellosis with asymptomatic amoebic carriage) in clinical practice
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