Shigellosis 

Updated: Aug 20, 2021
Author: Heba Rashid Ashraf, MD; Chief Editor: BS Anand, MD 

Overview

Practice Essentials

Shigellosis is a diarrheal infection caused by Shigella species—gram-negative, non-spore forming, facultative anaerobes that infect the intestinal lining—and spread by fecal-oral transmission. Shigellosis is a major public health problem in both developed and underdeveloped countries, especially with increasing resistance to first- and second-line antimicrobial agents.[1, 2]

Signs and symptoms

Symptoms of shigellosis include the following:

  • Acute bloody diarrhea

  • Abdominal cramping

  • Tenesmus

  • Urgency

  • Fever

  • Occasional vomiting

  • Dehydration

These symptoms are usually self-limiting and can last from 2 to 7 days. However, certain populations are at an increased risk of severe shigellosis infection, including children in daycare, incarcerated persons, international travelers, homosexual men, people infected with human immunodeficiency virus (HIV), and those who live in crowded, unsanitary conditions.

See Presentation for more detail.

Diagnosis

Stool culture should be obtained in all suspected cases of shigellosis. Specimens should be processed immediately after collection. Ova and parasite stool studies should be collected to rule out other causes of infectious diarrhea such as Entamoeba histolytica and parasitic worms. Other laboratory tests, such as a white blood cell (WBC) count, may be performed in persons with severe symptoms or to rule out other causes. Creatinine and blood urea nitrogen (BUN) should be monitored to assess the hydration status of the patient.

See Workup for more detail.

Management

Maintain hydration to compensate for fluid losses from diarrhea.

Antibiotic treatment is indicated in most patients with a positive stool culture for Shigella. Treatment can reduce symptoms by 2 days.

Indications for treatment per Centers for Disease Control and Prevention (CDC) recommendations include persons who work in public setting (ie, food handlers, childcare providers, residents of nursing homes), have a immunocompromised state (including individuals with HIV), and patients with severe disease (those who require hospitalization or have complications). Patients infected with Shigella may shed the bacteria for up to 6 weeks, even after resolution of symptoms.[3]

Avoid the use of antimotility agents, because they have the potential to worsen the symptoms and may predispose to toxic dilatation of the colon.

Clear liquids followed by a low residue, lactose-free diet are recommended until symptoms of shigellosis resolve.

See Treatment and Medication for more detail.

Background

Shigellosis occurs when Shigella species invade the epithelial lining of the gastrointestinal tract, causing diarrhea and bacillary dysentery that ranges from mild to severe disease. It is a major public health problem in developing countries where sanitation is poor but also exists in industrialized nations among the homeless and those with low and middle income.[1]

Shigellosis is highly infectious and spreads by fecal-oral transmission. Shigella sonnei and Shigella flexneri cause 90% of the cases of shigellosis; Shigella dysenteriae has produced epidemic shigellosis. Left untreated, fulminant dysentery may occur and is potentially fatal. No vaccine against Shigella species exists yet, however, several are under development.[4, 5, 6, 7]

Pathophysiology

Shigella organisms cause bacillary dysentery,[8, 9, 10] a disease that has been described since early recorded history.

Shigella species (eg, S dysenteriae, S flexneri, S sonnei, S boydii) are aerobic, nonmotile, glucose-fermenting, gram-negative rods that are highly contagious,[9, 11] causing diarrhea after ingestion of as few as 180 organisms.[12]

These pathogens cause damage by two mechanisms, (1) invasion of the colonic epithelium, which is dependent on a plasmid-mediated virulence factor,[8, 9, 10] and (2) production of an enterotoxin, which is not essential for colitis but enhances the virulence.

Lapaquette et al indicate that S flexneri uses a calcium/calpain-dependent mechanism to cause sumoylation inhibition, thereby allowing pathogenic bacterial entry.[13]  

The organism is spread by fecal-oral contact via infected food or water, during travel, or in long-term care facilities, daycare centers, or nursing homes.[14]

Epidemiology

United States data

Shigellosis is the third most common cause of bacterial gastroenteritis in the United States.[15] Approximately 500,000 cases of shigellosis are estimated to occur annually in the United States,[3]  accounting for 100,000 hospitalizations and 500 deaths every year.

S sonnei is the most common species found in the United States and other developed nations. S boydii and S dysenteriae are rare but can be deadly. Most US cases of shigellosis occur in international travelers returning from areas that are prevalent in shigellosis. Relatively recent studies have evaluated an increasing incidence in men who have sex with men (MSM) with local spread of the bacteria.[16, 17]

International data

Shigellosis occurs worldwide, and it tends to occur whenever war, natural calamities (eg, earthquakes, floods), or unhygienic living conditions result in overcrowding and poor sanitation. Recent evidence indicates that rising temperatures also significantly increase the risk of infectious diarrheal diseases, such as shigellosis.[18]  Globally, S sonnei is the second most common infectious species of shigellosis in low- and middle-income countries.[19]  S boydii and S dysenteriae occur more commonly internationally. Worldwide, disease from Shigella species causes an estimated 700,000 deaths and 165 million cases of diarrhea annually.[20] It is not only the global leading pathogen to cause childhood diarrhea but also the predominant pathogen to cause moderate to severe diarrhea in children younger than 5 years.[21]

Race-, sex-, and age-related demographics

No racial or sexual differences exist in Shigella infections. However, reactive arthritis, which is a triad of arthritis, urethritis, and conjunctivitis, occurs most commonly in men aged 20-40 years, and it occurs 2-4 weeks after infection with the Shigella species. Reactive arthritis is associated with the human leukocyte antigen (HLA)–B27 phenotype. The arthritis is asymmetric and can be chronic and relapsing.

Shigellosis is most common in children aged 6 months to 5 years.[4, 20]

Prognosis

Postinfection carriage of shigellosis is generally less than 3-4 weeks. Mild cramps and diarrhea may continue for many days to weeks after treatment of the condition.

Morbidity/mortality

Infection with Shigella species may be associated with extragastrointestinal complications.

  • Bacteremia occurs primarily in malnourished children and carries a mortality of 20% as a result of renal failure, hemolysis, thrombocytopenia, gastrointestinal hemorrhage, and shock.[22, 23]

  • Hemolytic uremic syndrome (HUS) may complicate infections with Shigella species and Escherichia coli, and it carries a mortality of over 50%.[12] HUS is characterized by acute hemolysis, renal failure, uremia, and disseminated intravascular coagulation (DIC).

  • Metabolic disturbances: Hyponatremia secondary to the syndrome of inappropriate antidiuretic hormone (SIADH) secretion may occur.

  • Leukemoid reaction: An elevated white blood cell (WBC) count of 50,000/mm3 occurs in approximately 4% of patients, mainly in children aged 2-10 years.

  • Neurologic disease: Seizures, the most common neurologic complication, are always associated with fever and are generalized. They are typically nonrecurring and uncomplicated. Seizures are least common with S dysenteriae. The prevalence of seizures is approximately 10% across all ages.

  • Encephalopathy with lethargy, confusion, and headache has been noted in up to 40% of children hospitalized with Shigella infections.

  • Reactive arthritis (also known as Reiter syndrome) may occur.

Complications

Complications from shigellosis may be intestinal or systemic.

Intestinal complications

Proctitis or rectal prolapse is common in infants and young children. This is induced by invasion of the organism into the colonic mucosa, causing severe inflammation of the rectum and distal colon.[23, 24]

Toxic megacolon occurs primarily in the setting of S dysenteriae infection. The pathogenesis is unclear, but it occurs in patients with pancolitis and seems to be related to the intensity of the inflammation rather than being mediated by the Shiga toxin.[23, 24]

Intestinal obstruction can develop from severe colonic disease. The incidence of this complication in a series of 1211 patients with shigellosis was 2.5%.[25] The patients with obstruction were more likely to be infected with type 1 S dysenteriae.

Colonic perforation is an extremely rare complication of shigellosis. It occurs primarily in infants or severely malnourished patients and is associated with infection due to type 1 S dysenteriae or S flexneri.[26]

Systemic complications

Shigella bacteremia has a reported incidence of 0-7%. Signs that correlate with bacteremia are leukocytosis, hypothermia, temperature above 39.5ºC, severe dehydration, and lethargy. Bacteremia is more common among children than in adults, occurring primarily in those younger than 5 years.[27, 28] In one study, among the 22 cases of bacteremia described in adults, one third of patients were older than 65 years, and more than half had an underlying disease (most commonly diabetes).[29] However, infection with human immunodeficiency virus (HIV) does not appear to confer a significant predisposition to Shigella bacteremia.

Bacteremia is associated with an increased risk of death.[28] Young malnourished children are at greatest risk. Additionally, the mortality associated with Shigella bacteremia may be higher in the setting of HIV infection.[30] Antibiotic therapy is recommended in all patients who become bacteremic with Shigella.

Metabolic disturbances may occur. Substantial volume depletion is uncommon in shigellosis, because the stool volume is usually very low. In one study, hyponatremia, defined as serum sodium levels below 120 mEq/L, was noted in 29% of patients hospitalized with diarrhea due to type 1 S dysenteriae.[31] However, the hyponatremia is generally caused by SIADH secretion, not volume depletion. Protein-losing enteropathy may also be observed. Increased catabolism secondary to fever, stool protein loss, decreased intake owing to anorexia, and malabsorption can exacerbate preexisting malnutrition.

Leukemoid reaction, defined as an WBC count of 50,000/mm3 or more, has been observed in Bangladesh in approximately 4% of patients, most commonly in children between the ages of 2 and 10 years. In contrast, a study conducted in the United States found no association between disease severity and an elevated WBC count.[32]

Neurologic complications associated with Shigella infection may arise, of which seizures are the most common. These tend to be generalized seizures. Although they are not associated with specific neurologic deficits, they have been associated with a higher risk of death. Seizures occur almost exclusively among children younger than 15 years. The occurrence of seizures has been observed during infection with all serotypes of Shigella, and they are associated with fever (often >39ºC), an increased proportion of immature leukocytes, low serum sodium levels, and high serum potassium levels. Analysis of cerebrospinal fluid (CSF) obtained by lumbar puncture is typically normal, although up to 15% may demonstrate mild lymphocytic pleocytosis with up to 12 cells.[33]

In addition to seizures, other neurologic findings have been described in up to 40% of children hospitalized with Shigella infection, including encephalopathy with lethargy, confusion, and headache.[34] Obtundation, coma, and posturing are rare. In cases of fatal encephalopathy, cerebral edema has been observed at autopsy.

A particularly lethal form of shigellosis, known as Ekiri syndrome associated with S sonnei infection, was responsible for 15,000 deaths per year in Japan during the pre-World War II era. Ekiri syndrome was characterized by the rapid development of seizures and coma in patients with high fever and few dysenteric symptoms. The mechanism of the fulminant course of this disease remains unclear.[23]

Reactive arthritis is an uncommon complication that may follow S flexneri infection. It is a sterile inflammatory arthritis that can occur alone or in association with conjunctivitis and urethritis. Symptoms develop 1-2 weeks following symptoms of dysentery, regardless of whether or not the dysentery was treated with antibiotics. Approximately 70% of patients with post-shigellosis reactive arthritis are HLA-B27 positive.[35]

HUS is a relatively uncommon disease; however, it is the most frequent cause of acute renal failure among infants and young children worldwide. About 90% of cases of pediatric HUS follow a diarrheal prodrome that is most commonly due to infection with enterohemorrhagic E coli (particularly type O157:H7) but that may also be induced by infection with type 1 S dysenteriae.[23, 36]

At the end of the first week and during the recovery phase of diarrheal or dysenteric symptoms, patients with HUS present with a combination of microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure (initially oliguric and then anuric). These patients may be considered to have thrombotic thrombocytopenic purpura (TTP) if fever and transient neurologic symptoms are also present. Seizures occur in approximately 10% of affected patients, and stroke or cerebral edema occur in 5%.

The pathogenesis of HUS or TTP involves cytotoxic damage to the vascular endothelium. In most studies, Shiga toxin production by type 1 S dysenteriae is thought to be directly involved.

Other manifestations can also occur. In young girls, Shigella can cause vaginitis or vulvovaginitis, with or without diarrhea.[37] Rarely, keratitis or conjunctivitis and acute myocarditis may develop.[38, 39]

Patient Education

Educate patients about proper hygiene. Careful handwashing and stool precautions should prevent the dissemination of shigellosis. Thus, primary preventive measures should include universal availability of potable water, provision of sanitation methods, and improved personal and food hygiene.[4]

 

Presentation

History and Physical Examination

History

Manifestations of shigellosis generally begin within 1-2 days of infection and can include a range of the following signs and symptoms[1, 3] :

  • Acute bloody diarrhea[40]

  • Crampy abdominal pain

  • Tenesmus

  • Urgency

  • Fever (1-3 days after exposure)

  • Occasional vomiting (35% prevalence)

  • Dehydration

These symptoms are usually self-limiting and can last from 2 to 7 days. However, certain populations are at an increased risk of severe shigellosis infection, including children in daycare, incarcerated persons, international travelers,[41] men who have sex with men,[41] people infected with human immunodeficiency virus (HIV), and those who live in crowded, unsanitary conditions.

Physical examination

Clinical findings may include the following:

  • Lower abdominal tenderness

  • Normal or increased bowel sounds

  • Dehydration (occasional)

 

DDx

 

Workup

Approach Considerations

Stool culture should be obtained in all suspected cases of shigellosis. Specimens should be processed immediately after collection. Ova and parasite stool studies should be collected to rule out other causes of infectious diarrhea such as Entamoeba histolytica and parasitic worms.

Other laboratory tests, such as a white blood cell (WBC) count, may be performed in persons with severe symptoms or to rule out other causes. Creatinine and blood urea nitrogen (BUN) should be monitored to assess the hydration status of the patient.

Laboratory studies generally reveal the following findings:

  • Fecal leukocytes and erythrocytes

  • Mildly elevated hematocrit, sodium, and urea nitrogen levels: These are indicative of volume depletion in cases of shigellosis.

  • Leukocytosis: Rare.

  • Positive findings on stool culture of a fresh fecal specimen

  • Immunocompromised patients (eg, infected with human immunodeficiency virus [HIV]): Blood cultures are rarely helpful in cases of shigellosis.

Procedures

Sigmoidoscopy

Sigmoidoscopy is not necessary in most cases of shigellosis.

Colonic biopsy

If distinguishing between dysentery and the acute presentation of idiopathic ulcerative colitis is urgently necessary, a colonic biopsy may be useful if it is performed within 4 days of the onset of symptoms.

In general, histologic findings of shigellosis include the following:

  • Intense neutrophilic and mononuclear cells infiltrating the lamina propria

  • Hemorrhage

  • Ulcers

  • Mucous depletion

  • Occasional crypt abscesses

 

Treatment

Approach Considerations

Maintain hydration in patients with shigellosis to compensate for fluid losses from diarrhea.

Antibiotic treatment is indicated in most patients with a positive stool culture for Shigella. Treatment can reduce symptoms by 2 days.

Indications for treatment per Centers for Disease Control and Prevention (CDC) recommendations include persons who work in public setting (ie, food handlers, childcare providers, residents of nursing homes), have a immunocompromised state (including individuals with human immunodeficiency virus [HIV] infection), and patients with severe disease (those who require hospitalization or have complications). Patients infected with Shigella may shed the bacteria for up to 6 weeks, even after resolution of symptoms.[3]

Avoid the use of antimotility agents, because they have the potential to worsen the symptoms and may predispose to toxic dilatation of the colon.

Clear liquids followed by a low residue, lactose-free diet are recommended until symptoms of shigellosis resolve.

Medical Care

General supportive care of patients with shigellosis includes the following[42] :

  • Treat high fever in children.

  • Avoid narcotic-related antidiarrheals.

  • Antibiotic treatment is indicated in most patients.[43] Note that antibiotic-resistant Shigella species have emerged[19, 20] ; thus, obtaining susceptibility testing and monitoring local shigellosis outbreaks is crucial.

  • Clear liquids followed by a low-residue, lactose-free diet is recommended until symptoms of shigellosis resolve.

As noted earlier, antimotility agents should be avoided, as they have the potential to worsen symptoms and may predispose to toxic dilatation of the colon.

For fluid and electrolyte supplementation, oral rehydration solutions are preferable.

Consultations

Consult a gastroenterologist or an infectious diseases expert if the Shigella infection is prolonged or if the patient experiences a severe course of shigellosis that is unresponsive to antibiotics.

Prevention

A vaccine for shigellosis is not currently available. Until a vaccine is available, the following measures can help prevent the dissemination of shigellosis:

  • Use of safe drinking water

  • Chlorination of unreliable water sources

  • Strict handwashing

  • Refrigeration and proper preparation and cooking of food. Food handlers must be treated with antibiotics and should not be involved in food preparation as long as stool cultures are positive for Shigella infection. At least 48 hours of antibiotic treatment are usually required.

 

Medication

Medication Summary

Shigella infection produces a self-limited diarrheal illness that lasts 5-7 days and may not require antibiotics in individuals who are otherwise healthy.[3] However, for public health reasons, most experts recommend treating any person whose stool culture is positive for Shigella species. Moreover, antibiotics have been shown to decrease the duration of fever and diarrhea by about 2 days. The shorter duration of shedding with antibiotic therapy can reduce the risk of person-to-person spread. Antibiotic treatment is definitely recommended for infirm or older patients, malnourished children, patients infected with human immunodeficiency virus (HIV), food handlers, healthcare workers, and children in daycare centers.[43] However, antibiotic-resistant strains of Shigella have emerged, posing therapeutic challenges.[20, 44]

Ampicillin was widely used in the past but is no longer an effective empiric treatment in the United States because of antibiotic resistance.[45] In fact, antibiotic resistance to Shigella species is widespread and increasing worldwide. Thus, antibiotic susceptibility testing is essential for the management of patients with suspected Shigella infection.

At present, ciprofloxacin, azithromycin, and ceftriaxone are the mainstays of treatment for shigellosis. However,  increasing evidence exists in some regions of decreased susceptibility or full resistance to these agents.[5, 46, 47]

In a study comprising 90 patients with shigellosis from 2008 to 2013 who had acquired Shigella as traveler's diarrhea or domestically acquired diarrhea, Toro et al detected the highest resistance for trimethoprim/sulfamethoxazole (81.8%), followed by ampicillin (37.8%) and ciprofloxacin (23.3%).[48]

In 2012, there was a S sonnei outbreak in Los Angeles, California. Isolates submitted to the Centers for Disease Control and Prevention (CDC) revealed elevated azithromycin minimum inhibitory concentration (MIC) of more than 16 μg/mL.[2]

Given the widespread resistance to ciprofloxacin as well as trimethoprim-sulfamethoxazole and azithromycin, a third-generation cephalosporin is appropriate empiric therapy in the setting of acute illness.[43, 49] The treatment of choice for HIV-infected patients is a quinolone for 5 days.

Antibiotics

Class Summary

Empiric antimicrobial therapy must be comprehensive and should cover all likely pathogens in the context of the clinical setting.[50, 51]

Ceftriaxone (Rocephin)

Third-generation cephalosporin with broad-spectrum, gram-negative activity; lower efficacy against gram-positive organisms; higher efficacy against resistant organisms. Bactericidal activity results from inhibiting cell wall synthesis by binding to one or more penicillin binding proteins. Exerts antimicrobial effect by interfering with the synthesis of peptidoglycan, a major structural component of bacterial cell wall. Bacteria eventually lyse due to the ongoing activity of cell wall autolytic enzymes while cell wall assembly is arrested.

Highly stable in the presence of beta-lactamases, both penicillinase and cephalosporinase, of gram-negative and gram-positive bacteria. Approximately 33-67% of the dose is excreted unchanged in urine, and the remainder is secreted in bile and ultimately in feces as microbiologically inactive compounds. Reversibly binds to human plasma proteins, and binding have been reported to decrease from 95% bound at plasma concentrations <25 mcg/mL to 85% bound at 300 mcg/mL.

Ciprofloxacin (Cipro)

Fluoroquinolone that inhibits bacterial DNA synthesis and, consequently, bacterial growth.

Trimethoprim-sulfamethoxazole (Bactrim, Septra, Bactrim DS, Cotrim)

Inhibits bacterial growth by inhibiting synthesis of dihydrofolic acid. Reasonable drug of choice (DOC) in the United States due to few resistant strains.

Dosing may be based on TMP component.

Azithromycin (Zithromax)

Acts by binding to 50S ribosomal subunit of susceptible microorganisms and blocks the dissociation of peptidyl tRNA from ribosomes, causing the arrest of RNA-dependent protein synthesis. Nucleic acid synthesis is not affected.

Concentrates in phagocytes and fibroblasts as demonstrated by in vitro incubation techniques. In vivo studies suggest that the concentration in phagocytes may contribute to drug distribution in inflamed tissues.

Treats mild-to-moderate microbial infections.

Plasma concentrations are very low, but tissue concentrations are much higher, giving it value in treating intracellular organisms. Has a long tissue half-life.

 

Questions & Answers