Shigella: Difference between revisions
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Shigella
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==Background== |
==Background== |
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*[[Stain::Gram-negative]] [[Shape::bacillus]] |
*[[Stain::Gram-negative]] [[Shape::bacillus]] within the family [[Family::Enterobacteriaceae]] and order [[Order::Enterobacterales]] |
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**Most closely related to [[Escherichia coli]] |
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*Species include [[Shigella dysenteriae]], [[Shigella sonnei]], [[Shigella flexneri]], and [[Shigella boydii]] |
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**At least 40 serotypes |
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*Strains that encode Shiga toxin include [[Shigella dysenteriae]] serotype 1 (most common), [[Shigella flexneri]] type 2a, [[Shigella dysenteriae]] type 4, and [[Shigella sonnei]] |
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*Automated methods frequently misidentify as [[Escherichia coli]], so needs phenotypic testing with serology |
*Automated methods frequently misidentify as [[Escherichia coli]], so needs phenotypic testing with serology |
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*Needs azithromycin susceptibility to be requested specifically, if it is resistant to others |
*Needs [[azithromycin]] susceptibility to be requested specifically, if it is resistant to others |
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**However, there are no standardized breakpoints, so you have to use the epidemiologic cutoff values |
**However, there are no standardized breakpoints, so you have to use the epidemiologic cutoff values |
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*Extensively drug resistant (XDR) Shigella is resistant to [[ampicillin]], [[fluoroquinolones]], [[third-generation cephalosporins]], [[azithromycin]], and [[co-trimoxazole]] |
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==Clinical Manifestations== |
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* Most commonly causes self-limited diarrheal illness with watery or loose stools |
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* Disease may be more severe, including high fever, abdominal cramps, abdominal tenderness, tenesmus, mucoid stools, and [[hematochezia]] |
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* Complications of severe disease include [[bacteremia]], [[pseudomembranous colitis]], [[toxic megacolon]], [[intestinal perforation]], [[hemolysis]], and [[hemolytic-uremic syndrome]] |
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** Bacteremia more common in neonates and patients with malnutrition |
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* Serotype 1 is more likely to cause severe illness |
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== Diagnosis == |
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* Molecular testing with PCR of stool is the most common method of diagnosing diarrheal illness |
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* Culture of stool or rectal swab |
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** Mass spectrometry cannot reliably differentiate from [[Escherichia coli]], so needs biochemical identification |
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== Management == |
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* Supportive care and oral rehydration |
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* Avoid antidiarrheal or antimotility agents, which can prolong the clinical course and increase risk of severe disease |
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* If severe disease or immunocompromised, should be treated empirically with antimicrobials |
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** Ideally should be directed by susceptibility data |
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** [[Azithromycin]] for 3 days or [[ceftriaxone]] for 2 to 5 days are good empiric options, though resistance is increasing |
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** Other options include [[ciprofloxacin]] for 3 days, [[ampicillin]] for 5 days, or [[trimethoprim-sulfamethoxazole]] for 5 days |
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*** Avoid [[fluoroquinolones]] if MIC ≥0.12 μg/mL |
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*** Avoid [[amoxicillin]], which may not be well-absorbed |
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[[Category:Gram-negative bacilli]] |
[[Category:Gram-negative bacilli]] |
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[[Category:Gastrointestinal infections]] |
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Latest revision as of 20:33, 5 May 2023
Background
- Gram-negative bacillus within the family Enterobacteriaceae and order Enterobacterales
- Most closely related to Escherichia coli
- Species include Shigella dysenteriae, Shigella sonnei, Shigella flexneri, and Shigella boydii
- At least 40 serotypes
- Strains that encode Shiga toxin include Shigella dysenteriae serotype 1 (most common), Shigella flexneri type 2a, Shigella dysenteriae type 4, and Shigella sonnei
- Automated methods frequently misidentify as Escherichia coli, so needs phenotypic testing with serology
- Needs azithromycin susceptibility to be requested specifically, if it is resistant to others
- However, there are no standardized breakpoints, so you have to use the epidemiologic cutoff values
- Extensively drug resistant (XDR) Shigella is resistant to ampicillin, fluoroquinolones, third-generation cephalosporins, azithromycin, and co-trimoxazole
Clinical Manifestations
- Most commonly causes self-limited diarrheal illness with watery or loose stools
- Disease may be more severe, including high fever, abdominal cramps, abdominal tenderness, tenesmus, mucoid stools, and hematochezia
- Complications of severe disease include bacteremia, pseudomembranous colitis, toxic megacolon, intestinal perforation, hemolysis, and hemolytic-uremic syndrome
- Bacteremia more common in neonates and patients with malnutrition
- Serotype 1 is more likely to cause severe illness
Post-Infectious Complications
Diagnosis
- Molecular testing with PCR of stool is the most common method of diagnosing diarrheal illness
- Culture of stool or rectal swab
- Mass spectrometry cannot reliably differentiate from Escherichia coli, so needs biochemical identification
Management
- Supportive care and oral rehydration
- Avoid antidiarrheal or antimotility agents, which can prolong the clinical course and increase risk of severe disease
- If severe disease or immunocompromised, should be treated empirically with antimicrobials
- Ideally should be directed by susceptibility data
- Azithromycin for 3 days or ceftriaxone for 2 to 5 days are good empiric options, though resistance is increasing
- Other options include ciprofloxacin for 3 days, ampicillin for 5 days, or trimethoprim-sulfamethoxazole for 5 days
- Avoid fluoroquinolones if MIC ≥0.12 μg/mL
- Avoid amoxicillin, which may not be well-absorbed
