Shigella species
From IDWiki
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
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
