SIGNS AND SYMPTOMS 
- Intestinal disease:
- Onset 1 wk to 1 mo postexposure
- Acute diarrhea (nondysenteric colitis):
- 80% of cases
- Afebrile
- Occult blood in stool
- Benign abdominal exam
- Classic dysentery:
- Fulminant colitis:
- Toxic-appearing patient
- Rigid abdomen (25%)
- Fever
- Severe bloody diarrhea
- Rapid progression to perforated bowel and frank peritonitis
- > 40% mortality
- Toxic megacolon:
- Toxic-appearing patient
- Profuse diarrhea (> 10 stools per day)
- Fever
- Distended, tympanitic abdomen with signs of peritonitis
- Associated with corticosteroid use
- High mortality
- Ameboma:
- Intraluminal granulated mass
- Tender palpable mass on exam
- Amebic strictures:
- Owing to chronic inflammation/scarring
- Crampy abdominal pain
- Nausea and vomiting (may be feculent)
- Partial or complete bowel obstruction
- Chronic amebic colitis:
- Mild recurrent episodes of bloody diarrhea, abdominal cramping, and tenesmus
- Weight loss
- May persist for years
- Extraintestinal disease:
- Amebic liver abscess:
- Most frequent extraintestinal manifestation (3–9% of cases)
- Single abscess in right lobe (50–80%)
- May develop months to years postexposure (median of 3 mo)
- Fever
- Right upper quadrant pain
- Hepatomegaly with point tenderness
- Rales at right lung base
- Concurrent diarrhea unusual (20–33%)
- Complication: Rupture into pleural cavity (10–20%), peritoneum, or pericardium (rare)
- Increased risk of rupture if > 5 cm in diameter or left lobe location
- Extrahepatic amebic abscess:
- Brain
- Lung
- Perinephric
- Splenic
- Vaginal/cervical/uterine
- Cutaneous amebiasis:
- Perineum and genitalia
- Painful, irregularly shaped ulcers
- Purulent exudate
Pediatric Considerations
Fulminant colitis is more likely
Pregnancy Considerations
Fulminant colitis is more likely
History
- Possible sources of exposure
- Membership in high-risk group
Physical Exam
- Identify evidence of peritonitis, sepsis, or shock.
- Tender abdominal mass mandates workup for liver abscess or ameboma.
- Digital rectal exam shows gross or occult blood in > 70% of patients.
DIAGNOSIS TESTS & INTERPRETATION
Lab
- CBC:
- Alkaline phosphatase and ALT:
- Elevated in amebic liver abscess
- Serum electrolytes, BUN/creatinine if prolonged diarrhea or evidence of dehydration
- Stool PCR is diagnostic gold standard:
- 100% sensitive and specific
- Stool ELISA for E. histolytica–specific antigen:
- 74–95% sensitive, 93–100% specific
- Serum for anti-E. histolytica antibodies:
- Essential if suspecting liver abscess. These patients rarely shed parasites in stool
- 90–100% sensitive in amebic liver abscess
- 70–90% sensitive in amebic colitis
- Stool microscopy is < 60% sensitive and no longer the test of choice.
- Fecal leukocytes and culture:
- Rule out infection of enteroinvasive bacteria;
- Negative in amebiasis
Imaging
- Abdominal US:
- 58–90% sensitive for liver abscess
- Sensitivity influenced by size and location
- Evaluate abscess for increased risk of rupture (> 5 cm or located in left lobe)
- Abdominal CT or MRI:
- Equivalent to US for delineating liver abscesses
- Superior to US for detecting abscesses in other organs
- Head CT or MRI:
- CXR:
Diagnostic Procedures/Surgery
- Colonoscopy with biopsy provides definitive diagnosis of amebic dysentery, colitis, ameboma, and amebic stricture.
- Percutaneous fine-needle aspiration of liver abscess to exclude bacterial abscess if nondiagnostic serology or antiamebic therapy fails
- Not for primary treatment of liver abscesses
DIFFERENTIAL DIAGNOSIS
- Intestinal amebiasis:
- Amebic abscess:
- Bacterial abscess
- Tuberculous cavity
- Echinococcal cyst
- Malignancy
- Cholecystitis
- Cutaneous amebiasis:
[Outline]
INITIAL STABILIZATION/THERAPY
- Airway, breathing, circulation (ABCs)
- IV 0.9% NS if signs of significant shock
ED TREATMENT/PROCEDURES
- Oral fluids if mild; IV if moderate/severe dehydration
- Avoid antidiarrheal agents.
- Correct serum electrolyte imbalances.
- Stool sample for E. histolytica PCR or ELISA, plus serology for anti–E. histolytica antibodies
- If stool or serum is positive for E. histolytica:
- Metronidazole or tinidazole is 1st-line drug for systemic amebiasis (90% cure rate)
- Chloroquine is an alternative systemic agent
- Always follow systemic therapy with a luminal agent to eradicate intestinal colonization (erythromycin, iodoquinol, nitazoxanide, paromomycin, or tetracycline).
- Do not use the luminal agents alone
- If stool or serum is negative for E. histolytica:
- Refer to gastroenterologist for colonoscopy with biopsy.
- Repeat serology in 7 days.
- Consider empiric course of metronidazole if high suspicion for amebiasis and patient is critically ill.
- If evidence of peritonitis or sepsis:
- Add IV antibiotic directed against anaerobic and gram-negative bacteria.
- Surgery if toxic megacolon or perforation
- If liver abscess is suspected:
- US or CT of hepatobiliary system with concurrent amebic serology
- If imaging demonstrates an abscess but serology is negative, treat with amebicides and repeat serology in 7 days.
- Consider abscess drainage by surgeon or interventional radiologist in conjunction with amebicidal therapy.
- If symptoms do not improve after 5–7 days of empiric amebicidal therapy, consider fine-needle aspiration to rule out bacterial abscess or hepatoma.
Pregnancy Considerations
- Use metronidazole with caution in 1st-trimester pregnancy, but do not withhold if patient has fulminant colitis or amebic abscess.
- Use erythromycin or nitazoxanide as intestinal amebicides along with metronidazole.
- Erythromycin or nitazoxanide may be used alone for mild dysentery in 1st-trimester pregnancy.
- Chloroquine, iodoquinol, paromomycin, tetracycline, and tinidazole are contraindicated.
MEDICATION
First Line
- Metronidazole: 500–750 mg (peds: 30–50 mg/kg/24 h) PO/IV q8h for 5–10 d
- Tinidazole: 2 g/d (peds: 50–60 mg/kg/d) PO for 3–6 d. For children older than 3 yr
Second Line
- Chloroquine: 1,000 mg/d PO for 2 d then 500 mg/d PO for 14 d; or 200 mg IM for 10–12 d
- Erythromycin: 250–500 mg (peds: 30–50 mg/kg/24 h) PO q6h for 10–14 d
- Iodoquinol: 650 mg PO q8h for 20 d
- Nitazoxanide: 500 mg PO q12. for 3 d (10 d if liver abscess) for children > 12 yr
- Paromomycin: 500 mg (peds: 25–30 mg/kg/24 h) PO q8h for 5–10 d
- Tetracycline: 250–500 mg (peds[> 12 yr]: 25–50 mg/kg/24 h) PO q6h for 10 d
Pediatric Considerations
- Chloroquine and iodoquinol are contraindicated.
- Tetracycline contraindicated in children < 8 yr
Pregnancy Considerations
Use erythromycin or nitazoxanide only.
[Outline]
DISPOSITION
Admission Criteria
- Shock, sepsis, or peritonitis
- Hypotension or tachycardia unresponsive to IV fluids
- Children with > 10% dehydration
- Severe electrolyte imbalance
- Patients unable to maintain adequate oral hydration:
- Extremes of age, cognitive impairment, significant comorbid illness
- Fulminant colitis or toxic megacolon
- Bowel obstruction
- Extraintestinal abscesses
- Failure of outpatient regimen
Discharge Criteria
- Nontoxic presentation of acute or chronic dysentery
- Able to maintain adequate oral hydration and medication compliance
- Dehydration responsive to IV fluids
Issues for Referral
Consult surgery if evidence of peritonitis, toxic megacolon, colonic perforation, or liver abscess.
FOLLOW-UP RECOMMENDATIONS
- Gastroenterology and infectious disease follow-up in 7 days for repeat serology and possible endoscopic evaluation.
- Physical exam in 14 days to assess for treatment effectiveness and for development of complications or extraintestinal disease.
[Outline]
- Chavez-Tapia NC, Hernandez-Calleros J, Tellez-Avila FI, et al. Image-guided percutaneous procedure plus metronidazole versus metronidazole alone for uncomplicated amoebic liver abscess. Cochrane Database Syst Rev. 2009;1:CD004886. doi:10.1002/14651858.CD004886.pub2.
- Escobedo AA, Almirall P, Alfonso M, et al. Treatment of intestinal protozoan infections in children. Arch Dis Child. 2009;94:478–482.
- Fotedar R, Stark D, Beebe N, et al. Laboratory diagnostic techniques for Entamoeba species. Clin Microbiol Rev. 2007;20:511–532.
- Gonzalez MLM, Dans LF, Martinez EG. Antiamoebic drugs for treating amoebic colitis. Cochrane Database Syst Rev. 2009;2:CD006085. doi:10.1002/14651858.CD006085.pub2.
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