Amebiasis, Emergency Medicine

Basics

Description

Invasive parasitic infection with both intestinal and extraintestinal manifestations
Endemic worldwide, especially areas with poor sanitation
Populations at risk:
- Travelers to, citizens of, and immigrants from endemic areas
- Institutionalized persons
- Practitioners of oral-anal sexual activity
- Men who have sex with men (MSM)
- HIV infected individuals
Risk factors for increased severity of disease and complications:
- Immunocompromised: Corticosteroid use, HIV infection, malnutrition, malignancy
- Pregnancy/postpartum state
- Extremes of age

Etiology

Entamoeba histolytica, an anaerobic, nonflagellated protozoa
Fecal-oral transmission:
- Humans are sole reservoir.
Ingested organisms cause invasive colitis.
Extraintestinal spread is hematogenous.

Diagnosis

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:
  - Bloody mucoid diarrhea
  - Abdominal pain/benign abdominal exam
  - Tenesmus
  - Weight loss
  - Fever (rare)
- 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

Fulminant colitis is more likely
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:
- Leukocytosis in amebic liver abscess and peritonitis
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:
- Suspect amebic brain abscess if patient with known amebiasis has altered mental status or focal neurologic findings.
- Irregular nonenhancing lesions
CXR:
- Elevated right hemidiaphragm and/or right pleural effusion in liver abscess

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:
- Enteroinvasive bacterial infection (Staphylococcus, E. coli, Shigella, Salmonella, Yersinia, Campylobacter)
- Inflammatory bowel disease
- Ischemic colitis
- Arteriovenous malformation
- Abdominal aortic aneurysm
- Perforated duodenal ulcer
- Intussusception, diverticulitis
- Pancreatitis
- Colorectal carcinoma
Amebic abscess:
- Bacterial abscess
- Tuberculous cavity
- Echinococcal cyst
- Malignancy
- Cholecystitis
Cutaneous amebiasis:
- Carcinoma
- STDs (condyloma acuminata, chancroid, syphilis)

Treatment

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.

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

Chloroquine and iodoquinol are contraindicated.
Tetracycline contraindicated in children <8 yr

Use erythromycin or nitazoxanide only.

Follow-Up

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.

Pearls and Pitfalls

Avoid antidiarrheal medications
Always give double therapy with both a systemic amebicidal (metronidazole, tinidazole, or chloroquine) plus an intestinal amebicidal (erythromycin, iodoquinol, nitazoxanide, paromomycin, or tetracycline) unless contraindicated.
Always be vigilant for high-mortality complications such as fulminant colitis or extraintestinal disease.

Additional Reading

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.

Codes

ICD9

006.0 Acute amebic dysentery without mention of abscess
006.1 Chronic intestinal amebiasis without mention of abscess
006.9 Amebiasis, unspecified
006.8 Amebic infection of other sites
006.2 Amebic nondysenteric colitis
006.3 Amebic liver abscess
006.4 Amebic lung abscess
006.5 Amebic brain abscess
006.6 Amebic skin ulceration
006 Amebiasis

ICD10

A06.0 Acute amebic dysentery
A06.1 Chronic intestinal amebiasis
A06.9 Amebiasis, unspecified
A06.89 Other amebic infections
A06.2 Amebic nondysenteric colitis
A06.3 Ameboma of intestine
A06.4 Amebic liver abscess
A06.5 Amebic lung abscess
A06.6 Amebic brain abscess
A06.7 Cutaneous amebiasis
A06.81 Amebic cystitis
A06.82 Other amebic genitourinary infections
A06.8 Amebic infection of other sites
A06 Amebiasis

SNOMED

111910009 Amebic infection (disorder)
186116005 Acute amebic dysentery (disorder)
23874000 Chronic amebiasis (disorder)
238449000 Amebiasis of skin (disorder)
406559005 Amebic infection of central nervous system
65095005 Amebic lung abscess
75119003 Amebic liver abscess (disorder)

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