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Amebiasis (Entamoeba histolytica)
1990 Case Definition

Clinical Description

Infection of the large intestine by Entamoeba histolytica may result in an illness of variable severity ranging from mild, chronic diarrhea to fulminant dysentery. Infection also may be asymptomatic. Extraintestinal infection also can occur (e.g., hepatic abscess).

Laboratory Criteria for Diagnosis

Intestinal amebiasis

  • Demonstration of cysts or trophozoites of E. histolytica in stool, OR
  • Demonstration of trophozoites in tissue biopsy or ulcer scrapings by culture or histopathology
Extraintestinal amebiasis
  • Demonstration of E. histolytica trophozoites in extraintestinal tissue

Case Classification


Confirmed, intestinal amebiasis: a clinically compatible illness that is laboratory confirmed

Confirmed, extraintestinal amebiasis: a parasitologically confirmed infection of extraintestinal tissue, or among symptomatic persons (with clinical or radiographic findings consistent with extraintestinal infection), demonstration of specific antibody against E. histolytica as measured by indirect hemagglutination or other reliable immunodiagnostic test (e.g., enzyme-linked immunosorbent assay)


Asymptomatic intestinal carriage of E. histolytica should not be reported. Among asymptomatic persons, a positive serologic test does not necessarily indicate extraintestinal amebiasis.

The 1990 case definition appearing on this page was re-published in the 1997 MMWR Recommendations and Reports titled Case Definitions for Infectious Conditions Under Public Health Surveillance.1 Thus, the 1990 and 1997 versions of the case definition are identical.


  1. CDC. (1997). Case Definitions for Infectious Conditions Under Public Health Surveillance. MMWR, 46(RR-10), 1-55.