The condition depicted is human intestinal spirochetosis (Figure; ×1000, oil immersion). It is characterized by fringelike, end-on attachment of densely packed spirochetes to the epithelial surface of the large intestines.1 In humans, the culprit bacteria are commonly Brachyspira aalborgi and Brachyspira pilosicoli. The spirochetes may invade beyond the surface epithelium. Individuals colonized by the bacteria may be asymptomatic or symptomatic. The condition is common in homosexual men and in men positive for human immunodeficiency virus, who are likely to be symptomatic irrespective of invasion.2 Symptomatic individuals may be effectively treated with metronidazole. Steiner, Warthin-Starry, and periodic acid–Schiff are some of the special stains that can be used to highlight the organism. Fluorescence in situ hybridization and electron microscopy are also used to confirm the identity of the bacteria. Our patient is a 55-year-old, human immunodeficiency virus–positive man who presented with diarrhea.

Jensen
,
T. K.
,
M.
Boye
, and
P.
Ahrens
.
et al
.
Diagnostic examination of human intestinal spirochetosis by fluorescence in situ hybridization for Brachyspira aalborgi, Brachyspira pilosicoli, and other species of the genus Brachyspira (Serpulina).
J Clin Microbiol
2001
.
39
:
4111
4118
.
Korner
,
M.
and
J. O.
Gebbers
.
Clinical significance of human intestinal spirochetosis: a morphologic approach.
Infection
2003
.
5
:
341
349
.

The authors have no relevant financial interest in the products or companies described in this article.

Author notes

Reprints: Grace Guzman, MD, Department of Pathology, Division of Surgical Pathology, University of Illinois Medical Center at Chicago, 1819 W Polk St, Room 446, m/c 847, Chicago, IL 60612 ([email protected])