Underestimated amoebic appendicitis among HIV-1-infected individuals in Japan

Taiichiro Kobayashi, Koji Watanabe, Hideaki Yano, Yukinori Murata, Toru Igari, Kumiko Nakada-Tsukui, Kenji Yagita, Tomoyoshi Nozaki, Mitsuo Kaku, Kunihisa Tsukada, Hiroyuki Gatanaga, Yoshimi Kikuchi, Shinichi Oka

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)


Entamoeba histolytica is not a common causative agent of acute appendicitis. However, amoebic appendicitis can sometimes be severe and life threatening, mainly due to a lack of awareness. Also, its frequency, clinical features, and pathogenesis remain unclear. The study subjects were HIV-1-infected individuals who presented with acute appendicitis and later underwent appendectomy at our hospital between 1996 and 2014. Formalin-fixed paraffin-embedded preserved appendix specimens were reexamined by periodic acid-Schiff (PAS) staining and PCR to identify undiagnosed amoebic appendicitis. Appendectomies were performed in 57 patients with acute appendicitis. The seroprevalence of E. histolytica was 33% (14/43) from the available stored sera. Based on the medical records, only 3 cases were clinically diagnosed as amoebic appendicitis, including 2 diagnosed at the time of appendectomy and 1 case diagnosed by rereview of the appendix after the development of postoperative complications. Retrospective analyses using PAS staining and PCR identified 3 and 3 more cases, respectively. Thus, E. histolytica infection was confirmed in 9 cases (15.8%) in the present study. Apart from a significantly higher leukocyte count in E. histolytica-positive patients than in negative patients (median, 13,760 versus 10,385 cells/μl, respectively, P = 0.02), there were no other differences in the clinical features of the PCR-positive and -negative groups. In conclusion, E. histolytica infection was confirmed in 9 (15.8%) of the appendicitis cases. However, only 3, including one diagnosed after intestinal perforation, were diagnosed before the present analyses. These results strongly suggest there is frequently a failure to detect trophozoites in routine examination, resulting in an underestimation of the incidence of amoebic appendicitis.

Original languageEnglish
Pages (from-to)313-320
Number of pages8
JournalJournal of Clinical Microbiology
Issue number1
Publication statusPublished - 2017 Jan


  • Appendicitis
  • Entamoeba histolytica
  • Japan
  • PCR
  • S-D locus

ASJC Scopus subject areas

  • Microbiology (medical)


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