Jpn.J.Infect.Dis., 52, 1999

Laboratory and Epidemiology Communications

Entamoeba histolytica Outbreaks in Institutions for the Mentally Retarded

Niichiro Abe*, Yoshikazu Nishikawa, Akira Yasukawa and Kosuke Haruki

Department of Health and Epidemiology, Osaka City Institute of Public Health and Environmental Sciences, 8-34 Tojo-cho, Tennoji, Osaka 543-0026, Japan

Communicated by Shunsuke Imai

(Accepted July 14, 1999)

We report here an amebiasis outbreak among the residents of two institutions for the mentally retarded in Osaka City. In February 1996, a liver abscess due to Entamoeba histolytica was found in a resident of institution A. In June, several residents in institution B complained diarrhea. Their stools contained E. histolytica.

The stool specimens from the residents, their parents and the staff of the two institutions were examined for Entamoeba. The parasites were first concentrated by the formalin-ether technique (MGL method) (1). The pellet was then suspended in a drop of Lugol's iodine and the wet mounts were examined under a light microscope. The serum E. histolytica-specific antibodies were detected by indirect hemagglutination (Amebiasis HA-Test; Japan Lyophilization Laboratory, Tokyo). The patients who showed positive both in the hemagglutination test and in the stool examination were considered E. histolytica-infected. The stool specimens from individuals who showed negative in the hemagglutination test but positive in the stool examination were further examined using polymerase chain reaction (2) to differentiate E. histolytica from E. dispar. There were 12 such patients and all were found to be E. histolytica-infected. Therefore, all the stool specimens found positive for the parasite were considered E. histolytica-infected.

The results of the examination of the stool specimens for Entamoebae are summarized in Table 1. Thirteen among 79 residents in institution A (16.5%) and 29 among 69 residents in institution B (42.0%) carried E. histolytica cysts. The incidence of E. histolytica in the staff was zero in institution A and one in 41 in institution B. The stools of all the parents were negative for E. histolytica. The risk of infection from the residents to the staff or to their parents appeared very low.

In the serological examination, 15 of 79 residents in institution A and 26 of 69 residents in institution B showed positive for E. histolytica antibodies. Among the seropositives, 12 in institution A and 18 in institution B carried the Entamoeba cysts. Among 71 staff members, only one was seropositive. A total of 30 residents from the both institutions showed clinical symptoms such as diarrhea, abdominal pain, etc. All showed positive for the antibodies and E. histolytica in the stool.

The rate of infection was much higher in institution B than in institution A. The reason for this is not clear. Age, degree of mental retardation, patients' peculiar habits, and other factors may affect the incidence (3,4).
The relationship of the outbreaks in the two institutions remains obscure, but they could be related since four of the residents in institution A had once been residents of institution B and since one short-stay individual in institution B acquired the parasite.

REFERENCES

  1. Ritchie, L.S. (1948): An ether sedimentation technique for routine stool examination. Bull. U.S. Army Med. Dept., 8, 326.
  2. Sanuki, J., Asai, T., Okuzawa, E., Kobayashi, S. and Takeuchi, T. (1977): Identification of Entamoeba histolytica and E. dispar cysts in stool by polymerase chain reaction. Parasitol. Res., 83, 96-98.
  3. Sargeaunt, P.G. and Williams, J.E. (1982): A study of intestinal protozoa including non-pathogenic Entamoeba histolytica from patients in a group of mental hospitals. Am. J. Pub. Health., 72, 178-179.
  4. Nagakura, K., Tachibana, H., Tanaka, T., Kaneda, Y., Tokunaga, M., Sasao, M. and Takeuchi, T. (1989): An outbreak of amebiasis in an institution for the mentally retarded in Japan. Jpn. J. Med. Sci. Biol., 42, 63-76.

*Corresponding author: Fax:+81-6-6772-0676, E-mail: HZH02210@niftyserve.or.jp

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