阿米巴社區聚集事件之處置

中華 民國防疫學會

王任賢 理事長

Amebiasis基礎篇

The parasite exists in two forms, a cyst stagewhich is the infective form, and a trophozoite stage which is the form that causes invasive disease.

Infection occurs following ingestion of amebic cysts; this is usually via contaminated food or water but can be associated with venereal transmission through fecal-oral contact, particularly in sexually active homosexuals.

Cysts can remain viable in the environment for weeks to months, and ingestion of a single cyst is sufficient to cause disease.

The cysts pass through the stomach to the small intestine where they excyst to form trophozoites. The trophozoites can invade and penetrate the mucous barrier of the colon causing tissue destruction and increased intestinal secretion, and can thereby ultimately lead to bloody diarrhea.

It has become progressively apparent over the last 15 to 20 years that intestinal amebae with identical morphologic appearances can in fact be one of three species, E. histolytica or E. dispar or E. moshkovskii.

The clinical importance is that E. dispar and E. moshkovskii are non-pathogenic and do not cause clinical disease; thus all symptomatic disease is caused by E. histolytica.

Recommendations for diagnosis

Antigen detection assays are the best current means for diagnosing intestinal amebiasis since they are sensitive, specific, rapid, easy to perform and distinguish E. histolytica from E. dispar infections.

Antibody measurements are also available but remain positive for years. Stool specimens for microscopy are far less sensitive than antigen detection and cannot differentiate between the species.

TREATMENT E. dispar and E. moshkovskii infections does

not require treatment, whereas even asymptomatic E. histolytica infection should be treated because of the potential risk of developing invasive disease and the risk of spread to family members.

In countries where amebic infections are endemic, asymptomatic patients incidentally found to have stools positive for amebae are often presumed to have infection with E. dispar/E. moshkovskii and are not further evaluated or treated.

When antigen tests that can differentiate between E. dispar/E. moshkovskii and E. histolytica are more widely available in these countries, this practice may change.

Metronidazole The goals of antibiotic therapy of intestinal

amebiasis are both to eliminate the invading trophozoites and to eradicate intestinal carriage of the organism.

Metronidazole (500 to 750 mg PO three times daily for 7 to 10 days in adults and 35 to 50 mg/kg per day in three divided doses for 7 to 10 days in children) is the usual treatment for invasive colitis. The cure rate is approximately 90 percent.

Metronidazole is so well absorbed from the gastrointestinal tract that intravenous therapy offers no significant advantage as long as the patient can take oral medications and has no major defect in small bowel absorption.

A small number of patients have been treated with 2 g/day for three days, but cure rates were only 55 to 59 percent. Metronidazole resistance in E. histolytica trophozoites has not been reported.

Alternative drugs In countries where they are available,

tinidazole and ornidazole are alternative therapies. Tinidazole (2 g PO daily for three days) has a cure rate of 90 to 93 percent. It has been approved for the treatment of amebiasis by the United States Food and Drug Administration (FDA).

Agents for eliminating luminal cysts Following therapy for invasive amebiasis

with a nitroimidazole, treatment with a luminal agent may be required to eliminate intraluminal encysted organisms.

A ten day course of metronidazole will eliminate intraluminal infection in many cases, but a second agent is still recommended.

Intraluminal infection can be treated with one of the following regimens:

Paromomycin — 25-30 mg/kg per day orally in three divided doses for 7 days

Diiodohydroxyquin (iodoquinol) — 650 mg orally three times daily for 20 days for adults and 30-40 mg/kg per day in 3 divided doses for 20 days for children

Diloxanide furoate — 500 mg orally three times daily for 10 days for adults and 20 mg/kg per day in 3 divided doses for 10 days for children; this drug is not currently available in the United States.

Parasitologic cure rates are approximately 86 to 90 percent. Follow-up stool examinations are required after completion of the therapysince no regimen is completely effective.

Recommendations for Tx Metronidazole (500 to 750 mg PO three times

daily for 7 to 10 days in adults and 35 to 50 mg/kg per day in three divided doses for 7 to 10 days in children) is the usual treatment for invasive colitis.

Patients with invasive colitis should generally be treated with a luminal agent following a nitroimidazole. Paromomycin and diiodohydroxyquin (iodoquinol) are available in the United States.

Asymptomatic patients with E. histolytica (and not E. dispar/E. moshkovskii) should be treated with an intraluminal agent alone.

An outbreak of Amebiasis spread by colonic irrigation

at a chiropractic clinic

Gregory R. Istre et alNEJM 1982 Aug 5;307(6):339-42

緣起

1981年1月有醫師向科羅拉多州衛生局通報二名因灌腸引起的阿米巴痢疾

衛生局介入調查發現自1978年6月至1980年12月已經有至少36例阿米巴病例

歸納風險因子，這些病例均有在美國科羅拉多州西部之某診所接受過洗腸(colonic irrigation therapy)

其中10人後來切除大腸，6人死亡

回溯調查

這四年間此診所共看過176位病患，其中80人接受過colonic irrigation，96人接受其他治療

Bloody diarrhea Colonic irrigation group: 32% Non irrigation group:1%

Diagnosed as amebic infection (serology or pathology) Colonic irrigation group: 37% Non irrigation group:2.4%

探討

動物實驗中，直接將阿米巴種入大腸是會造成感染的。

本案是因為共用irrigation machine而感染，加上沒有例行的清理機器，病人通常要每日irrigation，共治療二週，因此機器會重覆感染。

Mass infection with Entamoeba histolytica in a Japanese institution

for individuals with mental retardation: epidemiology and control measures

S. Nishise et alAnn Trop Med Parasito 2010

Jul;104(5):383-90

緣起

日本山形縣某智能不足收容單位1996年通報一例阿米巴痢疾，2002年再度通報一例。

第二例的出現讓日本衛生單位開始介入調查

山形縣智能不足病患收容所

共收容76名成人智能不足病患，年齡在23-63歲中間

其共有四個收容病房，分別為輕到中度智能不足的男性病房及女性病房、及重度智能不足的男性病房及女性病房

每個病房均有獨立的公共廁所及浴室，病房的病患平時並不互相交流，只有吃飯在共同的餐廳用餐

討論: I 智能不足收容所爆發阿米巴聚集事件，在世界各國均有報告，單位內盛行率約為2-40% ，此次山形縣之盛行率為53% ，非常高

此次的事件是由於一位由神奈川縣(400公里外)移入的智能不足病患所引起。此病患1995年移入，移入前曾接受過metronidazole治療，但未追蹤是否治癒。在其移入一年後，首例病例出現。事件是經由菌株基因分析，發現山形現的聚集事件竟然與神奈川縣的雷同，才偵測出此移入病患。

討論：II 阿米巴為糞口傳染，可經由食入成熟的阿米巴

cyst而感染。智能不足者常會有吃大便或玩大便的怪異行為，所以阿米巴在智能越不足的人盛行率越高，可見一斑。

但男多於女比較難解釋，可能是由於最初的帶原者是男性的關係。

討論：III 雖然大部分的感染病例可由治療或是再治療而得到控制，但提升個人與環境衛生仍然很重要。

這可由病例並不局限於病人，治療後的再發病例也不局限於高度智障者，可見衛生習慣也扮演重要的傳播角色。

阿米巴的cyst在環境中可存活數周，所以洗手很重要。

討論：IV 一陣時間的定期篩檢對智能不足收容中心是很重要的，即使案例已經到零了，因為常會再發

新入住之住民一定要仔細查一下是否有阿米巴感染，就像本案僅一例入住病人就產生這麼多問題

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