Case Report: Lower Gastrointestinal Bleeding due to Entamoeba histolytica Detected Early by Multiplex PCR: Case Report and Review of the Laboratory Diagnosis of Amebiasis

Abstract.

We report a case of Entamoeba histolytica infection in a young man who presented with cerebral infarction and shortly after admission developed bloody diarrhea with fever. A rapid diagnosis of severe E. histolytica colitis was established through the use of a multiplex polymerase chain reaction enteropathogen stool panel. This result was unexpected in a patient native to the United States without known risk factors for amebiasis and negative stool microscopy examination for ova and parasites. Rapid diagnosis allowed prompt initiation of appropriate anti-amebic therapy and ultimately a good outcome in a condition that otherwise carries high morbidity and fatality.

CASE REPORT

A previously healthy 36-year-old man presented to the hospital with sudden-onset aphasia and right-sided hemiplegia secondary to a large ischemic left middle cerebral artery territory stroke with cortical swelling. His mental status declined following admission, along with development of new third cranial nerve palsy and uncal herniation with midline shift on repeat brain imaging, prompting emergent hemicraniectomy on hospital day 2. On hospital day 3, he had bright red blood per rectum evolving to bloody diarrhea and fever (39°C), with worsening leukocytosis (white blood cell count increased from 14.6 to 30.0 × 10⁹/L). Computed tomography (CT) of his abdomen revealed pancolitis with reactive mesenteric lymphadenopathy suggestive of infection (Figure 1). No abscess or fistula was seen. Clostridioides difficile was not detected in the stool by polymerase chain reaction (PCR), but a 22-target multiplex PCR panel detected Entamoeba histolytica (FilmArray GI panel; BioFire Diagnostics, Salt Lake City, UT), confirmed by repeat testing, while all other targets for bacterial, viral, and parasite pathogens were negative. Two stools submitted for ova and parasite examinations were both negative. Infectious workup was otherwise unremarkable, including chest radiograph and blood cultures.

Figure 1.

Computed tomography scan of the abdomen and pelvis with contrast showing diffuse wall thickening/submucosal edema involving the colon but most advanced in the cecum (arrow).

Additional history indicated no known gastrointestinal complaints before admission. He was a native of Virginia and had no significant travel history. Notable close contacts included several coworkers from Mexico at the restaurant where he had worked for over 10 years. In addition, his father was in the military, formerly stationed in Asia. He had no pets and no reported sexual contact with males. He drank bottled and municipal water but occasionally also drank water from a family well. He was not living with HIV and had no history of ever receiving corticosteroids or other immunosuppressant medications, including this hospitalization.

Microcytic anemia was detected on admission (hemoglobin 9.0 g/dL, mean corpuscular volume 81.8 fL) and iron deficiency was confirmed (serum iron 25 ug/dL, reference range 60–160 ug/dL; ferritin 4 ng/mL, reference range 20–275 ng/mL), for which he was treated. Evaluation for causes of cryptogenic stroke was unrevealing, including normal transthoracic echocardiogram with bubble study, vascular imaging, and no identified coagulopathy (including lack of antiphospholipid antibody, normal serum homocysteine level, and absent factor V Leiden mutation). He did have a history of smoking cigarettes, typically 0.5–1 pack per day for the past 11 years. Liver function tests were within normal range, and there was no evidence of extraintestinal amebiasis in the liver by abdominal imaging.

Our patient was treated for invasive amebiasis with metronidazole 500 mg three times daily for 10 days followed by the luminal agent paromomycin 1,000 mg three times daily (35 mg/kg/day) for an additional 7 days. His bloody diarrhea, fever, and leukocytosis improved with treatment. After 1 year of follow-up, he has been symptom free and without return of anemia (hemoglobin 17.1 g/dL with mean corpuscular volume 95 fL).

DISCUSSION

Our case describes a patient admitted for the management of cerebral infarction who developed bloody stools, fever, and leukocytosis secondary to severe amebic colitis. Amebiasis, caused by the protozoan parasite E. histolytica, is a leading cause of diarrhea globally, disproportionately affecting impoverished communities in developing countries. For example, in the large Global Enteric Multicenter Study, E. histolytica was one of the top 10 causes of moderate-to-severe diarrhea in children aged less than 5 years in two of their seven study sites across Asia and Africa.¹ In addition, E. histolytica diarrhea was associated with a relatively greater risk of death across all study sites and was the enteric pathogen with the highest hazard ratio for death in the second year of life.¹ In industrialized countries, most cases of amebiasis are imported, occurring primarily in either returning travelers or immigrants from endemic countries.² Travelers to South Asia, the Middle East, Africa, Mexico, Central, and South America appear to have the highest risk of acquiring amebiasis, particularly those engaging in missionary or other types of volunteering work.^2–5 Transmission is via fecal–oral ingestion of infective cysts, often through contaminated water and food, but sexual transmission among men who have sex with men has also emerged as an important risk factor for transmission, particularly in more developed countries.^2,6–11 Here in the United States, the prevalence of amebiasis is low, at about 4%,¹² but still represents one of the most common neglected tropical diseases affecting people living here.¹³ It is interesting that our case did not have any of the typical identifiable risk factors, as he was U.S.-born, had not traveled to an endemic area, and denied sexual activity with a partner with any of these risk factors. Transmission among household contacts has been described, so it is plausible that infection could have been related to close contact with coworkers, as the seroprevalence of E. histolytica is 8.4% in Mexico, reaching as high as 42% in some rural areas,^14,15 or perhaps from his father who had spent time in Asia. It is also not possible to time acquisition of his infection as invasive amebiasis can develop even 20 years or more after exposure.^16,17 Following ingestion, excysted trophozoites of E. histolytica remain in the colon, resulting in asymptomatic carriage; however, invasive disease occurs in 10–20% of those infected. The reasons for invasion are poorly understood.^18,19 About 1–2% of those infected will develop fulminant disease, which carries a high fatality, and more than 50% die with severe colitis if this develops.⁴ A significant risk factor for the development of severe and fulminant amebic disease is administration of corticosteroids.⁴ Associations with underlying immunocompromised status, pregnancy, age, diabetes, and alcoholism have also been reported.⁴ Other than being a critically ill adult male, it is not clear why our case developed such rapid and severe colitis; to our knowledge, he did not receive any corticosteroids or other immunosuppressive therapy during his admission. It is interesting to note that there is a well-described gender difference that occurs in amebiasis, with a higher occurrence of invasive disease in males.² More than 80% of amebic liver abscesses occur in adult men, for example.⁵ To our knowledge, neither intracranial infarction nor neurosurgery has been described as a risk factor for invasive amebic disease. A review of articles ever published was conducted on September 9, 2019, using the PubMed database with the following search terms: (“neurosurgical procedures”[MeSH Terms] OR (“neurosurgical”[All Fields] AND “procedures”[All Fields]) OR “neurosurgical procedures”[All Fields] OR “neurosurgery”[All Fields] OR “neurosurgery”[MeSH Terms]) AND (“entamoeba”[MeSH Terms] OR “entamoeba”[All Fields]). Nine publications were identified, the titles and abstracts were assessed, but no relevant case reports were found. A similar search was performed using the search terms intracerebral[All Fields] AND (“infarction”[MeSH Terms] OR “infarction”[All Fields]) AND (“entamoeba”[MeSH Terms] OR “entamoeba”[All Fields]), which yielded 0 publications, and (“stroke"[MeSH Terms] OR “stroke”[All Fields]) AND (“entamoeba”[MeSH Terms] OR “entamoeba”[All Fields]), which yielded three publications but no relevant reports.

When amebiasis is suspected, there are several methods available for diagnosis, and sometimes a combination of tests may be required (Table 1). The most widely used modality is stool microscopy.²⁰ Cysts and trophozoites can be visualized, sometimes with evidence of hemophagocytosis, by an experienced observer using wet mounts or stained preparations.²¹ Stool microscopy lacks sensitivity, as excretion is variable and trophozoites and cysts may be easily missed.²⁰ It should be noted that two separate stool samples were submitted from our case, both of which were negative in the face of active amebic colitis, reinforcing how poorly this test performs and the need to use superior tests if available. Stool microscopy also lacks specificity as E. histolytica is morphologically indistinguishable from the Entamoeba species of lesser or no pathogenic potential, namely, E. dispar, E. moshkovskii, and E. bangladeshi.^22–25 Stool antigen detection tests offer several advantages over stool microscopy including improved specificity, but performance may be variable depending on the clinical setting; for example, sensitivity may be reduced in low-endemic areas.^26,27 Stool antigen tests have the potential to serve as rapid tests in resource-limited endemic settings, as they are simple and easy to perform, but remain largely underused.²⁰ Molecular detection by PCR is the most sensitive way to detect amebiasis by stool or abscess fluid examination.²⁷ The turnaround time can be quite rapid when using an automated system. Multiplex gastrointestinal panels can detect multiple stool enteropathogens simultaneously.²⁷ We believe that the use of a multiplex gastrointestinal panel was beneficial in our case, given our low endemicity, with only ∼30 cases of amebiasis reported annually in the state of Virginia.²⁸ There were no other identifiable epidemiologic risk factors to suspect amebiasis in his case, so diagnosis may have been delayed otherwise. The rapid turnaround time allowed prompt initiation of appropriate therapy, ultimately contributing to a good treatment outcome of severe amebic colitis. Treatment of invasive amebic infection requires the use of an amebicidal tissue-active agent, such as metronidazole or tinidazole, followed by a luminal cysticidal agent, such as paromomycin, diloxanide, or iodoquinol.²⁰ Asymptomatic carriage can be treated with a luminal agent alone, to prevent the development of disease and transmission to others.²⁰ It is recommended that amebiasis be considered in patients with epidemiologic risk factors before starting on immunosuppressive therapy.⁴ It is particularly important to consider amebiasis in the differential diagnosis of those diagnosed with inflammatory bowel disease (IBD), as the clinical presentations may be indistinguishable.⁴ Severe or fulminant amebic colitis additionally requires fluid resuscitation and supportive care, and sometimes surgical intervention is necessitated.⁴ When a diagnosis of amebic colitis is made, abdominal imaging, such as ultrasonography, can be carried out to exclude the presence of amebic liver abscess, which may require drainage depending on the size and location. Liver abscess was not seen in our case by CT imaging of the abdomen. The differential diagnosis of colitis for our patient would include infectious bacterial and parasitic causes as well as IBD. The use of a multiplex PCR panel helped to exclude the possibility of 21 other enteropathogens, including bacterial causes of colitis, demonstrating the potential to serve as a powerful antimicrobial stewardship tool. The sensitivity and specificity of the commercial assay we used approaches 100% in the diagnosis of amebiasis, so we believe a false-positive test was unlikely.^29,30 In addition, the panel was repeated by our microbiology laboratory, given that this target was an unusual finding for our community and was still positive. Although metronidazole or other antibiotics may be considered as part of the treatment for infectious complications of IBD such as abscess formation or fistulous disease, metronidazole does not appear to be of benefit in the routine management of patients with acute, severe ulcerative colitis.³¹ The rapid response to metronidazole observed in our patient is much more suggestive of treatment of infection. In addition, our patient has not developed any clinical manifestations concerning for IBD after a year of follow-up. We believe that his iron-deficiency microcytic anemia was most likely caused by chronic microscopic gastrointestinal blood loss secondary to unrecognized amebic disease. He has not redeveloped anemia following appropriate treatment of this infection.

Table 1.

Summary of diagnostic methods available for the detection of amebiasis^{2,14,20,21,27}

Method	Sensitivity (%)	Specificity (%)	Attributes	Limitations	Notes
Stool microscopy	< 60	< 50	Widely available	Poor sensitivity	Fresh stools increase recovery
			Other stool parasites may be visualized at the same time	Does not differentiate from other Entamoeba species	Sensitivity improved with examination of multiple stools
			Minimal equipment and reagents required	Skilled observer required
Stool antigen detection	< 88	> 80	Simple, rapid, and easy to use	Sensitivity may be reduced in non-endemic settings	Requires fresh, not fixative preserved stool
			Some commercially available tests detect multiple enteroparasites
Stool PCR	> 92	> 89	Preferred test, very high sensitivity and specificity for the detection of enteric infection	More expensive, limiting availability in lower resource settings	Can also test abscess fluid by PCR
			Multiplex panels can detect multiple other viral, bacterial, and parasitic targets simultaneously	Requires specialized equipment, reagents, and skilled technicians
Serology	92	90	Useful adjunct to stool studies, particularly for amebic liver abscess and other forms of disseminated infection	Remains positive for years after resolution of infection, so of less utility in endemic settings	May need to repeat in 7–10 days if initially negative

PCR = polymerase chain reaction.

In summary, we report a good outcome in a patient with severe amebic colitis, affecting the entire large colon, who responded appropriately to medical therapy. Severe and fulminant forms of amebic colitis carry high rates of morbidity and fatality. The use of a multiplex gastrointestinal PCR panel contributed to rapid diagnosis and initiation of treatment in this patient, which we believe is a key contributor to his good outcome. This case also highlights the possibility of E. histolytica infection in patients in the United States without apparent epidemiologic risk factors for acquisition.