Acute gastroenteritis due to Blastocystis hominis in an adolescent boy

Abstract

Acute gastroenteritis with persistent vomiting, high degree fever and blood streaking stools often suggests bacterial aetiology in children. Authors report a 13-year-old boy presenting with acute watery diarrhoea with persistent vomiting, fever of 103°F, abdominal cramps and blood streaking stools who failed to show any response to parenteral third-generation cephalosporin for 72 hours. The stool examination revealed numerous cystic and amoeboid forms of Blastocystis hominis. Metronidazole was started and the boy promptly responded within 24 hours. There was no recurrence of symptoms then onwards. The case highlights the crucial stool examination in case of acute diarrhoeal disease for rare aetiology.

Background

Blastocystis sp are the most common protozoa that infect the human gastrointestinal tract. The organism is generally seen in the colon and cecum of children. The usual mode of transmission is fecal–oral route. Its pathogenical role in humans has been confirmed by few studies.^1–3 The clinical manifestations include watery stool, nausea, decreased appetite, abdominal cramps, flatulence, urticarial rashes, increased secretion of saliva and itching at the anus. Fatigue and irritable bowel syndrome may also be present. Fever is uncommon. Stool examination confirms the diagnosis. Authors report an acute diarrhoea in a 13-year-old boy with fever, abdominal cramps and persistent vomiting causing diagnosis dilemma but the stool examination providing the crucial aetiology of Blastocystis hominis.

Case presentation

A previously healthy 13-year-old boy presented with 2-day history of fever, headache, persistent vomiting, pain abdomen and loose stools. The illness started with high-grade intermittent fever associated with chills and rigours followed by blood-streaked stools, which progressed to watery stools, non-foul smelling five to six times a day. He had severe abdominal cramps and multiple episodes of non-bilious, non-projectile, vomiting. There was no history of itching at anus, increased salivary secretion or skin rashes. Examination revealed fever of 103°F, tachycardia, normal blood pressure and dry tongue. Abdominal examination revealed generalised abdominal tenderness more pronounced in the left iliac fossa. Examination of other systems was normal.

Investigations

Complete blood count revealed total leucocyte count of 19.6×10⁹/L, neutrophils of 75%, Hb of 14.3 g%, platelet count of 249×10⁹/L, normal serum electrolytes, blood urea of 49 mg/dL, serum creatinine of 0.65 mg/dL and normal urine routine examination. C reactive protein (CRP) was 21 mg/L. Stool was sent for microscopy and culture.

Differential diagnosis

Acute gastroenteritis probably of bacterial aetiology would present with diarrhoea, vomiting and fever. The present case had these features; however, the stool examination and culture did not identify any bacteria. Another differential diagnosis is acute dysentery of bacterial or amoebic origin. The blood in stool, high fever, tenesmus and abdominal cramps are the likely features in bacterial dysentery. The stool examination and culture would help to identify Shigella sp. In amoebic dysentery, the stool examination would identify the organisms. In the present case, the stool examination and culture ruled out these possibilities.

Treatment

As he was unable to take any food orally, he was started on intravenous fluids and other symptomatic measures. Empirical intravenous ceftriaxone was started because of persistent fever spikes and blood-streaking stools. However, the child continued to have high fever spikes with intermittent colicky pain in abdomen causing lot of parental anxiety for next 48–72 hours. By then the stool microscopy reported numerous cystic and amoeboid forms of B. hominis. There were no other pathogens in the stool and the culture was sterile.

Outcome and follow-up

The treating team started intravenous metronidazole considering B. hominis as the pathogen. The clinical picture also favoured the diagnosis. Review of the history revealed consumption of food at a restaurant prior to the illness as a probable source of infection. He responded promptly within next 24 hours, the fever touched the baseline (figure 1), loose stools and pain in abdomen gradually decreased. There were no fever spikes further. He was discharged by next 3 days on oral metronidazole. He was asymptomatic after 2 weeks follow-up.

Figure 1.

The fever pattern before and after metronidazole initiation.

Discussion

B. hominis is an intestinal protozoon. The disease in humans has various manifestations. The pathogenical role of the organism especially with high parasite burden in humans has been reported mostly in adults.^{1 2} In the present case, the invasive nature of the organism and the crucial role of the stool microscopy in the diagnosis and appropriate management of gastroenteritis in a child have been reported.

The clinical manifestations of B. hominis include loose stools, nausea, decreased appetite, crampy abdominal pain, urticarial skin rashes, increased salivary secretion, severe itching in the anus and fatigue.^1–3 Fever is not commonly observed. Irritable bowel syndrome and diarrhoea lasting for many days are other manifestations. The average age of the patients being 46.3 years with a range between 13 and 85 years, blood in stools in 17 out of 80 patients, fever in two out of 80 patients, skin manifestations in 11.2% and elevated CRP levels have been reported by Bálint et al.² In the present case, there was high fever, blood in stool, severe abdominal pain and numerous cysts of parasite in the stool. The illness starting with blood-streaked stools, progressing to watery stools, rectal bleeding and biopsy-proven colonic ulceration in a 4-year-old child in Texas has been reported.³ The presence of five or more parasites in a microscopic field and the absence of other intestinal pathogens indicates the disease.

The diagnosis of B. hominis is established when characteristic forms of the parasites in faecal samples are detected. B. hominis has four distinct parasite forms—the cyst forms, the amoeboid forms, the granular forms and the vacuolar forms. Wet preparations of fresh stool are ideal to detect B. hominis. The stool concentration process does not help as the organism does not survive in such condition. Liquid stool specimens detect these pathogen more easily. If B. hominis is detected in the stool, an approximate quantification such as few, moderate or many would help the clinician to provide specific treatment. The cyst forms of the parasite resistant to chlorine treatment survive at high levels of the stomach acid. High parasite burden linked to pathogenicity, many cysts in stool needing treatment and metronidazole as the drug of choice have been reported by Coyle et al.¹ In the present case, numerous B. hominis cysts in the stool, absence of other pathogens and negative stool culture confirmed the diagnosis.

Treatment with specific drug is recommended for B. hominis. Metronidazole is considered a first-line treatment for Blastocystis infection.^{1 2 4} Resistance has been documented but quite rare. Other drugs recommended include paromomycin, ornidazole, albendazole, ivermectin, trimethoprim–sulfamethoxazole, furazolidone, nitazoxanide, secnidazole, fluconazole, nystatin and itraconazole. In conclusion, B. hominis should be considered as a causative agent of gastroenteritis in children with suggestive symptoms, especially when the parasite is present in large numbers in faecal specimens in the absence of other known pathogens.

Learning points.

• The acute gastroenteritis in children is caused by various microorganisms but the stool examination should not be forgotten.

• Blastocystis hominis should be considered as a causative agent of childhood diarrhoea especially when the parasite is present in large numbers in faecal samples in the absence of other known pathogens.

• Treatment of B. hominis gastroenteritis with metronidazole promptly relieves the symptoms and reduces the morbidity significantly.