Is treatment required for Blastocystis hominis infection in the absence of diarrhea?

Treatment of Blastocystis hominis in the Absence of Diarrhea

Treatment is not recommended for Blastocystis hominis infection in the absence of diarrhea or other persistent gastrointestinal symptoms.

Understanding Blastocystis hominis

• Blastocystis hominis is a unicellular organism commonly found in the intestinal tract of humans and animals 1
• The pathogenicity of Blastocystis hominis remains controversial, and in the absence of other pathogens, it may only be clinically relevant if symptoms persist 2
• Blastocystis can exist in several morphological forms including vacuolar, granular, ameboid, cyst, avacuolar, and multivacuolar forms 1

When to Consider Treatment

• Therapy should be limited to patients with persistent symptoms after a complete workup for alternative etiologies 3
• Treatment is indicated when:
  • Persistent diarrhea is present 3
  • Abdominal pain, nausea-vomiting, or flatulence persists for more than 2 weeks 3
  • No other pathogen is identified as the cause of symptoms 2
  • The organism is present in large numbers (five or more organisms per x400 field) 4

When NOT to Treat

• Asymptomatic carriers should not receive treatment 3
• Patients with incidental finding of Blastocystis without diarrhea or other GI symptoms do not require treatment 2
• In most people with acute watery diarrhea and without recent international travel, empiric antimicrobial therapy is not recommended regardless of the pathogen 2

Treatment Options When Indicated

• If treatment is warranted due to persistent symptoms, the following options may be considered:
  • Metronidazole is suggested as the drug of choice (30 mg/kg twice daily for 10 days in children; adult dosing varies) 3, 5
  • Trimethoprim-sulfamethoxazole has shown high efficacy (94.7% eradication in children, 93.3% in adults) 4
  • Saccharomyces boulardii (250 mg twice a day for 10 days) has shown comparable efficacy to metronidazole in symptomatic children 3

Diagnostic Considerations

• Infection is diagnosed by microscopic examination of stained smears or wet mounts of fecal material 1
• Most laboratories identify B. hominis by observing the vacuolar form, though other forms should also be sought for diagnosis 1
• Reporting semi-quantitative results (rare, few, many) may help determine clinical significance 2

Clinical Pitfalls to Avoid

• Treating asymptomatic carriers unnecessarily contributes to antimicrobial resistance without providing therapeutic benefit 6
• Misdiagnosing parasitic infections as bacterial infections can lead to inappropriate antibiotic use 7
• Failing to consider other causes of persistent diarrhea before attributing symptoms to Blastocystis 3
• Not completing the full course of antiparasitic treatment when treatment is indicated, which may lead to treatment failure 7

Follow-up

• If treatment is initiated for symptomatic infection, clinical response should be evaluated after completion of therapy 3
• Persistent symptoms despite appropriate treatment warrant further investigation for alternative diagnoses 3