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Emergency And Acute Medicine - Giardiasis
Basics Description
Giardiasis is a noninvasive diarrheal illness caused by a protozoan parasite and is found worldwide. Prevalence ranges from 2–15% in developed countries and 20–40% in developing nations. It accounts for approximately 5% of travelers’ diarrhea and is the most common intestinal parasitic infection in the United States. Incidence peaks in early summer through fall, with highest rates in children aged 1–9 years and adults aged 30–39 years. Transmission occurs via the fecal–oral route. Humans are the primary reservoir, but domestic and wild mammals and contaminated surface water also serve as reservoirs. Populations at increased risk include travelers to endemic or wilderness areas, children in day care centers and their contacts, institutionalized individuals, and those engaging in anal sexual practices.
Etiology
Giardia lamblia is a flagellated protozoan, also known as Giardia intestinalis or Giardia duodenalis. After ingestion, organisms attach to intestinal villi and disrupt brush-border enzymes, leading to impaired digestion of lactose and other carbohydrates. No toxin is produced.
Diagnosis Signs And Symptoms
Symptoms typically begin 1–2 weeks after exposure. Infection is often asymptomatic. Symptomatic disease usually presents with acute-onset diarrhea that is foul-smelling, nonbloody, and frequently associated with steatorrhea. Illness is usually self-limited within 2–4 weeks but may be more severe in immunocompromised patients or those with underlying bowel disease. Common associated symptoms include flatulence, bloating, abdominal cramping, nausea, vomiting, malaise, anorexia, and weight loss. Fever is uncommon.
Thirty to fifty percent of patients develop chronic infection lasting longer than four weeks, characterized by fat malabsorption, secondary lactase deficiency, and macrocytic anemia due to folate deficiency. Pediatric patients may develop severe dehydration in acute disease and failure to thrive, growth retardation, or cognitive impairment in chronic infection. Physical examination is often benign. Extraintestinal manifestations include polyarthritis, urticaria, aphthous ulcers, maculopapular rash, and biliary tract disease.
Essential Workup
Evaluation should focus on exposure history, travel, high-risk group membership, and hydration status. The presence of gross or occult blood on rectal examination makes giardiasis unlikely.
Diagnosis Tests And Interpretation
Stool microscopy for ova and parasites has a sensitivity of 50–70% with one sample and up to 85–90% with three samples collected over several days. Specificity approaches 100%. Stool antigen detection by ELISA or immunofluorescent assay is highly sensitive and specific but does not detect other parasites. Stool PCR offers near-perfect sensitivity and specificity. Fecal leukocytes and stool cultures are unnecessary unless invasive bacterial infection is suspected. CBC may show macrocytic anemia in chronic disease. Electrolytes and renal function should be assessed if dehydration is present. Imaging studies are nonspecific and rarely required.
Differential Diagnosis
Viral gastroenteritis, bacterial enteritis, other protozoal infections, inflammatory bowel disease, irritable bowel syndrome, lactase deficiency, tropical sprue, medication or toxin-induced diarrhea, endocrine disorders, and gastrointestinal malignancy.
Treatment Initial Stabilization Therapy
Assess airway, breathing, and circulation. Administer intravenous isotonic fluids for significant dehydration. Children with severe dehydration require rapid fluid boluses and glucose monitoring.
Ed Treatment Procedures
Oral rehydration is sufficient for mild dehydration. Correct electrolyte abnormalities. Obtain stool studies when possible. If stool testing is negative but suspicion remains high, empiric treatment with metronidazole may be considered, and gastroenterology referral arranged for persistent symptoms.
Medication
First-line therapy includes metronidazole or tinidazole, each achieving cure rates near 90%. Metronidazole is given for 5–10 days, while tinidazole is administered as a single dose. Second-line agents include albendazole, nitazoxanide, quinacrine, paromomycin, or furazolidone when first-line therapy fails. Treatment choice should consider age, pregnancy status, renal function, and G6PD deficiency. Immunocompromised patients may require combination or prolonged therapy.
Follow-Up Disposition
Admission is indicated for patients with hemodynamic instability, severe electrolyte imbalance, inability to tolerate oral intake, or significant comorbid illness. Most patients can be discharged once hydration is adequate and symptoms are controlled.
Follow-Up Recommendations
Gastroenterology referral is recommended for persistent symptoms beyond four weeks despite therapy. Patients should be counseled regarding possible prolonged lactose intolerance and postinfectious fatigue.
Clinical Insights And Common Errors
Diagnosis is the primary challenge. Giardiasis should be considered in all patients with diarrhea, even without classic risk factors. A single stool specimen is often insufficient to exclude infection. Failure to recognize chronic disease and malabsorption can delay appropriate treatment.
Basics Description
Giardiasis is a noninvasive diarrheal illness caused by a protozoan parasite and is found worldwide. Prevalence ranges from 2–15% in developed countries and 20–40% in developing nations. It accounts for approximately 5% of travelers’ diarrhea and is the most common intestinal parasitic infection in the United States. Incidence peaks in early summer through fall, with highest rates in children aged 1–9 years and adults aged 30–39 years. Transmission occurs via the fecal–oral route. Humans are the primary reservoir, but domestic and wild mammals and contaminated surface water also serve as reservoirs. Populations at increased risk include travelers to endemic or wilderness areas, children in day care centers and their contacts, institutionalized individuals, and those engaging in anal sexual practices.
Etiology
Giardia lamblia is a flagellated protozoan, also known as Giardia intestinalis or Giardia duodenalis. After ingestion, organisms attach to intestinal villi and disrupt brush-border enzymes, leading to impaired digestion of lactose and other carbohydrates. No toxin is produced.
Diagnosis Signs And Symptoms
Symptoms typically begin 1–2 weeks after exposure. Infection is often asymptomatic. Symptomatic disease usually presents with acute-onset diarrhea that is foul-smelling, nonbloody, and frequently associated with steatorrhea. Illness is usually self-limited within 2–4 weeks but may be more severe in immunocompromised patients or those with underlying bowel disease. Common associated symptoms include flatulence, bloating, abdominal cramping, nausea, vomiting, malaise, anorexia, and weight loss. Fever is uncommon.
Thirty to fifty percent of patients develop chronic infection lasting longer than four weeks, characterized by fat malabsorption, secondary lactase deficiency, and macrocytic anemia due to folate deficiency. Pediatric patients may develop severe dehydration in acute disease and failure to thrive, growth retardation, or cognitive impairment in chronic infection. Physical examination is often benign. Extraintestinal manifestations include polyarthritis, urticaria, aphthous ulcers, maculopapular rash, and biliary tract disease.
Essential Workup
Evaluation should focus on exposure history, travel, high-risk group membership, and hydration status. The presence of gross or occult blood on rectal examination makes giardiasis unlikely.
Diagnosis Tests And Interpretation
Stool microscopy for ova and parasites has a sensitivity of 50–70% with one sample and up to 85–90% with three samples collected over several days. Specificity approaches 100%. Stool antigen detection by ELISA or immunofluorescent assay is highly sensitive and specific but does not detect other parasites. Stool PCR offers near-perfect sensitivity and specificity. Fecal leukocytes and stool cultures are unnecessary unless invasive bacterial infection is suspected. CBC may show macrocytic anemia in chronic disease. Electrolytes and renal function should be assessed if dehydration is present. Imaging studies are nonspecific and rarely required.
Differential Diagnosis
Viral gastroenteritis, bacterial enteritis, other protozoal infections, inflammatory bowel disease, irritable bowel syndrome, lactase deficiency, tropical sprue, medication or toxin-induced diarrhea, endocrine disorders, and gastrointestinal malignancy.
Treatment Initial Stabilization Therapy
Assess airway, breathing, and circulation. Administer intravenous isotonic fluids for significant dehydration. Children with severe dehydration require rapid fluid boluses and glucose monitoring.
Ed Treatment Procedures
Oral rehydration is sufficient for mild dehydration. Correct electrolyte abnormalities. Obtain stool studies when possible. If stool testing is negative but suspicion remains high, empiric treatment with metronidazole may be considered, and gastroenterology referral arranged for persistent symptoms.
Medication
First-line therapy includes metronidazole or tinidazole, each achieving cure rates near 90%. Metronidazole is given for 5–10 days, while tinidazole is administered as a single dose. Second-line agents include albendazole, nitazoxanide, quinacrine, paromomycin, or furazolidone when first-line therapy fails. Treatment choice should consider age, pregnancy status, renal function, and G6PD deficiency. Immunocompromised patients may require combination or prolonged therapy.
Follow-Up Disposition
Admission is indicated for patients with hemodynamic instability, severe electrolyte imbalance, inability to tolerate oral intake, or significant comorbid illness. Most patients can be discharged once hydration is adequate and symptoms are controlled.
Follow-Up Recommendations
Gastroenterology referral is recommended for persistent symptoms beyond four weeks despite therapy. Patients should be counseled regarding possible prolonged lactose intolerance and postinfectious fatigue.
Clinical Insights And Common Errors
Diagnosis is the primary challenge. Giardiasis should be considered in all patients with diarrhea, even without classic risk factors. A single stool specimen is often insufficient to exclude infection. Failure to recognize chronic disease and malabsorption can delay appropriate treatment.
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