Laboratory diagnosis of parasites — MCQs

An 82-year-old woman presents with 2 months of foul-smelling, greasy diarrhea. She says that she also has felt very tired recently and has had some associated bloating and flatus. She denies any recent abdominal pain, nausea, melena, hematochezia, or vomiting. She also denies any history of recent travel and states that her home has city water. Which of the following tests would be most appropriate to initially work up the most likely diagnosis in this patient?

A 31-year-old male traveler in Thailand experiences fever, headache, and excessive sweating every 48 hours. Peripheral blood smear shows trophozoites and schizonts indicative of Plasmodia infection. The patient is given chloroquine and primaquine. Primaquine targets which of the following Plasmodia forms:

A 68-year-old man presents to his physician for symptoms of chronic weight loss, abdominal bloating, and loose stools. He notes that he has also been bothered by a chronic cough. The patient’s laboratory work-up includes a WBC differential, which is remarkable for an eosinophil count of 9%. Stool samples are obtained, with ova and parasite examination revealing roundworm larvae in the stool and no eggs. Which of the following parasitic worms is the cause of this patient’s condition?

A 27-year-old woman visits her family physician complaining of the recent onset of an unpleasant fish-like vaginal odor that has started to affect her sexual life. She was recently treated for traveler’s diarrhea after a trip to Thailand. External genitalia appear normal on pelvic examination, speculoscopy shows a gray, thin, homogenous, and malodorous vaginal discharge. Cervical mobilization is painless and no adnexal masses are identified. A sample of the vaginal discharge is taken for saline wet mount examination. Which of the following characteristics is most likely to be present in the microscopic evaluation of the sample?

A 45-year-old man visits the office with complaints of severe pain with urination for 5 days. In addition, he reports having burning discomfort and itchiness at the tip of his penis. He is also concerned regarding a yellow-colored urethral discharge that started a week ago. Before his symptoms began, he states that he had sexual intercourse with multiple partners at different parties organized by the hotel he was staying at. Physical examination shows edema and erythema concentrated around the urethral meatus accompanied by a mucopurulent discharge. Which of the following diagnostic tools will best aid in the identification of the causative agent for his symptoms?

The World Health Organization suggests the use of a new rapid diagnostic test for the diagnosis of malaria in resource-limited settings. The new test has a sensitivity of 70% and a specificity of 90% compared to the gold standard test (blood smear). The validity of the new test is evaluated at a satellite health center by testing 200 patients with a positive blood smear and 150 patients with a negative blood smear. How many of the tested individuals are expected to have a false negative result?

A 55-year-old man presents to the physician with complaints of 5 days of watery diarrhea, fever, and bloating. He has not noticed any blood in his stool. He states that his diet has not changed recently, and his family has been spared from diarrhea symptoms despite eating the same foods that he has been cooking at home. He has no history of recent travel outside the United States. His only medication is high-dose omeprazole, which he has been taking daily for the past few months to alleviate his gastroesophageal reflux disease (GERD). Which of the following is the most appropriate initial test to work up this patient’s symptoms?

A 62-year-old man is brought to the emergency department with fatigue, dry cough, and shortness of breath for 3 days. He reports a slight fever and has also had 3 episodes of watery diarrhea earlier that morning. Last week, he attended a business meeting at a hotel and notes some of his coworkers have also become sick. He has a history of hypertension and hyperlipidemia. He takes atorvastatin, hydrochlorothiazide, and lisinopril. He appears in mild distress. His temperature is 102.1°F (38.9°C), pulse is 56/min, respirations are 16/min, and blood pressure is 150/85 mm Hg. Diffuse crackles are heard in the thorax. Examination shows a soft and nontender abdomen. Laboratory studies show: Hemoglobin 13.5 g/dL Leukocyte count 15,000/mm3 Platelet count 130,000/mm3 Serum Na+ 129 mEq/L Cl- 100 mEq/L K+ 4.6 mEq/L HCO3- 22 mEq/L Urea nitrogen 14 mg/dL Creatinine 1.3 mg/dL An x-ray of the chest shows infiltrates in both lungs. Which of the following is the most appropriate next step in diagnosis?

A 22-year-old female presents to her physician for evaluation of a vaginal discharge, itching, and irritation. She recently started a new relationship with her boyfriend, who is her only sexual partner. He does not report any genitourinary symptoms. She takes oral contraceptives and does not use barrier contraception. The medical history is unremarkable. The vital signs are within normal limits. A gynecologic examination reveals a thin, yellow, frothy vaginal discharge with a musty, unpleasant odor and numerous punctate red maculae on the ectocervix. The remainder of the exam is normal. Which of the following organisms will most likely be revealed on wet mount microscopy?

A 54-year-old man comes to the physician because of diarrhea that has become progressively worse over the past 4 months. He currently has 4–6 episodes of foul-smelling stools per day. Over the past 3 months, he has had fatigue and a 5-kg (11-lb) weight loss. He returned from Bangladesh 6 months ago after a year-long business assignment. He has osteoarthritis and hypertension. Current medications include amlodipine and naproxen. He appears pale and malnourished. His temperature is 37.3°C (99.1°F), pulse is 76/min, and blood pressure is 140/86 mm Hg. Examination shows pale conjunctivae and dry mucous membranes. Angular stomatitis and glossitis are present. The abdomen is distended but soft and nontender. Rectal examination shows no abnormalities. Laboratory studies show: Hemoglobin 8.9 g/dL Leukocyte count 4100/mm3 Platelet count 160,000/mm3 Mean corpuscular volume 110 μm3 Serum Na+ 133 mEq/L Cl- 98 mEq/l K+ 3.3 mEq/L Creatinine 1.1 mg/dL IgA 250 mg/dL Anti-tissue transglutaminase, IgA negative Stool culture and studies for ova and parasites are negative. Test of the stool for occult blood is negative. Fecal fat content is 22 g/day (N < 7). Fecal lactoferrin is negative and elastase is within normal limits. Which of the following is the most appropriate next step in diagnosis?