A 34-year-old man comes to the office to establish medical care. The patient recently emigrated from Eastern Asia. He has no chronic medical conditions but reports intermittent abdominal discomfort and episodic diarrhea over the past several months. He has also had occasional dry cough and throat irritation. Physical examination shows no abnormalities. Serologic testing for Strongyloides stercoralis IgG is positive. Detection of which of the following is most suggestive of active infection by the pathogen in this patient?

Question

A 34-year-old man comes to the office to establish medical care.  The patient recently emigrated from Eastern Asia.  He has no chronic medical conditions but reports intermittent abdominal discomfort and episodic diarrhea over the past several months.  He has also had occasional dry cough and throat irritation.  Physical examination shows no abnormalities.  Serologic testing for Strongyloides stercoralis IgG is positive.  Detection of which of the following is most suggestive of active infection by the pathogen in this patient?

Quizplus · Accepted Answer

11ec160b_3800_5543_9249_ef2149f88a95_MD0001_00 Strongyloides stercoralis is a roundworm endemic to tropical and subtropical areas of Southeast Asia, Africa, and Western Pacific nations. It is transmitted when filariform larvae (infective) in soil contaminated with human feces come into direct contact with skin (eg, walking barefoot on the beach). The larvae penetrate the site of contact, migrate through the bloodstream/lymphatics to the lungs, and enter the alveoli. They then ascend the tracheobronchial tree and are swallowed. In the duodenum and jejunum, the larvae mature into adult worms, enter the intestinal mucosa, and secrete rhabditiform larvae (noninfective) that are excreted in stool. A minority of rhabditiform larvae mature to filariform larvae and reinfect the host through the intestinal mucosa or perianal skin (autoinoculation). Most patients are asymptomatic, but pulmonary (eg, dyspnea, wheezing, dry cough) or gastrointestinal symptoms (eg, constipation, diarrhea, abdominal pain) can occur. Patients may also develop linear, pruritic, erythematous streaks (larva currens) on the thighs and buttocks due to subcutaneous migration of filariform larvae after autoinoculation of the perianal skin. Although serology can aid in the diagnosis, positive S stercoralis IgG can indicate current or resolved infection (IgG often persists following eradication); active infection is diagnosed when rhabditiform larvae are identified in stool. Eggs and adult parasites are usually seen only in intestinal biopsies. (Choice A) Echinococcus is an animal tapeworm (eg, dogs, sheep) that can cause large liver cysts and pulmonary symptoms in humans. It is usually diagnosed with a combination of imaging (eg, hydatid cysts are visualized on liver ultrasound) and serologic tests. (Choice B) Enterobius vermicularis (pinworms) migrate out of the anus at night to deposit eggs on the surrounding perianal folds. Eggs can be detected by examining a piece of adhesive tape briefly applied to the perianal region shortly after the patient awakens. Perianal itching usually occurs. (Choice C) Intestinal tapeworms (eg, Taenia solium, Taenia saginata, Diphyllobothrium latum) are flatworms made up of multiple segments (proglottids). These are shed from the distal end of the worm and can be detected in the stool of infected individuals. Most cases are asymptomatic. (Choice E) Trophozoites and cysts are seen in the stool of patients with intestinal protozoal infections caused by Giardia intestinalis and Entamoeba histolytica. Patients typically have diarrhea but no pulmonary symptoms. Educational objective: Strongyloides stercoralis infection occurs when filariform (infective) larvae in contaminated soil penetrate human skin, travel to the lungs through the bloodstream/lymphatics, and ascend the tracheobronchial tree to be swallowed. They then enter the small intestine, mature, and reside in the mucosa. Rhabditiform (noninfective) larvae are excreted into the stool and can be detected on stool microscopy, which is diagnostic. __________ References: Strongyloides stercoralis in the immunocompromised population. (http://www.ncbi.nlm.nih.gov/pubmed/14726461)

A 34-Year-Old Man Comes to the Office to Establish Medical