A 12-Year-Old Girl Is Brought to the Office for Evaluation

A 12-year-old girl is brought to the office for evaluation of diarrhea that has been persistent over the past month.  The patient has had 2 or 3 loose, greasy, foul-smelling stools a day and describes feeling "bloated and gassy."  Her appetite is significantly decreased, and she has lost approximately 0.91 kg (2 lb) .  She has had no emesis or fever.  Her parents and 16-year-old sister do not have diarrhea, and the family is not sure if the patient had any sick contacts with similar symptoms.  Medical history is unremarkable and she takes no medications.  She and her classmates went on a wilderness hiking trip 6 weeks ago, but there has been no other recent travel.  Physical examination reveals hyperactive bowel sounds in all 4 quadrants but is otherwise unremarkable.  Stool microscopy is positive for multiple cysts and several flagellated trophozoites with 2 nuclei, and the patient is started on antimicrobial therapy.  In light of these results, classmates at her school undergo screening at the community health center, and stool samples from 4 of 26 students are positive for the same cysts.  Which of the following is the best strategy to eliminate further spread of this infection?

A) All classmates should receive antimicrobial therapy, regardless of symptoms or stool results
B) All classmates with positive stool samples should receive antimicrobial therapy, regardless of symptoms
C) Consistent alcohol-based hand sanitization should be encouraged to prevent further spread of the infection
D) Symptomatic students with positive stool samples should refrain from attending school
E) Symptomatic students with positive stool samples should refrain from using recreational water venues