instruction: how many patients have undergone a stool (received in transport system) test in 2105?
response: SELECT COUNT(DISTINCT admissions.subject_id) FROM admissions WHERE admissions.hadm_id IN (SELECT microbiologyevents.hadm_id FROM microbiologyevents WHERE microbiologyevents.spec_type_desc = 'stool (received in transport system)' AND STRFTIME('%y', microbiologyevents.charttime) = '2105')