instruction: what was the last time patient 3911 got the rapid respiratory viral antigen test microbiology test on the first hospital visit?
response: SELECT microbiologyevents.charttime FROM microbiologyevents WHERE microbiologyevents.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 3911 AND NOT admissions.dischtime IS NULL ORDER BY admissions.admittime LIMIT 1) AND microbiologyevents.spec_type_desc = 'rapid respiratory viral antigen test' ORDER BY microbiologyevents.charttime DESC LIMIT 1