what was the last time patient 3911 got the rapid respiratory viral antigen test microbiology test on the first hospital visit?
select microbiologyevents.charttime from microbiologyevents where microbiologyevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 3911 and admissions.dischtime is not null order by admissions.admittime asc limit 1 ) and microbiologyevents.spec_type_desc = 'rapid respiratory viral antigen test' order by microbiologyevents.charttime desc limit 1