when did patient 3369 first get pleural fluid's microbiology test during their last hospital visit?
select microbiologyevents.charttime from microbiologyevents where microbiologyevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 3369 and admissions.dischtime is not null order by admissions.admittime desc limit 1 ) and microbiologyevents.spec_type_desc = 'pleural fluid' order by microbiologyevents.charttime asc limit 1