when did patient 96833 take the influenza a/b by dfa microbiology test for the first time during this month?
select microbiologyevents.charttime from microbiologyevents where microbiologyevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 96833 ) and microbiologyevents.spec_type_desc = 'influenza a/b by dfa' and datetime(microbiologyevents.charttime,'start of month') = datetime(current_time,'start of month','-0 month') order by microbiologyevents.charttime asc limit 1