when did until 13 months ago patient 86206 last receive a microbiology test?
select microbiologyevents.charttime from microbiologyevents where microbiologyevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 86206 ) and datetime(microbiologyevents.charttime) <= datetime(current_time,'-13 month') order by microbiologyevents.charttime desc limit 1