calculate the number of patients that had a peritoneal fluid microbiology test since 5 years ago.
select count( distinct admissions.subject_id ) from admissions where admissions.hadm_id in ( select microbiologyevents.hadm_id from microbiologyevents where microbiologyevents.spec_type_desc = 'peritoneal fluid' and datetime(microbiologyevents.charttime) >= datetime(current_time,'-5 year') )