how many patients have had a blood (ebv) microbiology test performed since 2100?
select count( distinct admissions.subject_id ) from admissions where admissions.hadm_id in ( select microbiologyevents.hadm_id from microbiologyevents where microbiologyevents.spec_type_desc = 'blood (ebv)' and strftime('%y',microbiologyevents.charttime) >= '2100' )