count the number of patients who had received a microbiological test of the bronchoalveolar lavage 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 = 'bronchoalveolar lavage' and strftime('%y',microbiologyevents.charttime) >= '2100' )