what was the name of the organism found at the last pleural fluid test of patient 23070 since 20 months ago?
select microbiologyevents.org_name from microbiologyevents where microbiologyevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 23070 ) and microbiologyevents.spec_type_desc = 'pleural fluid' and microbiologyevents.org_name is not null and datetime(microbiologyevents.charttime) >= datetime(current_time,'-20 month') order by microbiologyevents.charttime desc limit 1