during this hospital visit, when patient 42473 had the last csf;spinal fluid microbiology test?
select microbiologyevents.charttime from microbiologyevents where microbiologyevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 42473 and admissions.dischtime is null ) and microbiologyevents.spec_type_desc = 'csf;spinal fluid' order by microbiologyevents.charttime desc limit 1