instruction: when was the last sputum, expectorated microbiology test given to patient 031-15417 until 08/2104?
response: SELECT microlab.culturetakentime FROM microlab WHERE microlab.patientunitstayid IN (SELECT patient.patientunitstayid FROM patient WHERE patient.patienthealthsystemstayid IN (SELECT patient.patienthealthsystemstayid FROM patient WHERE patient.uniquepid = '031-15417')) AND microlab.culturesite = 'sputum, expectorated' AND STRFTIME('%y-%m', microlab.culturetakentime) <= '2104-08' ORDER BY microlab.culturetakentime DESC LIMIT 1