Usefulness of routine pairing of anaerobic with aerobic blood culture bottles and decision making on antimicrobial therapy

ObjectivesTo evaluate the growth concordance in paired aerobic/anaerobic sets, and the impact of the anaerobic growth on patients' antimicrobial management.MethodThis is a prospective multicenter study which was conducted in three hospitals, with total beds of 750 beds and 52 ICU beds. Prospectively, laboratory blood cultures logbooks were daily reviewed and patients from whom blood cultures were ordered were followed, their chart were reviewed. Entries on antimicrobial therapeutic changes were noted for all paired sets. Clinicians were blinded to the study, though they were informed about culture results via the usual work protocol in each hospital.ResultsCollected Blood culture sets totaled 2492; 172 single sets were excluded, and 1160 paired sets were analyzed. 1046 were concordant; 79 sets had bacterial growth and 967 sets had no bacterial growth. 114 sets were discordant; 97 in aerobic bottles, 13 in anaerobic, and 4 in both.The proportion of agreement for the concordant paired growth sets was 90.2%.  The composite proportion of agreement for sets with any growth (N = 193, composite proportion of agreement = 56%, 95% C.I., 34% - 48%). Cohen kappa composite agreement, measured for the total analyzed paired-sets (N = 1160, K = .52, SE = .038. 95% C.I., .447 - .595). The odds of modifying antimicrobial regimen were for total and subgroups intent to treat odds, based on paired sets showed that one modification took place in one anaerobic growth set (N = 1160, Odds = 0.0008), the odds for all sets with any growth (N = 193, odds = .005), and based on any anaerobic sets (79 concordant, 13 anaerobic, and 4 discordant) with bacterial growth (N = 96: odds = 0.010).ConclusionThe study demonstrates that the proportion of agreement among paired sets were high, and needless to include anaerobic sets in routine blood culture collection. Also the decision-making of anti-infective treatment on patients based on anaerobic blood culture growth was not evident.