471 - Utility of Anaerobic Blood Cultures in Neonatal Sepsis Evaluation

It is standard practice to send a single aerobic blood culture for neonatal sepsis evaluation. The benefit of sending a paired anaerobic blood culture remains unclear.

Objective: To determine if detection rate and time to positivity (TTP) of pathogen isolation in the anaerobic culture bottle differs from that of the paired aerobic blood culture bottle.

Design/Methods: Single center, retrospective cohort study of neonatal sepsis evaluations performed from 2015-2021. For sepsis evaluation, center practice was to inoculate 1 mL blood into BD BACTEC Peds Plus/F aerobic and 1 mL into BD BACTEC Plus anaerobic culture bottles. TTP was calculated from time of inoculation to time culture growth was first detected by the BD system. Common commensals were categorized as contaminants.  Coagulase negative staphylococci (CoNS) were considered pathogens when treated with an appropriate antibiotic for ≥5 days.

Results: During the study period, 4511 blood cultures were obtained from 3191 infants. Growth of an organism was noted in 259 cultures (6%) obtained from 125 infants (median gestational age 27 weeks (IQR 25.0 -34.3) and median birth weight 1013 grams (IQR 658, 245)). Of the 259 positive cultures, 180 were sent as aerobic-anaerobic pairs. After excluding contaminants (n=22), 158 aerobic-anaerobic culture pairs from 102 infants were analyzed. Pathogens were isolated from only 1 of 2 paired bottles in 65 episodes (41%); of these, pathogens were isolated from the anaerobic bottle alone in 31 (19%) episodes (Figure 1). Pathogens isolated solely in the anaerobic culture accounted for 18% of all Gram-negative and 14% of all non-CoNS Gram-positive bacteremia episodes (Table), and included one obligate anaerobe (Bacteroides fragilis) and 30 facultative anaerobes: 13 CoNS, 5 Staphylococcus aureus, 5 Escherichia coli, 2 Enterococcus faecalis, and 1 each of Enterobacter cloacae, Group B Streptococcus, Klebsiella pneumoniae, Morganella morgani, and Prevotella loescheii. When both bottles were positive (n=93, 59%), pathogens were isolated first in the anaerobic culture in 61 episodes (66%), with a difference in TTP ≥4 hours in 17 episodes (28%) (Figure 2).

Conclusion(s):

When sepsis evaluation included both aerobic and anaerobic cultures, pathogens were isolated from anaerobic cultures alone in 19% of cases. TTP was also shorter in 66% of cases. Our center experience suggests that the identification of neonatal bacteremia may be optimized with the use of both aerobic and anaerobic culture.