1423Clinical Utility Of Incubating Anaerobic cultures 2 vs 5 Days

Abstract

Background. Clinical microbiology references suggest that cultures for anaerobic bacteria should be incubated for 5 days (d); however, little data exist to support this recommendation. A Quality Assurance (QA) study performed in our laboratory in 1992 revealed that most anaerobes were detected within 2 d and that the incremental yield of 5 d of incubation was negligible. We have repeated this analysis using contemporary reagents and methods to reevaluate the relative yield of anaerobes after 2 d vs 5 d of incubation. In addition, we assessed the clinical utility of the identification of isolates grown after 2 d of incubation.Methods. We performed an 8 month prospective QA study between August 1, 2013, and March 31, 2014. Specimens from sterile body fluids; wounds, tissues, abscesses, aspirates and operative specimens were inoculated to appropriate media, and placed into chambers with anaerobic atmosphere generated by the Anoxamat system. Cultures were incubated for 2 d before being examined.Cultures that showed no growth after 2 d were re-incubated for an additional 3 d and then re-examined at 5 d. Chart review was performed on anaerobic cultures that were positive only after 5 d.Results. A total of 2107 anaerobic cultures were processed during the study period, of which 177 specimens (8.3%) grew anaerobes. Only 2 (1.2%) were positive at 5 d and not at 2 d; 175/177 (99.4%) anaerobes were detected after 2 d of incubation. Propionibacterium acnes was isolated from the 2 positive specimens that grew only after 5 d of incubation. One of the 2 P. acnesisolates, which was from brain tissue, was judged to be clinically important. Thus, 1 of 177 clinically important anaerobic cultures (0.6%) would have been missed with a 2 d incubation protocol.Conclusion. Our results generally confirm observations from two decades ago. We conclude that the great majority of anaerobic cultures will show growth within 2 d of incubation. Rarely, particularly for P. acnes,longer incubation (e.g., 5 d) is needed. Infectious Diseases physicians should be aware of incubation protocols in their Microbiology labs and may wish to request extended incubation when clinically indicated. In an era of cost containment, in-house QA studies can enhance cost effective microbiology.Disclosures. All authors: No reported disclosures.Poster Abstracts • OFID 2014:1 (Suppl 1) • S369 Downloaded from https://academic.oup.