Investigation of Mycobacterium Pseudo-outbreak

BACKGROUND: A cluster of 8 Mycobacterium avium Complex (MAC) clinical acid-fast bacilli (AFB) cultures were identified in a 2-week period at an urban public university hospital system. A review of AFB cultures from the past year showed a surge of cases during the months of October to November from the typical 1-3 cases per month. METHODS: An internal evaluation demonstrated that the number of cultures growing MAC from 9/30/16-11/30/16 was considerably greater than it had been in preceding months. Chart review was performed to determine the clinical relevance of the MAC cultures. Of 8 initial patients identified 6 had no clinical syndrome consistent with MAC infection. In addition, there were no common collection locations to suggest contamination at collection. Microbiology laboratory practices were reviewed and AFB smear and culture preparation and genetic probe identification of AFB were observed. Reagents and stains were cultured and local laboratory and reagent manufacturers were contacted. RESULTS: MAC was identified in 22 cultures from October to December 2016. Culture sites included sputum (induced and bronchoalveolar lavage), tissue, body fluid and organ preservation fluid. Prior history of mycobacterial pulmonary disease was seen in 5 patients during this time. Providers did not start patients without a history of MAC on therapy. Species identification by rpoB gene sequencing was performed in 17 of 22 cultures. Nine (53%) isolates were M. chimaera followed by M. Avium with 5 (29%)isolates. One grew both M. Avium and Mycobacterium tuberculosis (MTB), while another isolate was identified as MTB. Review of laboratory practices, revealed opportunities for cross contamination when tasks were batched and alternated while awaiting incubation or amplification as all AFB processing took place under one hood. Culture of PANTA™ reagent grew M. chimera. CONCLUSION: Increased MAC cultures above baseline incidence identified a contamination of laboratory reagent causing a pseudo-outbreak of M. chimera. The pseudo-outbreak did not have clinical implication as patients lacked clinical signs and were not treated. Separation of amplification and culture preparation tasks both spatially and temporally are recommended to decrease cross contamination. DISCLOSURES: All authors: No reported disclosures.