1644. The Impact of Species Identification on the Diagnosis and Treatment of Rapidly Growing Mycobacteria
Session: Poster Abstract Session: Mycobacterial Infections
Saturday, October 5, 2013
Room: The Moscone Center: Poster Hall C
Background: There is limited literature addressing the clinical impact of speciation of rapidly growing mycobacteria (RGM) cultures.  Many clinical microbiology laboratories label them as nondescript RGM or under a broad complex such as “Mycobacterium chelonae-fortuitum complex” (MCFC) as is the case in our institution, unless species identification is requested.  We assessed the impact of reporting RGM as MCFC. 

Methods: Retrospective chart review of patients from January 2008 – April 2012 was conducted and data was collected and analyzed.  Selected isolates were submitted for molecular identification and susceptibility testing. 

Results:   Seventy-five patients had positive cultures for MCFC of which, 84% (63/75) were respiratory specimens.  Five percent (4/75) had ≥ 2 positive cultures for MCFC although 51% (32/63) had fewer than 3 sputum cultures performed.  Only 18% (3/17) had positive bronchoscopic cultures.  Respiratory specimens with MCFC grew another Mycobacterium species in 22% (14/63) of cases.  Underlying lung disease was found in 44% (28/63).  Ninety-five percent (53/56) did not fulfill the American Thoracic Society (ATS) criteria for nontuberculous mycobacteria (NTM) lung disease.  Fifteen percent (11/75) of patients were on antimycobacterial treatment for co-existent NTM or MCFC.  The most common therapy was a macrolide and/or a fluoroquinolone.  Previous macrolide resistant NTM occurred in 18% (2/11) of cases.  Speciation was performed in 35% (26/75) of cases, with 15 M. porcinum, 9 M. abscessus, 1 M. abscessus subsp. massiliense and 1 M. fortuitum identified.  Those with previous/co-existent NTM revealed 67% (4/6) of the isolates to be a different NTM species than previously identified.  Macrolide resistant isolates occurred in 75% (6/8) of those tested.  Sixty percent (6/10) of those being treated fulfilled the ATS criteria. 

Conclusion:   Most patients with positive cultures did not meet the ATS criteria for NTM lung disease.  The MCFC label was misleading because only one isolate was M. fortuitum and no M. chelonae was identified.  Clinicians did not consider other members of the RGM group (M. porcinum or M. abscessus) in regards to therapy.  This study supports the identification to species all RGM isolates in patients with history or suspicion of RGM disease.

Jeana L Benwill, MD1, A Scott Lea, MD1, Michael Loeffelholz, PhD2, Barbara A Brown-Elliott, MS3, Richard J Wallace, MD, FIDSA3 and Juan C Sarria1, (1)The University of Texas Medical Branch, Galveston, TX, (2)Pathology, The University of Texas Medical Branch, Galveston, TX, (3)The University of Texas Health Science Center, Tyler, TX


J. L. Benwill, None

A. S. Lea, None

M. Loeffelholz, None

B. A. Brown-Elliott, None

R. J. Wallace, None

J. C. Sarria, None

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