[1552] Identification of Fungi in Tissue: A Discrepancy between Histology/Cytology Versus Microbiology

Maksim Agaronov, Janice Tetreault, Luis Calderin, Jaber Aslanzadeh, Mary Fiel-Gan. Hartford Hospital, Hartford, CT

Background: Core biopsies and aspirates are procedures performed to help diagnose lung nodules and infiltrates. On occasion, a portion of this tissue is sent to microbiology, especially when infection is considered. The histologic assessment includes histochemical and immunohistochemical stains. The microbiology work-up includes direct smears with calcofluor-white (CW), tissue culture, and a 14-day fungal culture. Our goal was to find cases with tissue histology or cytology and corresponding microbial studies, then compare the turnaround time (TAT) and final diagnosis of the two methods of detection. The specificity and availability of the results may be extremely important especially with immunocompromised patients.
Design: We searched the Pathology Laboratory Information System from 1/2009 to 9/2012 for lung core and cytology biopsies with a positive diagnosis for fungi. Subsequently, we obtained corresponding smear, tissue, and fungal culture results from the Microbiology laboratory.
Results: A total of 22 histology/cytology cases were positive: 13 Aspergillus; 4 Rhizomucor; 1 Histoplasma; 2 Cryptococus; 1 Coccidioides; and 1 Blastomyces. Of the corresponding cases in microbiology, immediate direct smear with CW revealed 7 fungi: 4 septate hyphae, 2 aseptate hyphae, and 1 yeast. Subsequent fungal culture results were positive for 3 Aspergillus fumigatus (5-day) and 1 (diagnosed as Blastomyces on histology) for Cokeromyces recurvatus (7-day). The remaining 15 cases showed no growth. TAT was 2 days for histology, while direct smear and positive culture results were reported immediately.
Conclusions: Our study shows a marked discrepancy in detection of fungi between microbiology and histology. Possible reasons include sampling and misinterpretation of contaminants and artifacts on histology. However, this does not appear to completely explain the difference of 7 cases identified by microbiology versus 22 by histologic assessment. Microbial studies are likewise subject to contaminants and technical errors. Although microbiology is necessary for speciating fungi, our results suggest that when given very limited sample, submitting tissue entirely to histology may provide greater yield than microbial studies. Histology also has the advantage of identifying additional findings, e.g. carcinoma, that may be secondarily colonized. A prospective study of a larger series with follow-up, to compare the two methods, is necessary to determine if there is significant advantage or any clinical impact of using one method over the other.
Category: Infections

Wednesday, March 6, 2013 9:30 AM

Poster Session V # 253, Wednesday Morning

 

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