Zhang H¹, Varadhan H¹

¹Microbiology Department, NSW Health Pathology Hunter

Introduction:

16s rRNA polymerase chain reaction (PCR) is a valuable tool for identifying pathogens in culture-negative specimens¹. However, its high cost necessitates careful selection of appropriate samples. This retrospective study aimed to identify factors associated with positive 16s PCR results.

 

We reviewed all 16s PCR requests through our regional Australian laboratory from 2019-2023, that were sent for reference testing. Variables examined included specimen type and location, culture and microscopy findings including leukocytes and Gram stain, and 16s PCR results. Blood cultures and specimens sent for organism identification rather than pathogen detection were excluded.

 

591 specimens in total were analysed. 16s PCR was positive in 117 (19.8%), with invasive respiratory samples yielding the highest positivity rate (40.6%). Leukocytes were seen on microscopy in 72.6% of 16s PCR positive samples compared to 63.7% in negative samples; while not statistically significant (p=0.07), limiting testing to this would have reduced testing volume by 34.5%. Most positive 16s PCR specimens had no organisms seen in Gram stain (86.3%).

 

Predictors of 16s PCR positivity included invasive respiratory specimens and leukocyte presence in microscopy, however the latter was not statistically significant. Negative Gram stain did not preclude 16s PCR positivity. Further analysis is required.

 

1. Janda JM, Abbott SL. 16S rRNA gene sequencing for bacterial identification in the diagnostic laboratory: pluses, perils, and pitfalls. J Clin Microbiol. 2007;45(9):2761-4.