Swab, Aspirate, or Biopsy? A Retrospective Comparison of Microbial Yield and Concordance in Suspected Pyogenic Infections.

Introduction: Early and accurate diagnosis of pyogenic infections is essential to guide treatment and prevent complications like bacteremia, endocarditis, and death. Debate and controversy continue regarding the optimal specimen for microbiological diagnosis of pyogenic infections in emergency settings. Therefore, this study was conducted to evaluate concordance in the microbial yields obtained from the three techniques of sampling, i.e., pus swab, pus aspirate, and tissue biopsy. Materials and Methods: A total of 363 paired samples (swab and aspirate, swab and biopsy, aspirate and biopsy) from the same patient and site of infection received over one year were analyzed, retrospectively. Microbial yields, mixed bacterial growth, and contamination rates were compared among the three sample types. Results: Tissue biopsies consistently provided the highest microbiological yield, outperforming both swabs (54.2% vs. 34.6%) and aspirates (43.8% vs. 38.5%). This difference in the diagnostic yield for paired tissue biopsy and swab samples was statistically significant (p value = 0.0038). Swabs exhibited high false negative rates (23.4%). The highest concordance was observed between tissue biopsy and aspirate (73.9%), indicating better reliability of these samples over swabs, which are superficial in nature. Conclusions: Tissue biopsies demonstrate the highest diagnostic yield for pyogenic infections, reinforcing their role as the gold standard. Pus aspirates offer a reliable alternative for less invasive sampling, while swabs are limited by their high false negative rates and inability to differentiate between colonizers and pathogens. In conclusion, employing appropriate sampling techniques based on the infection site can significantly enhance diagnostic precision and optimize patient care in emergency settings.