Diagnostic accuracy of nasopharyngeal swabs in detecting biofilm-producing bacteria in chronic adenoiditis : a preliminary study

Objectives. Biofilms are organized bacterial communities that are playing an increasing role in otolaryngological diseases such as chronic or recurrent middle ear otitis and adenotonsillitis. Various cultural techniques are available to detect biofilm-producing bacteria (BPB), but microbiological analysis of bioptic staining is the reference diagnostic procedure. To our knowledge, the accuracy of nasopharyngeal swabs in diagnosing BPB has never been assessed. Study Design. A prospective study of diagnostic accuracy. Setting. Outpatient clinics of the Departments of Specialist Surgical Sciences and Maternal and Pediatric Sciences, University of Milan, Italy. Subjects and Methods. Forty-two pediatric subjects with chronic adenoiditis (aged 4-18 years) underwent adenoidectomy, during which multiple transoral nasopharyngeal swabs and adenoidal biopsies were performed. BPB were detected by spectrophotometry, and the accuracy of detecting BPB in nasopharyngeal swabs was compared with that of biopsy. Results. BPB were detected in 73.8% of the nasopharyngeal swabs and in 69.1% of the biopsies. The sensitivity and specificity of the nasopharyngeal swabs were, respectively, 75.9% (95% confidence interval [CI], 60.3%-91.4%) and 30.8% (95% CI, 5.7%-55.9%); positive and negative predictive values were, respectively, 71.0% (95% CI, 55.0%-86.9%) and 36.4% (95% CI, 7.9%-64.8%); and the area under the receiver-operating characteristic curve was 0.5 (95% CI, 0.4-0.7). Conclusions. In comparison with biopsy, nasopharyngeal swabs seem to be inaccurate in detecting BPB and should be cautiously used in clinical practice. As these preliminary findings may have been due to the well-known resistance of biofilm to mechanical injuries (such as swab rubbing) or the small study population, they need to be confirmed in larger patient series.