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Background: The diagnostic criterion for gram stain diagnosis of urethritis was lowered from ≥5 polymorphonuclear cells (PMNs) per high power field (HPF) to ≥2PMNs/HPF in the 2015 CDC STD Treatment Guidelines based on data from a single urban sexually transmitted diseases (STD) clinic in Colorado. We sought to 1) quantify the sensitivity, specificity and predictive values of the older criterion (≥5 PMNs/hpf) in our clinic and 2) compare our results with Colorado’s in order to inform our decision to adopt these new guidelines.
Methods: We used clinical data of all men who presented to the Public Health- Seattle & King County (PHSKC) STD clinic for evaluation of new urethral symptoms between January 2001 and December 2014 for this analysis. Receipt of antibiotics ≤1 month prior, known exposure to chlamydia or gonorrhea, or a previous positive test were exclusion criteria. Clinicians report urethral gram stain (GS) result as 0-4 PMNs/hpf, 5-9 PMNs/hpf and ≥10 PMNs/hpf.
Results: 21,925 men presented to the PHSKC STD clinic with urethral symptoms and 19,991 (91%) were included in this analysis. 13,552 had both GS and urethral culture/urine NAAT, of which 14.1% were diagnosed with chlamydia. In our clinic, the old criterion of ≥5 PMNs/hpf had a higher sensitivity, 94.7%, and negative predictive value (NPV), 97.7%, than Colorado’s (sensitivity 83.7%, NPV 91.2%). At PHSKC STD Clinic, 4,636 (23%) gram stains had 0-4 PMNs/hpf; urine NAAT and/or urethral swab culture for chlamydia were obtained from 4,454 (96.1%) of these men, of which 101 (2.3%) were diagnosed with chlamydia infection. In Colorado, chlamydia was found in 8.8% (472/5359) of GS with 0-4 PMNs/hpf.
Conclusions: Use of the new urethritis diagnostic criterion in our clinic only identifies a small number of additional urethral chlamydia infections, a finding that appears to differ geographically. Further validation of the new cut-point is merited.