This study showed that POC-testing using the eazyplex STD complete platform resulted in good sensitivity for N. gonorrhoeae (75–100%), C. trachomatis (77–88%), as well as M. hominis (83–86%) and excellent specificity (≥ 97%) compared to the reference central-laboratory-based diagnostic methods.
In our study sensitivity differed depending on sample site and pathogen, whereas specificity was excellent overall. Sensitivity for C. trachomatis was similar in urethral and anal samples (80% and 88%, respectively), in 3/5 false negative samples bacterial load was low with cycle threshold values of ≥ 30 by the reference PCR method. For N. gonorrhoeae sensitivity was higher among urethral than anal samples (100% vs. 75%). Likewise, sensitivity for detection of U. urealyticum was excellent for urethral samples, but only modest for anal samples (100% vs. 61%). However, in this case the reference PCR test method used by the clinical microbiology laboratory at the time did not differentiate between Ureaplasma spp., therefore the potential presence of U. parvum would have led to an underestimation of sensitivity for U. urealyticum. A higher frequency of U. parvum on the anal mucosa compared to the urethra could therefore be responsible for at least part of the observed difference. There were too few positive pharyngeal samples to perform meaningful calculations with respect to sensitivity for this bodysite.
Novel POC test systems using loop-mediated amplification have increasingly been introduced in the last years for different infectious agents, e.g. for malaria in pregnant women [5], SARS-CoV-2 [6], or C. trachomatis [7]. With a rising incidence of STI the need of POC tests has increased for this indication with accuracy and reasonable pricing being main factors required for implementation [8]. Already in 1999 a study demonstrated that a rapid test for C. trachomatis with a modest sensitivity of 63% resulted in treatment of more cases of infection than following conventional PCR testing, if the proportion of patients returning was less than 65% [9]. Thus, POC rapid testing can be a good alternative in situations when patients may not return to the clinic for a second visit. Being able to receive appropriate treatment almost immediately after diagnostic sampling was considered a valuable advantage by the majority of participants during the second phase of our study, both with respect to symptom relief and protection of future contact persons.
In addition to rapid results within about 30 minutes as well as good sensitivity and excellent specificity the STD complete platform also meets other ASSURED criteria [10] developed by the World Health Organization, qualifying it for use even in resource limited settings: it is user-friendly allowing for operation after minimal training, equipment-free as a stand-alone platform, robust with no need for refrigeration, and as a small, portable device can be easily delivered to the end user.
An obvious limitation of our study was the single center setting. However, baseline characteristics of the study participants and testing indications correspond well with the typical setting of MSM outpatient STI-testing in Germany. In addition, the number of samples allowed for robust analysis of sensitivity and specificity for urethral and anal sampling sites. Reference testing by the clinical microbiology laboratory at the time somewhat limits our conclusions to mainly N. gonorrhoeae and C. trachomatis. However, even the potentially underestimated sensitivity for testing of U. urealyticum in anal samples is still in the range of clinical usefulness compared to routine testing requiring a follow-up appointment. While STD-complete included testing for M. genitalium, again reference testing at the time only allowed for calculation of test characteristics for M. hominis, which is less clinically relevant. If results for M. hominis were used as indication for test characteristics with respect to M. genitalium, clinical usefulness can be assumed for this pathogen also.
In conclusion, our study demonstrated that the eazyplex STD complete platform is a useful rapid diagnostic method for POC STI-testing especially for N. gonorrhoeae and C. trachomatis. In addition to good sensitivity and excellent specificity it offers the clinical benefit of almost immediate treatment initiation.