Prospective evaluation of non-invasive saliva specimens for the diagnosis of syphilis and molecular surveillance of <i>Treponema pallidum</i>

The promising diagnostic performance of molecular testing for syphilis using saliva and urine samples has been reported; however, further evaluation of its possible application for diagnosis and molecular surveillance is required. In addition, the development of a rapid and easy-to-perform molecular test for syphilis is important for its use in the clinical setting. We comprehensively evaluated the diagnostic and surveillance performance of two novel loop-mediated isothermal amplification (LAMP) assays using saliva and urine samples. Saliva, urine, and whole blood were collected from patients who underwent serological testing for syphilis at outpatient clinics. <i>Treponema pallidum</i> DNA in specimens was detected using quantitative PCR (qPCR), nested PCR, and novel LAMP assays. <i>T. pallidum</i> genotyping was conducted by multi-locus sequence typing (MLST). Of the 163 patients recruited, 98 were diagnosed with syphilis (primary: <i>n</i> = 35; secondary: <i>n</i> = 40; latent: <i>n</i> = 23). qPCR showed the highest sensitivity among the molecular tests performed with a sensitivity of 54.1% and 30.3% for all syphilis patients using saliva and urine samples, respectively. A novel method of LAMP combined with dry reagents and crude DNA extraction (Dry-LAMP) showed a probit detection limit of 37.4 copies/reaction within 45 min. The agreement rate between Dry-LAMP and qPCR for saliva was 95.7% (<i>κ</i> coefficient 0.90). The <i>T. pallidum</i> genotype was identified in 48 patients by MLST using saliva samples. Molecular analysis of saliva could be used as a supplementary diagnostic test for syphilis and molecular surveillance of the <i>T. pallidum</i> genotype. Dry-LAMP is expected to be helpful in the clinical diagnosis of syphilis.