A new diagnostic tool, called STD Direct Flow Chip Kit (Master Diagnóstica, Granada, Spain), is cost- and time-saving for identifying sexually transmitted disease (STD) pathogens and can analyze a wide variety of clinical specimens avoiding the DNA extraction step, according to a study published in the European Journal of Clinical Microbiology & Infectious Diseases.

STD Direct Flow Chip Kit is a qualitative molecular diagnostic test based on multiplex polymerase chain reaction (PCR) and automatic hybridization onto a macroarray with specific oligo probes. It allows for the simultaneous detection of 9 different species of STD pathogens: Chlamydia trachomatis (serovars A-K and L1-L3), Haemophilus ducreyi, herpes simplex virus (types 1 and 2), Mycoplasma genitalium, Mycoplasma hominis, Neisseria gonorrhoeae, Treponema pallidum, Trichomonas vaginalis, and Ureaplasma (U urealyticum/U parvum).

To evaluate its clinical performance, researchers compared the diagnostic performance of this kit with the Anyplex™ II STI-7 Detection Kit (Seegene, Seoul, Korea), which can detect 7 pathogens causing STDs (C trachomatis, N gonorrhoeae, T vaginalis, M genitalium, M hominis, U urealyticum, and U parvum).

The clinical performance of STD Direct Flow Chip Kit was evaluated at 2 different stages, using the Anyplex II STI-7 Detection Kit as the reference method. First, the performance of the STD Direct Flow Chip Kit was evaluated from purified DNA of 358 clinical specimens, previously characterized as STD-positive (n=302) and STD-negative (n=56), using the reference method. Once the clinical validation from purified DNA was completed, researchers assessed the performance of the STD Direct Flow Chip Kit with direct testing of clinical specimens (n=633), without the initial nucleic acid extraction step. Six different clinical specimens were included in the validation: urine, semen, urethral, pharyngeal, endocervical, and perianal swabs. Any discordances were resolved using either a third molecular assay or DNA sequencing.

In the first stage, the sensitivity and specificity were 99.45% and 100%, respectively, and an agreement of 99% (kappa index, 0.969; 95% CI, 0.934-1.004). Similarly, in the second stage, analysis of clinical specimens by direct PCR showed a sensitivity and specificity of 98.06% and 99.88%, respectively, and an agreement of 98% (kappa index, 0.954; 95% CI, 0.930-0.978).

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The researchers noted the inclusion of M hominis, U urealyticum, and U parvum in the STD Direct Flow Chip Kit as a limitation, because these are human commensals whose role in developing STDs is still controversial. They noted that detecting and treating these pathogens could provoke unnecessary antimicrobial resistance.

The STD Direct Flow Chip Kit “constitutes a promising alternative to routine procedures in diagnosis,” noted the researchers. The kit is easy to use, and “the interpretation of results quick, leading to diagnosis in less than 4 h[ours],” they concluded.

Reference

Barrientos-Durán A, de Salazar A, Alvarez-Estévez M, Fuentes-López A, Espadafor B, Garcia F. Detection of sexually transmitted disease-causing pathogens from direct clinical specimens with the multiplex PCR-based STD Direct Flow Chip Kit. Eur J Clin Microbiol Infect Dis. 2020;39(2):235-241.