Validation of a new testing algorithm for syphilis in a small developing country

Abstract

Objective

To evaluate new test kits and a reverse algorithm for the diagnosis of syphilis

at the Queen’s Park Counselling Centre and Clinic (QPCC&C), the national

reference laboratory in Trinidad and Tobago, to determine feasibility for

implementation.

Methods

The diagnostic testing for syphilis in Trinidad and Tobago involved the use of

the traditional algorithm. The QPCC&C in collaboration with the Centers for

Disease Control and Prevention STI & International Laboratory Branches

(CDC-STI), Atlanta, developed a reverse diagnostic syphilis algorithm that

allows specimens to be screened with a treponemal test (ELISA) and non

reactive samples are reported as negative for syphilis. ELISA reactive

specimens were reflexively screened with the quantitative VDRL test to

detect present or past treated exposure to syphilis. Samples with discordant

test results were subsequently screened using the Treponema Pallidum

Particle Agglutination (TPPA) as a confirmatory test. To validate the

algorithm, 5mls of blood from 40 high risk HIV and STI patients in Trinidad

were obtained, the sera separated and split equally to allow for the simultaneous testing and review of results

using the reverse testing algorithm at both the QPCC&C and CDC STI laboratories. Ethical approval was

granted for this process by the Ministry of Health, Trinidad and Tobago.

Results

The results obtained showed 100% concordance between laboratories which resulted in the validation of the

algorithm.

Conclusion

The validation of these test kits and reverse algorithm will allow the national STI reference laboratory to

increase its throughput and offer an improved service to the population.