External quality assessment for yaws elimination in low- and middle-income countries using plasmid-based proficiency...

We aimed to establish an external quality assessment (EQA) programme for the yaws eradication campaign that would meet the needs of reference and district-level laboratories in low- and middle-income countries.

We designed proficiency testing items (PTIs) using a plasmid containing gene target sequences for Treponema pallidum (TP) and Haemophilus ducreyi (HD). The storage stability of the plasmids under different environmental conditions was then tested. A proficiency testing panel of seven swabs loaded with different concentrations of plasmids in different combinations, as well as human HEK293 cells to simulate the sample background, was prepared and sent to participating reference (RL) and district (DL) laboratories in Ghana, Côte d'Ivoire and Cameroon followed by three rounds of blinded proficiency testing. We tested quantitative real-time PCR (qPCR) performance of reference laboratories and loop-mediated isothermal amplification (LAMP) performance of district laboratories and retested 20% of human field samples at the London School of Hygiene & Tropical Medicine laboratories to further assess qPCR quality.

PTIs proved to be stable in dry conditions with no significant loss of copy number. Participating laboratories achieved qPCR results with a concordance of 95.0-100.0% (97.7% ± 5.2% (mean±standard deviation ((SD)) with the provider and a concordance of 76.0-100.0% (TP: 90.3 ± 13.7% and HD: 78.5 ± 7.5% (mean±SD)) for LAMP results, with inconsistencies, particularly in the detection of low HD plasmid DNA levels combined with high TP plasmid copies. Retesting of field samples resulted in 100% correct TP and HD sample identification by the African reference laboratories.

We have developed a functional plasmid-based EQA programme specifically designed to meet the needs of resource-poor settings in the tropics. The programme is suitable as a blueprint for other disease programmes.