A reliable and easy to transport quality control method for chlamydia and gonorrhoea molecular point of care testing

Abstract

Quality control (QC) is an essential component of point-of-care testing programs. In the context of a randomised-controlled trial (TTANGO) using GeneXpert (Xpert) Chlamydia trachomatis and Neisseria gonorrhoeae (CT/NG) point-of-care testing in remote areas of Australia, we aimed to develop and utilise a stable positive control material. Bacterial cultures of CT and NG were resuspended together to provide cycle threshold (C_t) values of approximately 25 cycles for both CT and NG when tested on the Xpert CT/NG assay. These positive control suspensions were dried in aliquots, heat inactivated, and then provided to 12 participating health services as research-only QC samples in kit form. At each service, a QC sample was resuspended and tested each month on the Xpert. QC results, including Xpert C_t values, were analysed from each site over 30 months and we calculated costs per QC sample. Overall, at 12 health services there were 89 QC samples tested (average of 8 tests per site per year). Mean C_t values for the 89 controls samples were 25.25 cycles (SD = 1.15) for CT, 24.04 cycles (SD = 1.400) for one NG target and 23.35 cycles (SD = 1.55) for the other NG target. No significant differences in C_t value for CT or NG controls were observed over a trial period of 30 months. Positive QC samples for research use in a trial of a molecular point-of-care assay were inexpensive to produce and stable when stored at 2-8°C. For routine use, additional requirements such as meeting National Association of Testing Authority (NATA) regulations and Therapeutic Goods Administration (TGA) approval will need to be achieved.

Keywords: DNA; GeneXpert; assurance; chlamydia; control; gonorrhoea; point-of-care; quality.