The economic case for investment in the prevention of vertical (mother to child) transmission of HIV and syphilis is easily made – even in low resource settings. Yet the virtual elimination of maternal HIV transmission remains a goal still to be achieved in many regions, while syphilis in pregnant mothers is often unaddressed with tragic consequences in terms of peri-natal mortality.
The final resolution of these problems will no doubt require a multi-dimensional and holistic approach of the kind recommended by the UNAIDS report. Yet a recently trialled technology, designed by biomedical engineers from Columbia University, may ease the way to that solution: it promises to deliver a point-of-care HIV/syphilis test that replicates all the steps of ELISA (enzyme-linked immunosorbent assay), with a sensitivity and specificity to match traditional benchtop assays – but at low cost, with minimal equipment, and requiring no user interpretation (all important considerations in low resource settings).
A recent paper in Nature Medicine describes the technology – the “mChip” assay (mobile microfluidic chip for immunoassay on protein markers), and reports the encouraging results of three trials undertaken in Rwanda.
The device consists in a microfluidic cassette (5.4 cm x 8.5 cm) costing $0.10. A metal spacer, displacing 6 ml of air in a syringe, is used to draw into the cassette a fluid plug consisting in 14 reagents separated by air spacers. The procedure produces a signal that can be detected using low cost optics such as light emitting diodes and photodetectors (costing $0.50 and $6.00 respectively). The test requires less than 1μl of unprocessed whole blood and is complete in 15 minutes.
When tested in Muhima Hospital Kigali on 70 specimens of known HIV status the device demonstrated an overall sensitivity of 100% and a specificity of 96%. It was also evaluated on 101 archived specimens from couples receiving HIV voluntary counselling, and showed similar levels of sensitivity (100%) and specificity (94%). Thirdly, the ability of the device to perform a combined HIV-syphilis test was investigated at Project Ubuzima, using 67 serum and plasma samples collected for a separate research study on female sex workers in Kigali. The duplex test showed sensitivities of 100% and 94% and specificities of 95% and 76% for HIV and syphilis respectively.
A paper covered in a previous blog (Screening for syphilis in pregnancy: evidence for the effectiveness of doing something) reviews the disastrous failure in many low resource contexts to test and treat syphilis in pregnancy. For all the priority rightly given to the prevention of HIV, the inclusion of syphilis in the duplex test seems a commendable element.
Curtis D Chin et al., “Microfluidics-based diagnostics of infectious diseases in the developing world”, Nature Medicine 17, 1015-1019, 31st July 2011