Combination image of scanning electron micrograph of a human T lymphocyte (also called a T cell) from the immune system of a healthy donor and image of an HIV infected H9 T cell. Credit: NIAID

A Dongle For Detecting HIV And Syphilis

Rapid, inexpensive, easy to use point-of-care (POC) diagnostic tests are critically important in stemming infectious diseases, particularly in developing countries. Researchers at Dr. Sam Sia’s Columbia University lab have invented a promising device that can detect both HIV and syphilis and have successfully piloted it in Rwanda.

The Columbia device pairs a microfluidic cassette dongle with a smartphone. Test reagents are preloaded into the cassette. A “one-push” vacuum, like a bulb on an old-fashioned blood pressure cuff, is used to fill the chamber of the cassette with a blood sample, and reduce the need for electricity. Further, the audio jack on a smartphone is used to power the dongle and for data transmission.

Step-by-step illustration of dongle testing. [Credit: Tassaneewan Laksanasopin]

The diagnostic tests were designed for screening, meaning they wanted tests that were very sensitive (would not likely miss cases), even though they might not be very specific (there might be false positive results). The authors state that currently used rapid HIV tests (RDTs) have both a sensitivity and specificity as low as ~85%, though generally better in more controlled settings and with more highly trained personnel. [Note, the cited reference states “a range of 82.4–99.7% (median: 98.1%)]. Thus, up to 15% of cases are missed, and 15% are false positives, under worst conditions.

In the Rwanda field tests, the dongle had a sensitivity of 100% and specificity of 91% for HIV; 77% and 89% for treponemal syphilis; and 80% and 82% for nontreponemal syphilis. (Currently, a non-treponemal RPR or VDRL test is done for screening. These are sensitive, but can have false positives of more than 1%, caused by many infections, including malaria or hepatitis, or in pregnancy, or with connective tissue diseases like lupus.) The treponemal tests are more specific, and used for confirmation, but they can remain positive for life. Using both tests together can reduce the number of people treated unnecessarily or those who would be missed by one alone.

Why this device is important

Sub-Saharan Africa has nearly 70% of the global burden of HIV-infected people, ~25 million in 2012. That year alone, there were (estimated) 1.6 million new HIV infections and 1.2 million AIDS-related deaths, according to UNAIDS. South Africa has the highest incidence (rate of new infections). Often occuring with HIV infections, syphilis accounts for 20-30% of perinatal deaths in Sub-Saharan Africa.

HIV Prevalence in Africa – By derivative work: Louis Waweru Talk HIV_Epidem.png: User:Grcampbell (HIV_Epidem.png) [Public domain], via Wikimedia Commons

This new dongle cassette is useful, as it is capable of testing for HIV and doing both types of testing for syphilis all at the same time, with rapid POC testing. Models suggest that POC testing for syphilis might reduce deaths 10-fold, according to Sia. Early diagnosis of HIV is critical for reducing transmission and for treatment, especially in pregnancy.

The testing technique was easily taught to healthcare workers, and requires only a tiny drop from a finger stick, rather than a larger blood draw from a vein. Testing takes 15 minutes per patient. Specimen handling and transport is minimized, suggesting that this assay will be preferable, if results are confirmed in larger trials.

Surveys found this type of testing was preferred by the patients as being less frightening, less painful, and because of the rapid return of the results.

Other advantages of this system are its cost — $1.44 per triplex test vs. $2.50-$8.50 for conventional testing. Dr. Sia, lead of the Columbia team, estimates producing the dongle to cost only $34, compared to $18,450 for regular reference laboratory ELISA equipment.

The study was funded by Saving Lives at Birth transition grant (USAID, Gates Foundation, Government of Norway, Grand Challenges Canada, and the World Bank) and Wallace H. Coulter Foundation. Work was also done with OPKO diagnostics and the Columbia Mailman School of Public Health, the Rwanda Biomedical Center, and CDC.

For more information: A smartphone dongle for diagnosis of infectious diseases at the point of care