A direct-to-consumer COVID-19 test available via Amazon with a convenient saliva sample-type and fast central-laboratory processing
The current environment for this third (or is it fourth) wave of COVID-19 SARS-CoV-2 infections is reaching new records. The first week of January 2021 is seeing a 7-day moving average of cases above 234,000 per day (the prior record in mid-July was about 69,000) and the 7-day moving average of deaths is now above 2,800 (the prior record in mid-April was 2,200).
In this backdrop, healthcare workers and first responders in the United States are receiving doses of vaccines; the government had a goal of 20 million doses delivered by the end of December but fell well short of that with an estimated 4 million doses.
The first test available for order via Amazon
In this environment the first COVID-19 test is now available for online order over Amazon; the DxTerity COVID-19 Saliva at-Home Collection Kit with Prepaid Express Return Shipping and Laboratory PCR Testing (yes that is quite a mouthful) was approved last Summer under an FDA Emergency Use Authorization. (Here’s the link to the authorization letter (PDF), a letter for HCPs (PDF), a letter for patients (PDF), and the Instructions for Use (IFU PDF) if you are interested.)
As with other direct-to-consumer tests, before ordering a prescription is required; DxTerity has licensed physician(s) in every state enabling individuals to opt-in for a test via a simple online questionnaire at time of purchases, whether you are symptomatic or asymptomatic, eliminating any hassle of working through their own physician.
A dozen at-home or at-work sample collection tests
There are about a dozen tests approved under EUA for home collection; roughly half are sampled by nasopharyngeal swabs (those long swabs that have to go into a nostril and all the way back until it hits the back of your throat), and half are sampled by saliva.
Saliva has obvious benefits, and earlier over last summer there were conflicting reports whether saliva as a specimen type were actually equivalent in sensitivity and overall test performance compared to swabs, particularly with various episodes of swab and other consumable shortages.
For any test approved under Emergency Use Authorization, the FDA has assembled a convenient chart listing out the different test developers and their respective tests in a chart available here. While not exhaustive, it does include over 100 entries with quantitation data. Table 2c has seven entries for saliva with their NAAT Detectable Units / mL (NAAT stands for Nucleic Acid Amplification Testing), which is the number of molecules detected per mL.
It is noteworthy that there are 117 entries in the table for swabs in transport media (Table 2A), and 4 for direct swabs, for a total of 128 tests for detection of SARS-CoV-2 and their respective Limit of Detection (LoD). The main list of EUA-approved tests (link to the FDA list here) numbers 314 as of this writing in early January. Remember however, only 10 of the tests available are authorized for at-home or at-work sample collection; the vast remainder require a health-care professional to collect the sample and return results.
There are five saliva-based tests with at-home sample collection; a full three of them are from Infinity BiologiX LLC (a spinout from RUDCR, an academic diagnostic laboratory at Rutgers University), one from Phosphorus Diagnostics LLC, and one from P32 Labs LLC.
The DxTerity SARS-CoV-2 RT-PCR test sample collection
A full 30 minutes before the sample is collected, the person being tested must not eat, smoke or drink (even water). As you can see from the illustration, about two mL of saliva is collected in the tube to the fill-line, and the patient simply screws the cap onto the tube releasing the RNAse inactivating and stabilization solution, then inserts the tube into a specimen bag and ships the sample in a provided FedEx UN3373 package.
The DxTerity SARS-CoV-2 RT-PCR test
As an endpoint reverse-transcriptase PCR test run in a central CLIA laboratory, it does not use real-time PCR to get semiquantitative results with monitoring of ongoing fluorescence during amplification; rather the test takes the end-product, and runs that product through a capillary electrophoresis (CE) device. Applied Biosystems (a division of Thermo Fisher Scientific) along with Advanced Analytical (a division of Agilent) has perfected running high current through hair-thin capillaries filled with proprietary polymers for separation of nucleic acid amplification products on the basis of size.
Being naturally high throughput and fast, they can rapidly scale-up the detection at a presumably lower cost. The turnaround time is between 24 and 72 hours, however customer feedback on the Amazon product page indicates many customers receiving their results within 24 hours.
DxTerity SARS-CoV-2 RT-PCR test performance
Their test submission documents show good limit of detection down to 50 copies per mL, competitive with market-leaders Roche and Becton Dickenson. It is notable from the FDA reference panel comparative data (Table 2C) that DxTerity has the best (lowest) LoD of any of the direct-to-consumer saliva tests (Phosphorus is almost 20-times less sensitive).
On the same website they show asymptomatic data from 518 subjects with saliva compared to nasopharyngeal swabs, and show a 513/518 (99.0%) negative asymptomatic concordance; that is they had five false-positives with NP swab negative samples.
Their Percent Positive and Negative Agreement numbers for symptomatic and asymptomatic patients are relatively strong, shown below.
A viable option for employers
Not only does DxTerity offer a single test for at-home use, they offer a 10-pack for employer use, and an online registration process.