As a retired internist and gerontologist, I have closely followed our government’s efforts to help us identify HCP (Health Care Personnel) with SARS-CoV-2 with the goal of reducing the risk of its transmission to residents in our homes.   Early on, we had significant difficulties obtaining the materials for molecular (RT-PCR) testing and later had difficulties obtaining the results within the desired 48-hour TAT (Turn Around Time).  However, in the past several months many facilities in our state have been able to obtain at least this TAT on their mandatory weekly screening of their HCP.

Antigen- (Ag-) based POC testing initially appeared to be a viable alternative to quickly identify symptomatic HCP with positive tests having high positive predictive values for both the Quidel Sophia 2 and the Abbott BD Veritor, when used in symptomatic persons.   Many SNFs have now received these free machines and initial test cartridges from HHS.  They require a CLIA waiver, are only authorized by EUA (Emergency Use Authorization) for symptomatic HCP, and cost about $ 25-35 dollar per cartridge.  

On Aug 26, the FDA approved the new Abbott BinaxNOW antigen test (see link).  CMS purchased a starter supply to distribute to 7,600 high-risk nursing homes.  A few of the facilities in my community have received this starter kit and have questions about the utility of this test.  In the FDA EUA, the test reports a 97.1% positive agreement with RT-PCR testing and a 98.5% negative agreement.    This test doesn’t require a machine, costs $5 per test, and can be done on a more tolerable mid-turbinate swab, which may be self-collected.  The test is similar to OTC pregnancy test kits with color test results expected within 15 minutes.  

The BinaxNOW EUA is only for use within 7 days of symptom onset compared to 5 days for BD Veritor and 12 days for Lumira DX.  This in large part reflects the observation that the test requires enough SARS-CoV-2 antigen to be present to become positive.  From well-done studies in Singapore earlier this year, we know that peak antigen levels occur about day 4- 5 from onset of infection and are highest the day prior to onset of symptoms (if symptoms develop) and then quickly taper off by day 7 from symptom onset.   If a test is done too soon before onset of symptoms, the antigen levels could be too low, yielding a false negative result.

Because of this, the CDC has recommended that the Ag POC tests only be done on symptomatic patients, as long as a facility has reliable access to RT-PCR test results in < 24-48 hrs.  Using this model, HCP are pulled from work if they become symptomatic pending results of the RT-PCR test.  The downside of the more reliable PCR test is its requirement for full PPE for specimen collection, a test TAT of 24-48 hours, and collection of nasopharyngeal specimens on a weekly basis, which are commonly painful.  Some facilities have noticed increased staff refusals for nasopharyngeal specimen collection, which have aggravated their staffing problems and ability to take new admissions.  

The Wall Street Journal published an article in which the author proposed using POC testing as a screening tool for HCP, but testing twice a week.  This would likely identify early false negative results not detected by weekly POC Ag testing, and remove asymptomatic workers from the facility sooner than weekly RT-PCR testing.  At a cost of $ 5 per test, this would be financially feasible and may have advantages noted above in comparison to RT-PCR testing.  

I hope that Abbott labs or a research organization will conduct a non-inferiority study in the nursing home setting comparing twice or thrice weekly POC BinaxNOW POC testing with the required weekly RT-PCR testing.  I have sent this proposal to a Medical Director of a large CCRC in our state, who agrees that such a study could be very valuable.  In our Sonoma and Marin County SNF Learning Collaborative, an ID specialist has even proposed assessing the value of daily testing.

With the winter surge already starting in other parts of our country, the time is now to optimize our ability to detect asymptomatic HCP earlier and further reduce their risk of transmitting SARS-CoV-2 from our HCP and contract on-site workers to our residents. 

I provided vacation relief during the recent wildfire evacuations of September 28 for my former CCRC.  Though residents had been quickly evacuated and sent to multiple sites, none has subsequently developed COVID.  We did test our 450 asymptomatic residents with BinaxNOW and had no + cases.  The 2 equivocal cases proved negative on RT PCR testing.  

I just received a powerpoint presentation given by Dr. S. Todd Stolp to our SNF collaborative.  The main focus is on the details of how BinaxNow might be used in the future.