1/ Re: Rapid Antigen Tests - Are you confused after today's BC COVID-19 press conference?
Let's take a deeper dive
Let's take a deeper dive
2/ Firstly, it is important to understand that not everyone infected with COVID-19 is infectious (capable of transmitting to others):
BLUE = Infected
RED = Infectious subset
BLUE = Infected
RED = Infectious subset
3/ During the course of an infection, the viral load changes. Most people are infectious for a brief period of time:
https://twitter.com/michaelmina_lab/status/1446944922469388288?s=20
4/ When it comes to rapid antigen tests (RATs) or nucleic acid amplification tests (NAATs), one should not compare them using Sensitivity / Specificity without clarifying the question we are trying to answer, or the problem we are trying to solve.
5/ If you want numbers, here is a nice table from @michaelmina_lab.
Focus on the sensitivity for those who are INFECTIOUS - i.e. what matters when you are trying to reduce transmission).
You can see the RATs are very good at informing us if a person is INFECTIOUS.
Focus on the sensitivity for those who are INFECTIOUS - i.e. what matters when you are trying to reduce transmission).
You can see the RATs are very good at informing us if a person is INFECTIOUS.
6/ Although you can have false positives, 1-3/1000 tests, this can be simply resolved by repeating the RAT and then going for confirmatory PCR if repeat RAT is positive.
7/ Recall that:
a) symptoms do not correlate well with period of infectivity.
AND
b) significant portion of the infectious period occurs during asymptomatic/presymptomatic phases in early infection.
a) symptoms do not correlate well with period of infectivity.
AND
b) significant portion of the infectious period occurs during asymptomatic/presymptomatic phases in early infection.
8/ So to recap, RATs are very good at identifying who is infectious. It does not matter if you are using them for symptomatic or asymptomatic individuals. It does not matter if the individual is vaccinated or not. Focus on the context and the problem.
9/ Now let's shift to yield of testing before "events".
Best time to test is just before the event (Not 48 hrs before or morning of).
This is particularly important if we want to reduce high transmission risk in settings with 3Cs.
#COVIDisAirborne
Best time to test is just before the event (Not 48 hrs before or morning of).
This is particularly important if we want to reduce high transmission risk in settings with 3Cs.
#COVIDisAirborne
10/ The "yield" of testing depends on the GOAL:
#TestToProtect (prevent transmission and outbreaks)
#TestToEnable (enable participation)
#TestToStay (e.g. students in classrooms with outbreaks)
#TestToTreat (identify people early in disease)
#TestToEmpower
#TestToProtect (prevent transmission and outbreaks)
#TestToEnable (enable participation)
#TestToStay (e.g. students in classrooms with outbreaks)
#TestToTreat (identify people early in disease)
#TestToEmpower
11/ RATs are a very useful tool for the above contexts because they are FAST, INEXPENSIVE and ACCESSIBLE (at least the should be for the latter two characteristics)
12/ Now back to the local issue in BC - What "rapid tests" did 🇨🇦purchase?
NB:
Abbott ID Now (an isothermal NAT) and Lucira (a loop-mediated amplification) are molecular tests and NOT rapid Ag tests like the rest on this list.
Lucira can be self performed but they are $$$.
NB:
Abbott ID Now (an isothermal NAT) and Lucira (a loop-mediated amplification) are molecular tests and NOT rapid Ag tests like the rest on this list.
Lucira can be self performed but they are $$$.
13/ What rapid tests did the federal government send to BC?
Only Abbott ID Now (NAAT) requires a "machine"
The RATs on this list do not "require a machine".
BD Veritor has a reader machine but it is not necessary, and the reader contributes to more false positives.
Only Abbott ID Now (NAAT) requires a "machine"
The RATs on this list do not "require a machine".
BD Veritor has a reader machine but it is not necessary, and the reader contributes to more false positives.
14/ So what do the various RATs look like?
Abbott Panbio nasal swab kits come with one buffer bottle so separating them for distribution requires some time. Volunteers can and have done this.
Abbott Panbio nasal swab kits come with one buffer bottle so separating them for distribution requires some time. Volunteers can and have done this.
15/ BD Veritor comes with a reader, but for self testing at home for public health purposes, the reader is not required. The kits can similarly be repackaged for distribution in smaller quantities by volunteers.
16/ We don't have BTNX 5 pack kits in BC but that is not a real barrier for us. We could have used what we had and asked for more (demand will be met with the federal supply; no demand = no supply)
17/ We heard today that we are waiting for the Roche SD Biosensor for distribution. The small advantage is that the buffer tubes are pre-filled so that makes distribution/repackaging kits easier. Again this is not a valid reason for delaying use of existing RATs.
18/ The public can be easily educated on how to perform RATs
This is a sample instructional video we made for @Fraserhealth @EngagedCommuni2 partnership for hot spot RAT distribution. (Translated in different languages)
This is a sample instructional video we made for @Fraserhealth @EngagedCommuni2 partnership for hot spot RAT distribution. (Translated in different languages)
https://twitter.com/VicLeungIDdoc/status/1418648038776532994?s=20
19/ It is also easy for the public to understand the different situations in which RATs are useful (i.e. high yield) for both PREVENTION and CONTROL of outbreaks.
20/ To conclude, it is crucial that we start using RATs now for more situations. We can do this by effectively distributing the Panbio kits that we have. The nasopharyngeal swabs in older NPS kits can be replaced with nasal swabs for distribution.
21/ We are at the start of high risk winter months. The situation is worsened with Omicron VOC transmission. The time to #FreeTheRATs is now.
covid19-sciencetable.ca/sciencebrief/r…
covid19-sciencetable.ca/sciencebrief/r…
22/ For further reading, I would recommend well written, high impact articles by @michaelmina_lab
Rethinking COVID-19 Test Sensitivity
nejm.org/doi/full/10.10…
Rethinking COVID-19 Test Sensitivity
nejm.org/doi/full/10.10…
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