#CovidToday for #Delhi
Delhi has 3x its testing capacity from 6000 to 18000 tests per day. 👏 However, most of this increase comes from the new rapid antigen tests, which have much lower sensitivity. This has important implications.
A thread analyzing Delhi’s testing..
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Delhi has 3x its testing capacity from 6000 to 18000 tests per day. 👏 However, most of this increase comes from the new rapid antigen tests, which have much lower sensitivity. This has important implications.
A thread analyzing Delhi’s testing..
1/n
The rapid ag test has a sensitivity of 50-84% (image, ICMR). Even if we assume it to be 70%, and considering this sens is calculated by comparing to RTPCR, it is 30% lower than the earlier done 6000 PCR/day.
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As in first chart, positivity rate has declined. However this decline would be partly because the new 12000 rapid ag tests are not simply not as good at picking up positives as the RTPCR.
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Still, this testing expansion is a highly welcome and much needed move. An advantage is that results come within an hour, so the delay for followup action (isolation, contact tracing) is reduced. 3-10 days for PCR vs 1 hour for rapid test.
timesofindia.indiatimes.com/city/delhi/del…
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timesofindia.indiatimes.com/city/delhi/del…
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These rapid ag tests are being used mainly in containment zones, which is a good step since using it in high prevalence areas will increase the yield, considering the low sensitivity. Example..
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Containment zone : assume a prevalence of 10%, about 93 out of every 100 rapid tests will be neg and require followup PCR.
Low prev community: a prev of 2% will give you 99 rapid tests coming back neg and needing PCR. A very low yield!
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Low prev community: a prev of 2% will give you 99 rapid tests coming back neg and needing PCR. A very low yield!
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Some have suggested using pooled samples in PCR to retest the rapid test negatives to preserve resources. Now pooling works only when prevalence is low, below 2%. Lets see if pooling is feasible in this scenario.
covid.aiims.edu/pooled-sample-…
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covid.aiims.edu/pooled-sample-…
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Lets say above 93 rapid test negatives in the containment zone undergo followup PCR. 3 out of these 93 negatives are actually positive but were missed by rapid test. So PCR sample pool prevalence is 3/93= 3.2%, above the optimal limit for pooling.
Maybe pooling wont work.
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Maybe pooling wont work.
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So, it is important to ensure that PCR capacity is parallely ramped up, and a false comfort is not taken in having tripled the testing by rapid tests. PCR is the gold std and can be used in any setting, including to detect resurgence in community— important!
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If rapid ag kits could be worked upon to inc sensitivity, it would solve many testing woes in the country!
Rapid testing is point of care, and requires much less manpower, training, money, transport and effort to ramp up than RTPCR. Also, obliiterates the testing delay!
fin.
Rapid testing is point of care, and requires much less manpower, training, money, transport and effort to ramp up than RTPCR. Also, obliiterates the testing delay!
fin.
covidtoday.in tracks each state in multiple relevant epidemiological indicators, showing transmission and testing.
Each state needs a hand-crafted COVID-19 response.
@ashishkjha trying to track metrics that matter.
Each state needs a hand-crafted COVID-19 response.
@ashishkjha trying to track metrics that matter.
