Factors Affecting SARS-CoV-2 Test Discordance in Skilled Nursing Facilities.
Amy Recker, Elizabeth M White, Xiaofei Yang and 6 others
PMID 35809634WHAT IT FOUND
In skilled nursing facilities, negative rapid antigen tests were more often followed by positive PCR tests during outbreaks and in symptomatic residents.
Positive antigen tests were rarely followed by negative PCR tests.
Key findings
01Among antigen tests that had a follow-up PCR within 1 day, 9.3% in symptomatic residents and 5.3% in asymptomatic residents were negative antigen followed by positive PCR.
02Among antigen tests that had a follow-up PCR within 1 day, 6.9% during outbreaks and 0.3% outside outbreaks were negative antigen followed by positive PCR.
03Positive antigen followed by negative PCR was rare: 2.1% of antigen tests with a follow-up PCR within 1 day in both symptomatic and asymptomatic residents.
STILL TO COME
How it was doneWhat they foundWhat it means for RNs
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What it does not show
The study could not calculate true false-positive or false-negative rates because most antigen tests did not have a follow-up PCR, and confirmatory PCR was done when clinicians suspected infection or a wrong result. Antigen and follow-up PCR tests were asynchronous, so direct comparison is limited because viral load and antigen expression can change from day to day. Outbreak status was missing for some tests, so the outbreak analysis uses 171,069 antigen tests rather than 171,280. Data ended January 10, 2021, before Delta and Omicron, and when vaccines were just becoming available, so later variants and vaccination may change interpretation. All facilities were from one large provider, Genesis HealthCare, in 23 states, so results may not apply to other nursing home systems. The study was descriptive and did not test whether follow-up PCR or repeat antigen testing improves clinical or infection-control outcomes.
Declared interests
No author conflicts of interest are stated in the supplied text. The publication type notes NIH extramural research support.
The easy way to misread this
Do not read these discordance percentages as true false-negative or false-positive rates. Most antigen tests did not have a follow-up PCR, and PCR was done when clinicians already suspected a wrong result, so the study cannot estimate true test performance.