Table 3

Cross tabulation of results of the triage algorithm with and without FebriDx as well as the results of FebriDx within the possible COVID-19 group compared with a SARS-CoV-2 RT-PCR reference standard

A		SARS-CoV-2 RT-PCR
A		Positive	Negative	Total
Clinical criteria alone (without FebriDx) (n=3433)	Likely or possible COVID-19	130	1270	1400	PPV:
					9.3%
					(95% CI 7.9 to 10.9)
	Unlikely COVID-19	6	2027	2033	NPV:
					99.7%
					(95% CI 99.3 to 99.9)
	Total	136	3297	3433
		Sensitivity	Specificity
		96%	61.5%
		(95% CI 91 to 98)	(95% CI59.8 to 63.1)

B		SARS-CoV-2 RT-PCR
B		Positive	Negative	Total
FebriDx alone in the possible COVID-19 group with FebriDx done (n=958)	FebriDx positive	41	91	132	PPV:
					31%
					(95% CI 24 to 39)
	FebriDx negative	4	822	826	NPV:
					99.5%
					(95% CI 98.7 to 99.8)
	Total	45	913	958
		Sensitivity	Specificity
		91%	90.0%
		(95% CI 78 to 97)	(95% CI 87.9 to 91.8)

C		SARS-CoV-2 RT-PCR
C		Positive	Negative	Total
Triage algorithm using clinical criteria and FebriDx (n=3433)	Triage positive	126	448	574	PPV:
					22%
					(95% CI 19 to 26)
	Triage negative	10	2849	2859	NPV:
					99.7%
					(95% CI 99.4 to 99.8)
	Total	136	3297	3433
		Sensitivity	Specificity
		93%	86.4%
		(95% CI 87 to 96)	(95% CI 85.2 to 87.5)

Measures of diagnostic performance are presented for the triage algorithm for the detection of COVID-19: (3A) using clinical criteria alone without FebriDx, where subjects are classified as positive or negative based on clinical criteria shown in table 1. Subjects were ‘positive’ if they were assigned as likely or possible COVID-19 based on clinical criteria alone. (3B) Using the FebriDx assay alone within the possible COVID-19 group receiving a FebriDx test. Subjects are classed as FebriDx positive or negative based on the FebriDx test only. (3C) Using clinical criteria supported by the FebriDx assay. Subjects were classed as triage positive or negative based on their flow through the algorithm as shown in figure 1. Patients were triage positive if they were triaged as likely COVID-19 or possible COVID-19 without a negative FebriDx result. Patients were triage negative if they were triaged as unlikely COVID-19 or possible COVID-19 with a negative FebriDx result.
NPV, negative predictive value; PPV, positive predictive value.