Experience with Panbio™ rapid antigens test device for the detection of SARS-CoV-2 in nursing homes

Since the beginning of the COVID-19 pandemic, viral RNA detection using reverse transcriptase polymerase chain reaction (PCR) has been used as a diagnostic test for the SARS-CoV-2 virus.^1,2 The main limitation of this is that its results are not immediate, which lengthens decision-making in the event of possible outbreaks.³ This limitation is especially important in the context of care homes, where the great vulnerability of their residents makes the early implementation of measures essential for controlling the spread of the virus.⁴

In September, new diagnostic tests (rapid antigen detection tests) began to be marketed in Spain, which provide a rapid diagnosis in 15–20 min in the healthcare setting, with a simple, low-cost procedure.^1,3 They present a sensitivity greater than 90% and a specificity greater than 95% in patients with symptoms of less than seven days evolution.³

Given the arrival of these tests, our care home coordination and support unit decided to test their usefulness during the month of September and compare their reliability and agreement with the PCR test. To do this, residents who presented symptoms compatible with COVID-19 and/or were close contacts of residents with a positive COVID-19 diagnosis were given a PCR test and simultaneously a rapid antigen detection test (Panbio™ COVID-19 Ag Rapid Test Device).

Both tests were used in 30 residents, with a mean age of 76.23 years (SD: 19.76). Of these, 36.67% were male and 63.33% female. In total, 90% had had symptoms compatible with SARS-CoV-2 infection for less than five days and the other 10% were asymptomatic, but were close contacts.

The rapid tests detected 19 positive and 11 negative cases while the PCR test detected 20 positive cases (9 cases with Ct below 20, 8 cases with Ct between 20 and 25, and the other 3 cases with Ct above 25) and 10 negative cases (Table 1). The agreement between the PCR and the antigen test was 96.66%.

Table 1.

Rapid antigen test for detection of SARS-CoV-2 compared to RT-PCR.

		RT-PCR		Total
		Positive	Negative
Panbio™ COVID Ag	Positive	19	0	19
	Negative	1	10	11
Total		20	10	30

RT-PCR: reverse transcription polymerase chain reaction.

If we analyse the agreement according to the reason for conducting the test, it was 100% when they were used in symptomatic residents, while the only case in which the results of the tests differed was when it was used in an asymptomatic close contact. In this case, the antigen test result was negative while the PCR was positive in two genes at Ct amplification thresholds of 29.8 and 39.7.

The sensitivity of the test was 95% and the specificity 100%. The positive predictive value was 100% and the negative predictive value was 90.9%.

Our first contact with antigen tests reveals their usefulness as a diagnostic test for COVID-19, as the Ministry recognised on 25 September.³ Agreement with the PCR test in this study was almost 100%, being at its maximum when the resident presented compatible symptoms. Most authors highlight a greater sensitivity of antigen tests when the viral load is high,^5,6 especially when Ct values are less than or equal to 25,¹ a fact that our study confirms. The viral load was high in most cases in which the antigen test was positive. Furthermore, in the only discordant case, the PCR showed a low viral load.

One of the main advantages of using this test in care homes is the possibility of being able to perform them at the residents’ point of care, obtaining the result in 15 min and thus allowing early decision-making and isolation. In addition, the simplicity of these tests makes it possible for the nursing staff of the care homes to perform the tests themselves, thus speeding up diagnosis.

In conclusion, the experience presented here shows a new way of diagnosing the SARS-CoV-2 virus that is of special interest for residential care homes, thus following the trend of other authors who accept the use of tests that are less sensitive but rapid, and with a lower cost.^7,8 Its use allows early diagnosis and consequently a decrease in the spread of the virus and its consequences in this vulnerable population.