EVALUATION OF A RAPID ANTIGEN TEST FOR SARS-COV-2 IN SYMPTOMATIC PATIENTS AND THEIR CONTACTS: A MULTICENTER STUDY

BACKGROUND

Point-of-care rapid tests to identify SARS-CoV-2 can be of great help because, in principle, they allow decisions to be made at the site of care for treatment, or for the separation of cohorts avoiding cross-infection, especially in emergency situations.

METHODS

A cross sectional study in adults requesting care in Emergency Rooms (ER), or the outpatient clinics of referral hospitals for COVID-19, to define the diagnostic characteristics of a rapid antigen test for SARS-CoV-2 (the Abbott Panbio™) having as a gold standard the RT-PCR for SARS-CoV-2. Health personnel in a routine situation within an active pandemic in several cities of Mexico performed the tests.

RESULTS

A total of 1,069 participants with a mean age of 47 years (SD 16 years), 47% with a self-reported comorbidity, and an overall prevalence of a positive RT-PCR test of 45%, were recruited from eight hospitals in Mexico. Overall sensitivity of the Panbio test was 54.4% (95%CI 51-57) with a positive likelihood ratio of 35.7, a negative likelihood ratio of 0.46 and a Receiver-Operating Characteristics curve area of 0.77.

Positivity for the rapid test depended strongly on an estimate of the viral load (Cycle threshold of RT-PCR, Ct), and the days of symptoms. With a Ct≤25, sensitivity of the rapid test was 0.82 (95%CI, 0.76-0.87). For patients during the first week of symptoms sensitivity was 69.6% (95%CI 66-73). On the other hand, specificity of the rapid test was above 97.8% in all groups.

CONCLUSIONS

The Panbio™ rapid antigen test for SARS-CoV-2 has a good specificity, but due to low and heterogeneous sensitivity in real life, a negative test in a person with suggestive symptoms at a time of community transmission of SARS-CoV-2 requires confirmation with RT-PCR, and after the first week of symptoms, sensitivity decreases considerably.