• Mauro Maniscalco, Pasquale Ambrosino, Anna Ciullo, Salvatore Fuschillo, Valerio Valente, Carlo Gaudiosi, Debora Paris, Raffaele Cobuccio, Francesco Stefanelli, and Andrea Motta.
• Istituti Clinici Scientifici Maugeri IRCCS, 27100 Pavia, Italy.
• Sensors (Basel). 2021 Aug 25; 21 (17).

BackgroundThe standard test that identifies the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is based on reverse transcriptase-polymerase chain reaction (RT-PCR) from nasopharyngeal (NP) swab specimens. We compared the accuracy of a rapid antigen detection test using exhaled breath condensate by a modified Inflammacheck® device with the standard RT-PCR to diagnose SARS-CoV-2 infection.MethodsWe performed a manufacturer-independent, cross-sectional, diagnostic accuracy study involving two Italian hospitals. Sensitivity, specificity, positive (PLR) and negative likelihood ratio (NLR), positive (PPV) and negative predictive value (NPV) and diagnostic accuracy with 95% confidence intervals (95% CI) of Inflammacheck® were calculated using the RT-PCR results as the standard. Further RT-PCR tests were conducted on NP specimens from test positive subjects to obtain the Ct (cycle threshold) values as indicative evidence of the viral load.ResultsA total of 105 individuals (41 females, 39.0%; 64 males, 61.0%; mean age: 58.4 years) were included in the final analysis, with the RT-PCR being positive in 13 (12.4%) and negative in 92 (87.6%). The agreement between the two methods was 98.1%, with a Cohen's κ score of 0.91 (95% CI: 0.79-1.00). The overall sensitivity and specificity of the Inflammacheck® were 92.3% (95% CI: 64.0%-99.8%) and 98.9% (95% CI: 94.1%-100%), respectively, with a PLR of 84.9 (95% CI: 12.0-600.3) and a NLR of 0.08 (95% CI: 0.01-0.51). Considering a 12.4% disease prevalence in the study cohort, the PPV was 92.3% (95% CI: 62.9%-98.8%) and the NPV was 98.9% (95% CI: 93.3%-99.8%), with an overall accuracy of 98.1% (95% CI: 93.3%-99.8%). The Fagan's nomogram substantially confirmed the clinical applicability of the test in a realistic scenario with a pre-test probability set at 4%. Ct values obtained for the positive test subjects by means of the RT-PCR were normally distributed between 26 and 38 cycles, corresponding to viral loads from light (38 cycles) to high (26 cycles). The single false negative record had a Ct value of 33, which was close to the mean of the cohort (32.5 cycles).ConclusionsThe modified Inflammacheck® device may be a rapid, non-demanding and cost-effective method for SARS-CoV-2 detection. This device may be used for routine practice in different healthcare settings (community, hospital, rehabilitation).

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