Clinical meanings of rapid serological assay in patients tested for SARS-Co2 RT-PCR

Angelo Virgilio Paradiso; Simona De Summa; Daniela Loconsole; Vito Procacci; Anna Sallustio; Francesca Centrone; Nicola Silvestris; Vito Cafagna; Giuseppe De Palma; Antonio Tufaro; Vito Garrisi; Maria Chironna

The copyright holder for this preprint (which was not peer-reviewed) is the . https://doi.org/10.1101/2020.04.03.20052183 doi: medRxiv preprint All the 191 subjects enrolled in the study had a SARS-CoV-2 RT-PCR test and RapidIgG/IgM test performed. The cohort had a median age of 58.5 years, 60.62% were male and had presented to the Emergency Room at different times from the onset of symptoms. A description of the symptoms wasavailable in 160 of the191 patients. Fourteen subjects (8.7%) were asymptomatic at time the came to the Emergency Room . 70 patients (37%) had positive SARS-CoV-2 RT-PCR tests while 33 (18%) had positive serum IgM/IgGtests. Compared to the RT-PCRtest, the serological test showed an accuracy of 0.67 (95%CI: 0.604-0.741), a sensitivity of 30% and a specificity of 0.89%. Cohen's Kappa value was 0.21, whose strength of agreement, according to Altman (10) was considered "Fair". Notably,13 patients (7%) had positiveserological testsbut negative RT-PCRresult. The distribution of the percentage of positive results detected by both tests broken down by days from symptom onset is shown in Figure 1 . Aclear increase inpositive serological tests can be observed as more days elapsed from symptom appearance, reaching 66.67% 15 days after symptom onset. Conversely, the highest likelihood of a positive RT-PCR test resultwas seen9-10 days from symptom onset and it decreased after that point in time. Amongstthe asymptomatic individuals,28.57% had positive RT-PCR test result while21.43% had serological test one. A further analysis regardingthe behavior of IgM and IgGaccording to the time from symptom onset is described in Figure 2 . Only minimal differences in the behavior of the two immunoglobulins with respect tothe time of symptom appearance became evident. However, all 13 patients withVivaDiag TM positive test and negative RT-PCR result (6.8%) were positive for IgM while only 7 subjects resulted positive for IgG. Univariate and multivariate logistic regressions were performedto look for independent variables predictive of positive VivaDiag TM and RT-PCR test results (Table 2 ).Both univariate and multivariate analysesshowed that age>58.5years and more than 15 days from symptom onset were significantly associated with VivaDiag TM positivity while 9-10 days after symptom onset was related to positive RT-PCR test result.