Comparison of serologic and molecular SARS-CoV 2 results in a large cohort in Southern Tuscany demonstrates a role for serologic testing to increase diagnostic sensitivity

Pancrazzi, Alessandro; Magliocca, Pasqualino; Lorubbio, Maria; Vaggelli, Guendalina; Galano, Angelo; Mafucci, Manuela; Duranti, Diletta; Cortesi, Monica; Mazzeschi, Erica; Fabbroni, Sara; Viti, Gianluca; Tartaglia Polcini, Alessandro; Tripodo, Emanuela; Sanchini, Paola; Gervino, Silvana; Tacconi, Danilo; Dei, Simona; Mazzierli, Monica; D'Urso, Antonio; Ognibene, Agostino

BACKGROUND: Since February 2019, Italian hospitals registered COVID-19 (COronaVIrus Disease 19) cases more often than the rest of the country. During this epidemic, health authorities requested swab tests, whileseeking new patient paths. METHODS: A dual laboratory approach was evaluated, consisting ofpatient care reports for viral RNA detection on swabs and rapid serological tests in 516 patients (192 symptomatic or paucisymptomatic and 324 asymptomatic). RESULTS: We found the molecular positive fraction equal to 12% (23/192) among symptomatic/paucisymptomatic (S/P) and 15.4% (50/324) in asymptomatic (As) sets. Among subsets, we observed serologically positive results, corresponding to 35% (8/23) for S/P and 38% (19/50) for As. Among molecular negative cases, we detected specific Immunoglobulin G or M (Ig G or Ig M) positivity in the S/P cohort equal to 6.6% (11/167) and 6% (15/246) in As cases. For indeterminate molecular results, we found S/P serological positivity equal to 100% (1/1) and 54% (13/24) in As patients. Wefound higher (p<0.05) seropositivity in older patients (n=8) among symptomatic and positives for viral RNA (n.23). CONCLUSIONS: It has been observed that a dual approach of serological and molecular tests detects a higher absolute number of disease cases in a pandemic context,whichcould improve monitoring and health surveillance efficacy. The age-related seropositivity frequency in this study, if confirmed, could enhance the validity of serological tests, especially in older patients.In these subjects, molecular positivity accompanied by serological positivity (distinct for M and G immunoglobulins) should help determine disease status and support decisions related to patient management.