SARS-CoV-2 RNA Persistence in Naso-Pharyngeal Swabs

Abstract

Since February 2020, Italy has been seriously affected by the SARS-CoV-2 pandemic. To support the National Health Care system, naso-pharyngeal/oropharyngeal swabs collected from suspected cases of Teramo province, Abruzzo region, are tested at Istituto Zooprofilattico Sperimentale dell'Abruzzo e del Molise G. Caporale, for the presence of SARS-CoV-2 RNA. Out of 12,446 tested individuals, 605 returned positive results at least once, with prevalence significantly higher in men. A reduction of the level of viral RNA in the first swab per each positive patient collected over time was also observed. Moreover, 81 patients had at least one positive sample and two final negative tests: positivity in swabs lasted from 14 to 63 days, with a median value of 30 days. This shows the potential for the virus to coexist with patients for a long time, although we highlighted intermittent positivity in several cases. The evolution of the SARS-CoV-2 epidemiological situation and knowledge on viral shedding should be closely monitored, to interpret the findings correctly and adjust accordingly the surveillance activities.

Keywords: Abruzzo; COVID-19; SARS-CoV-2; coronavirus; naso-pharyngeal swab; qPCR; viral shedding.

Figure 1

Temporal distribution of samples tested by results, and percentage of positive samples.

Figure 2

Mean values of CT N gene of the first positive swab per patient by month. * Asterisks are denoting the significant mean value of CT N gene (p-value = 0.0002).

Figure 3

Trend of C_T N gene mean values of the first positive swab per patient by week of sampling.

Figure 4

Number of patients distributed according to the range duration of qPCR positivity (Min = 14; Max = 63).

Figure 5

Scatterplot of C_T N gene values at the first positive swab and the SARS-CoV-2 RNA persistence in naso-pharyngeal/oropharyngeal swabs per patient.

Figure 6

Time variation of the CT N gene mean values of patients with final double negative swab. * Asterisks are denoting the significant mean values of CT N gene (p-value = 0.0001).