Abstract
Background. In SARS-CoV-2 infection, viral RNA may persist in respiratory samples for several weeks after the resolution of symptoms. Criteria to assess the end of infectivity are not unequivocally defined. In some countries, time from diagnosis is the unique criterion used, in addition to symptom cessation. This study evaluates the role of the Lumipulse® Antigen Assay (LAA) for the safe end of isolation of patients ≥21 days after the diagnosis of infection. Methods. A total of 671 nasopharyngeal swabs from patients diagnosed with infection at least 21 days before were assessed by RT-PCR and LAA, and the role of LAA in predicting the absence of infectivity was evaluated by virus cell culture. Results. Viable virus was present in 10/138 cultured samples. Eight out of ten infective patients suffered from a concomitant disease, predisposing them to long-term shedding of infective virus. In particular, infectious virus was isolated from 10/20 RT-PCR+/LAA+ cultured samples, whereas no viable virus was found in all 118 RT-PCR+/LAA– cultured swabs. LLA and RT-PCR agreed in 484/671 (72.1%) samples, with 100% and 26.7% concordance in RT-PCR negative and positive samples, respectively. Conclusions. Viable virus can be found ≥21 days after diagnosis in immunocompromised or severely ill patients. LAA better than RT-PCR predicts non-infectivity of patients and can be safely used to end isolation in cases with long persistence of viral RNA in the respiratory tract.
Highlights
In SARS-CoV-2 infection, viral RNA may persist in respiratory samples for several weeks after the resolution of symptoms [1,2,3,4], but this does not necessarily indicate shedding of infective virions
All samples negative on RT-PCR were negative on the antigen test, with 100% concordance (Table 1)
Eight of 10 positive and 1 of 10 negative cultured samples were from hospitalized patients
Summary
In SARS-CoV-2 infection, viral RNA may persist in respiratory samples for several weeks after the resolution of symptoms [1,2,3,4], but this does not necessarily indicate shedding of infective virions. According to European Centre for Disease Prevention and Control guidelines, asymptomatic people should self-isolate for 10 days from the date of the sample collection, and severely ill patients should be isolated for at least and up to 20 days from the onset of symptoms, based on an individual case risk assessment [16]. Two consecutive negative SARS-CoV-2 RT-PCR tests, ideally in a 24-h period, are recommended for the discontinuation of isolation for immunocompromised or severely ill patients, especially in case of transfer to other hospital wards or discharge to a long-term care facility [16]. For patients infected by a non-beta variant, a negative molecular or antigenic test is required to discontinue isolation 10 days after symptom onset, and a symptomatic approach is used after 21 days. Infectious virus was isolated from 10/20 RT-PCR+/LAA+
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