Most patients with mild COVID-19 infection continue to shed SARS-CoV-2 from their upper airways for approximately 7-12 days. The duration of shedding is longer in severe cases, though in both mild and severe cases, significant variation is seen.
Viral shedding does not necessarily equate to infectiousness however. Viral shedding may decline to a level below the infectious threshold before it ceases completely, and/or non-viable virus may be shed.
In a small cohort of mild COVID-19 cases from Germany (n=9), viral loads and viral cultures were performed on a variety of specimens simultaneously. The virus was readily culturable from specimens taken during the first week of symptoms, but no positive cultures were obtained from samples taken after day 8. Importantly, this was despite ongoing high viral loads being detected at the time. The authors estimated that there would be a <5% chance of successful culture by day 10.
This work aligns with epidemiological modelling which suggests that infectiousness likely peaks near to the onset of symptoms, and falls rapidly over the course of a week thereafter.
For the above reasons, we recommend de-isolating patients with mild disease 14 days after symptom onset.
Patients with severe disease (i.e. requiring admission due to clinical instability) may continue to shed virus at higher levels for longer periods. We therefore recommend de-isolating such patients 14 days after clinical stability has been achieved (e.g. after supplemental oxygen was discontinued).
Patients who remain asymptomatic after a positive COVID-19 result can be de-isolated 14 days after their positive test. Although asymptomatic patients might be expected to be less infectious than symptomatic patients, the two groups’ viral loads appear to be similar, and we believe a similarly cautious approach to de-isolation is warranted.
Patients admitted to hospital can continue their isolation period at home once clinical stability has been achieved, provided that the criteria in table 2 are met.
It is common for patients to continue to have symptoms for longer than the above time periods. Full recovery may take several weeks. Patients who are still symptomatic at the end of their isolation period can be de-isolated provided that their fever has resolved (without the use of antipyretics) and their symptoms have improved.
It is not necessary to repeat PCR testing in order to de-isolate a patient.
Patients can remain PCR positive even after they are no longer infectious.
A positive PCR test does not equate to an infectious, viable virus.
Criteria for discharging patients from isolation (i.e., discontinuing transmission-based precautions) without requiring retesting:
• For symptomatic patients: 10 days after symptom onset, plus at least 3 additional days without symptoms (including without fever and without respiratory symptoms)
• For asymptomatic cases: 10 days after positive test for SARS-CoV-2
For example, if a patient had symptoms for two days, then the patient could be released from isolation after 10 days + 3 = 13 days from date of symptom onset; for a patient with symptoms for 14 days, the patient can be discharged (14 days + 3 days =) 17 days after date of symptom onset; for a patient with symptoms for 30 days, the patient can be discharged (30+3=) 33 days after symptom onset). *
Answers extracted from: Clinical management of suspected or confirmed COVID-19 disease (Version 4, May 2020)