The latest update from the CDC incorporates evidence that informs the duration of isolation and precautions recommended to prevent transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to others while limiting unnecessary prolonged isolation and unnecessary use of laboratory testing resources.

One of the key findings in the CDC update is that concentrations of SARS-CoV-2 RNA measured in the upper respiratory specimens decline after onset of symptoms. Further, the likelihood of recovering replication-competent virus also declines after onset of symptoms. For patients with mild to moderate coronavirus disease 2019 (COVID-19), replication-competent virus has not been recovered after 10 days following symptom onset.

A large contact tracing study demonstrated that high-risk household and hospital contacts did not develop infection if their exposure to a case patient started 6 days or more after the case patient’s illness onset, according to the CDC report. However, recovered patients can continue to have SARS-CoV-2 RNA detected in their upper respiratory specimens for up to 12 weeks, even if the replication-competent virus was not isolated 3 weeks after symptom onset.

An assessment of the current data concluded that a person with mild to moderate COVID-19 remains infectious no longer than 10 days after symptom onset. Additionally, those with more severe to critical illness or who are severely immunocompromised will likely remain infectious no longer than 20 days after symptom onset.

A person who has recovered can continue to shed detectable SARS-CoV-2 RNA in upper respiratory specimens for up to 3 months after illness onset, according to the report. Studies have not found evidence that clinically recovered persons with persistence of viral RNA have transmitted SARS-CoV-2 to others.

The CDC has updated its recommendations based on this information, warranting an extended duration of isolation and precautions for up to 20 days after symptom onset for those with severe illness. For those who never developed symptoms, isolation and other precautions can be discontinued 10 days after the date of their first positive RT-PCR test for SARS-CoV-2 RNA.

For anyone who is severely immunocompromised, a test-based strategy could be considered in consultation with infectious disease experts. For others, a test-based strategy is no longer recommended except to discontinue isolation or precautions earlier than would occur under the recommended strategy above.

According to the CDC, for anyone who was previously diagnosed with symptomatic COVID-19 who remained asymptomatic after recovery, retesting is not recommended within 3 months after the date of symptom onset for the initial COVID-19 infection. In addition, quarantine is not recommended in the event of close contact with an infected person.

Among individuals who develop new symptoms consistent with COVID-19 during the 3 months after the date of initial symptom onset, if an alternative etiology cannot be identified by a provider, then the person may warrant retesting. Further, isolation may be considered during this evaluation based on consultation with an infection control expert, especially in the event symptoms develop within 14 days after close contact with an infected person.

For individuals who have never developed symptoms, the date of the first positive RT-PCR test for SARS-CoV-2 RNA should be used in place of the date of symptom onset.

Serologic testing should not be used to establish the presence or absence of SARS-CoV-2 infection or reinfection, according to the CDC report.

Duration of isolation and precautions for adults with COVID-19. CDC. Published July 22, 2020. Accessed July 23, 2020.