Patients with coronavirus disease 2019 (COVID-19) infection may respiratory tract
specimens positive for severe acute respiratory coronavirus virus 2 (SARS-CoV-2) for
several days while in isolation precautions or for several weeks after removal from
isolation precautions. This situation creates a dilemma for infection control staff
in acute and chronic healthcare settings and for public health officials. Potentially
keeping such patients in isolation precautions beyond the period when they are no
longer infectious leads to unnecessary actions and consequences: personal protective
equipment use; single-patient room occupancy; repeat PCR testing; social isolation;
delay from reentering the work force, particularly problematic for healthcare workers
and essential civil servants; and redistribution of infection control and public health
human capital assigned to track the status of such individuals. These downstream effects
have unequivocal and profound economic impact that may be avoidable.
Can patients in isolation precautions with COVID-19 infection be removed from precautions
prior to current guidelines?
Yes isolation precautions can be removed after 9 days from symptom onset or after
9 days from the first positive SARS-CoV-2 PCR test of a respiratory specimen in asymptomatic
individuals.
No reports, known to this author, of viable SARS-CoV-2 detection in respiratory tract
specimens collected beyond 9 days after symptom onset have been published.
1-3
As with other emerging viral infections,
4
patients with a high SARS-CoV-2 PCR cycle threshold (eg, cycle threshold ≥34 in one
study
5
or >24 in another
3
) have not been found to have live virus in their respiratory secretions. Similar
findings at CDC have been found with a cycle threshold >33 with the N1 amplification
target.
6
A study in Taiwan
7
included 100 patients with COVID-19 infection and their 2,761 close contacts (face-to-face
contact for >15 minutes with a confirmed COVID-19 patient). SARS-CoV-2 PCR testing
was performed on all symptomatic contacts (ie, contacts with fever, cough, or other
respiratory symptoms). SARS-CoV-2 polymerase chain reaction (PCR) testing was also
performed on all household and hospital contacts, regardless of symptoms, when they
were initially assessed. If PCR testing was negative, they were tested again if they
developed such symptoms during the 14 days after their initial contact with a case
patient. The investigators found no secondary COVID-19 infections among 852 contacts
exposed to infected cases if the exposure occurred after the initial 5 days of symptom
onset. These epidemiologic data support the aforementioned laboratory data.
Are there exceptions?
Yes, severely immunocompromised patients may be an exception. Based on data from other
viral infections,
8,9
patients with COVID-19 infection who are severely immunocompromised may have prolonged
shedding of live virus. Thus, decisions regarding discontinuing isolation precautions
for severely immunocompromised patients, or possibly those who are otherwise critically
ill with COVID-19 infection, should be based on a high SARS-CoV-2 PCR cycle threshold.
3,5,6
Importantly, the cycle threshold varies depending on the PCR protocol and amplification
target used in the PCR assay. Such patients, and all others, should continue to follow
CDC and local health official guidance regarding continued source control after hospital
discharge (ie, mask use and hand hygiene), as well as social distancing.
Are patients infectious if they previously had a COVID-19 infection, met criteria
for removal from isolation precautions, and they have SARS-CoV-2 PCR-positive respiratory
tract specimens over the next several weeks?
In most cases, no. The Korean CDC studied 285 SARS-CoV-2 PCR-positive patients after
removal from isolation precautions and an average of 45 days after symptom onset (range,
8–82 days); 126 still had some COVID-19 related symptoms.
10
All 285 were seropositive. SARS-CoV-2 culture was negative in 108 patients who had
such cultures performed. These 285 patients had 790 contacts, including 351 family
members. Contacts were monitored for minimum of 14 days each. SARS-CoV-2 PCR testing
of contacts was performed if they became symptomatic (ie, either temperature ≥37.5°C,
sore throat, cough, etc); otherwise, PCR testing was done on day 13 after the exposure
if the contact was a healthcare worker or household member (YJ Choe, personal communication).
There was no evidence of COVID-19 transmission to these contacts: 27 of the 790 contacts
were previously SARS-CoV-2 PCR-positive, and 3 newly SARS-CoV-2 PCR-positive contacts
had other high-risk exposures.
Are there exceptions?
Yes, severely immunocompromised patients or reinfection in those patients or others
may be exceptions. For severely immunocompromised patients or if otherwise in question,
the SARS-CoV-2 cycle threshold will assist in determining infectivity. Reinfection
with SARS-CoV-2 remains an open question. At this time, it is unclear when to assess
patients for possible reinfection and the risk of disease transmission if that occurs.
After COVID-19 infection, SARS-CoV-2 IgG antibodies remain significantly elevated
for at least 7 weeks in most cases
11
; however, 6% of patients with relatively mild COVID-19 infection have been found
to recover without detectable neutralizing antibodies.
12
Neutralizing antibodies can be detected for 2 years in ~90% SARS-infected patients.
13
However, antibody levels drop after 2–3 years in patients who recovered from SARS
and MERS-CoV infections.
14
Reinfection from the same genotype of human coronaviruses can occur within months
to a year later.
15,16
Since SARS-CoV-2 neutralizing antibodies are protective in rhesus macaques,
17,18
and if durability of these antibodies is similar to that of patients who recovered
from SARS and MERS-CoV infections, SARS-CoV-2 PCR positivity beyond 9 days from symptom
onset is unlikely to reflect reinfection over the ensuing months in seropositive immunocompetent
patients. However, if neutralizing antibody levels wane after several months to a
year, then SARS-CoV-2 PCR positivity may reflect reinfection, and the SARS-CoV-2 cycle
threshold will assist in determining the need for isolation precautions or quarantine.
Based on the aforementioned data, patients with COVID-19 infection who are beyond
9 days from symptom onset or beyond 9 days from the first SARS-CoV-2 PCR-positive
testing of a respiratory specimen in asymptomatic patients, should not undergo repeat
SARS-CoV-2 PCR testing unless they are presenting several months after symptom onset
or asymptomatic detection (ie, long enough time for possible reinfection), or they
are otherwise severely immunocompromised. The patient should not be placed back in
isolation precautions unless severely immunocompromised. Immunocompetent patients
with a SARS-CoV-2 PCR-positive respiratory specimen obtained >9 days after symptom
onset, or first positive testing for asymptomatic patients, should be allowed to have
procedures, surgical or otherwise, or to undergo testing as clinically indicated without
the precautions used for patients with active COVID-19 infection unless they are presenting
several months after either symptom onset or their initial positive SARS-CoV-2 PCR
testing, or they are severely immunocompromised. In such cases, determination of SARS-CoV-2
cycle threshold will assist in decisions regarding infection control precautions.