The title was a little dry so I had to include this photo:
The CDC revised their guidelines for how long a person should isolate themselves after being diagnosed with Covid-19 or with assuming that they have it based on exposure and symptoms. Previously, it had been recommended that it be 7 days of quarantine after the onset of symptoms AND at least 3 days after recovery. Here is the summary. I have also included the link to the CDC’s webpage . On the CDC’s webpage they include the rationale for making that recommendation. We read a lot about how long the virus can be present on various surfaces or be present in nasal passages, but this is evidence of viral particles and doesn’t necessarily mean that this is an infectious virus.
Here is the term to impress your friends: replication-competent virus in viral culture (as a proxy of the presence of infectious virus)
Recommendation: For persons recovered from COVID-19 illness, CDC recommends that isolation be maintained for at least 10 days after illness onset and at least 3 days (72 hours) after recovery. Illness onset is defined as the date symptoms begin. Recovery is defined as resolution of fever without the use of fever-reducing medications with progressive improvement or resolution of other symptoms. Ideally, isolation should be maintained for this full period to the extent that it is practicable under rapidly changing circumstances.
While this strategy can apply to most recovered persons, either a test-based strategy (if feasible) or a symptom-based strategy with more stringent requirements may be used for recovered persons for whom there is low tolerance for post-recovery SARS-CoV-2 shedding and infectious risk because they are:
- Persons who could pose a risk of transmitting infection to
- Vulnerable individuals at high risk for morbidity or mortality from SARS-CoV-2 infection, or
- Persons who support critical infrastructure
- Persons normally residing in congregate living facilities (e.g., correctional/detention facilities, retirement communities, ships) where there might be increased risk of rapid spread and morbidity or mortality if spread were to occur.
- Persons who because they are immunocompromised may have prolonged viral shedding.
The correlation presented here between Ct values (Cycle threshold) and the ability to recover replication-competent virus is presently only applicable to upper respiratory specimens (mostly nasopharyngeal swabs) that have been assayed at CDC. These data are presented as one of a variety of pieces of evidence to inform this interim guidance. This relationship should not be inferred to apply to Ct values obtained by other laboratories or used to define a strict Ct cutoff. At this time, Ct values should not be used to define infectiousness or demonstrate the absence of risk for transmission.
Here is a description of Ct value:
CT value stands for Cycle Threshold value. At its simplest, the CT value represents the first cycle during testing in which a detection occurs. Low CT values indicate a test’s ability to detect positives early in the diagnostic process, or sooner than those of higher CT values. More technically, the threshold is the numerical value assigned for each run of a test. Each threshold value reflects a statistically significant point above an established baseline. The CT value represents the PCR cycle number, or point at which a diagnostic tool first detects a noticeable increase in fluorescence above a baseline signal. When testing identical samples with two separate real time PCR assays the one with the lower CT value would represent the most sensitive assay.