Stopping and Starting the COVID-19 Isolation Clock: Fever, Symptoms and Testing

After joining the estimated 517 million worldwide with COVID-19 and beginning Paxlovid therapy, the skeptical cardiologist was next confronted with how best to avoid transmitting to those around him the SARS-CoV-2 virus, which was feverishly trying to replicate in his nose and respiratory system .

In January, the CDC updated its COVID-19 isolation and quarantine recommendations shortening both quarantine (for asymptomatic) and isolation (for “mildly” symptomatic people like myself) periods to 5 days, focusing on the period when a person is most infectious, followed by continued masking for an additional 5 days.

When Does the 5-day isolation Clock Start?

If you have mild symptom (e.g., fever, cough, sore throat, malaise, headache, muscle pain, nausea, vomiting, diarrhea, loss of taste and smell, without shortness of breath, shortness of breath, or abnormal chest imaging) day 0 of isolation is the day of symptom onset, regardless of when you tested positive,

It is not a simple, straightforward process to determine the day of symptom onset. We are in peak spring pollen season in St Louis. Allergy sufferers can experience cough, malaise and headache as they react to tree pollens which are hard to differentiate from an infectious illness. After a long, busy, stressful day of seeing patients, it is not unusual to be fatigued (aka malaise.) I’ve tested myself many times for COVID due to nonspecific symptoms like these and had previously always been negative.

My symptoms (primarily fatigue) begin May 5th making this day 0 of the isolation timer.

The CDC advises persons with mild symptoms to isolate for a full 5 days after symptom onset (i.e., days 0 through 5) and until symptoms have improved.

If you continue to have fever or your other symptoms have not improved after 5 days of isolation, you should wait to end your isolation until you are fever-free for 24 hours without the use of fever-reducing medication and your other symptoms have improved. Wear a well-fitting mask for 10 days following your onset of symptoms to limit spread to others in the home or other close contacts.

If you are asymptomatic (never developed symptoms), day 0 is the day you were tested (not the day you received your positive test result) and you should isolate for “a full 5 days” after that positive test. “If you develop symptoms soon (i.e., within a week) after your positive test result, the clock restarts at day 0 on the day of symptom onset.”

When Does the Clock End?

After contracting COVID if you aren’t a “patient-facing” health care provider like the skeptical cardiologist you can use the CDC’s online quarantine and isolation calculator.

The CDC has an online quarantine and isolation calculator to help guide patients through this somewhat confusing algorithm. The calculator asks if you have symptoms, if and when you had a positive test and if and when you had fever.

This calculator is for “people who have been in close contact with someone with COVID-19 or have COVID-19 to determine if they need to isolate, quarantine, or take other steps to prevent spreading COVID-19.”

As my day 0 was May 5th, my day 5 was May 10th and I can per CDC guidelines stop my isolation tomorrow May 11th.

The Importance of Fever

The CDC calculator asks if you have had a fever and when it ended (without the use of fever reducing medication like Tylenol or NSAIDS like ibuprofen.

As I have written previously, current cut-offs for the definition of fever are too high because the average temperature of humans has dropped significantly since normal temperature ranges were first established. My normal temperature is 97 degrees Fahrenheit. When I hit 99.9 degrees I felt warm and was 2.9 degrees above average yet below the CDC point for fever:

CDC fever is defined as “subjective fever (feeling feverish) or a measured temperature of 100.0F (37.8C) or higher” and for me that resolved 5/9/22.

Work Restrictions for Health Care Workers

For health care workers a return to work is more complicated. Here’s a graphic from the CDC on recommendations.

As far as I can tell in discussing these work restrictions with HCPs in other medical systems, the work restrictions vary by community level of COVID-19 (currently low in St. Louis City and County), the supply of HCPs, and the (often proprietary) policies of individual health care systems.

In a “contingency” situation (which seemed to be the case during the last large Omicron surge) physicians could return to seeing patients in 5 days with or without a negative test as long as they their symptoms were improving.

CDC defines “contingency” as “”when staffing shortages are anticipated.”

I have spoken in detail with SLU Employee Health to determine my appropriate return to work. Of course I will wear my Kimberly-Clark N95 continuously while in the office and when facing patients and will insist that all patients I’m seeing are wearing properly fitting masks as well.

Test To Treat Strategy Works

My COVID-19 case so far is a good example of the test to treat (T3) strategy advocated by Michael Mina. “This requires a well-choreographed one-stop system: 1) rapid test diagnosis of COVID-19; 2) an evaluation and, if medically indicated, a prescription by an authorized medical provider; 3) rapid dispensing of the medicine through a local pharmacy, health-care provider, or direct delivery to the home.”

Michael Mina, MD, PhD is an immunologist and epidemiologist who tweets helpful, cutting edge COVID-19 information regularly.

Symptoms Start Earlier in the Vaccinated

I found his graphs showing how vaccinations cause patients to have symptoms earlier after infection very helpful in understanding how I could have had a negative rapid antigen test followed 15 hours later by a positive test. These tweets show this phenomena may also be contributing to some Paxlovid rebound cases.

I am rapidly improving and now on day 4 of the Paxlovid. No fever since taking my second dose. I’m definitely going to continue 5 day course given concerns about rebound. The metallic taste persists but no other side effects.

I have yet to address isolation from family members with COVID-19. Will the former eternal fiancee’ dodge her date with Omicron?

Eric Topol’s latest Substack article makes it seem unlikely:

we are now facing the rise of the BA.2.12.1 variant (37% of new cases as of April 30 by CDC) and have learned quite a bit about it in recent days. It has a substantial transmissibility advantage beyond BA.2, which was already 30% more transmissible than BA.1, and reduced cross-immunity to BA.1 such that the people who had Omicron BA.1 infections (estimated to be at least 40% of Americans) may be susceptible to reinfections by this variant

Skeptically Yours,


Clock image by Brigitte Werner from Pixabay


3 thoughts on “Stopping and Starting the COVID-19 Isolation Clock: Fever, Symptoms and Testing”

  1. Thank you for this. Can you address the frequency of symptom rebound after Paxlovid? A half-dozen vaccinated and boosted family members all took Paxlovid, and all experienced rebound with another 5 days of isolation needed. How does this change the calculus of who should take Paxlovid?

  2. Thanks for all the great information. My Internist wife works in several ICU loaded with six COVID patients. To date she has tested negative. I no longer work in direct patient care but my age of 74 puts me at risk. I am also Mr. Mom for our 8-year-old daughter giving me exposure to a broad range of people. To date I have been negative and we have had 3 vaccines and a booster. So far, so good.


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