Question: In mid August, our 30 yo nanny is travelling first to Arizona (ack!) to visit her parents, and then to Cancun with friends for vacation. We want to do our best to make sure she’s COVID-free before returning to work. Starting the day she returns home, we are planning to have her quarantine for a week, to see if she develops any symptoms. I thought it might also be wise to have her get a COVID test, to see if perhaps she was indeed infected, but is asymptomatic. My questions are: 1. Is having her stay away for 7 days post-return reasonable, or should we wait 10 or even 14? 2.If she gets a test, how soon can she get it and it still be useful? For example, going off our 7 day quarantine timeframe, if she gets the test on day 4 of being home, and we expect to get results 3 days later (in time for her to hopefully return to work on the 8th day), is there utility in getting a test that early? Would it show COVID infection if indeed there was one?
Answer: Any travel internationally necessitates 14-day self isolation upon return, per CDC (Figure 1). This 14 day period stems from data that show COVID-19 symptoms generally begin 5 days after exposure (range 2–14 days) (further described in Q&A of 3/29 and more recently this paper from Annals of Internal Medicine, which found that 97.5% of people who develop symptoms will do so within 11.5 days). In answer to your first question, your nanny needs to stay away from you and others for the full 14 days.
When it comes to your second question on how soon COVID tests can detect the virus, this is still an area of scientific exploration (read: we don’t fully know). For the most common swab tests (e.g. PCR tests), we can be confident that a positive result is a true positive (for more on PCR tests, see Q&A of 3/9; for more on sensitivity/specificity, see Q&A of 4/15), but we can’t be so confident in a negative result. This overview from Harvard Medical School offers a synthesis of findings from this study on false negative rates published in mid- May by Annals of Internal Medicine:
“If you get the nasal/throat swab or saliva test, you will get a false negative test result:
- 100% of the time on the day you are exposed to the virus. (There are so few viral particles in your nose or saliva so soon after infection that the test cannot detect them.)
- About 40% of the time if you are tested four days after exposure to the virus.
- About 20% of the time if you develop symptoms and are tested three days after those symptoms started.”
And when it comes to how long a person must wait for results to be returned, this really depends on lab capacity and test type. Generally, test results are available in 2–5 days.
To sum up, if your nanny goes the full 14 days without symptoms, she doesn’t need to get tested. If she chooses to skip her planned international travel and your family cannot be without her for 2 weeks, one happy(ish) medium could be to do as you suggest — ask her to self-isolate after returning from Arizona, get tested on the 4th day, and return to work when she receives her negative test result, assuming she remains without symptoms (this would likely be 7–9 days after her return).
Figure 1. Returning from International Travel
