My long-distance partner has COVID; her symptoms first started ~10 days ago. She is now symptomless (except fatigue), but is still testing strongly positive on rapids. If she comes to visit me, what are the odds she's still contagious? More generally, how much weight do you place on "symptomless and 10+ days from onset" versus "testing positive on rapids" in modeling contagiousness?

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I'm sorry that this is all I have to contribute, I don't know anything about the duration of contagiousness but I still have some potentially decision-relevant factors.

The rapid antigen tests have a history of really high false negativity rates: but this doesn't mean they are sensitive in a trustworthy way, it's more of an indicator that the people making them aren't trustworthy people.

You want to use p100 masks, not n95 masks (they are available at large hardware stores and Amazon). My model since last winter is that the current strain infects most people who aren't wearing p100 masks when they go to shared indoor spaces, although the herd immunity since then might mean that it's infecting closer to 10-50% of the country (US) instead of 95-99%.

My understanding is that rapid antigen test positives indicate high viral load, especially if the line is darker rather than lighter. So I would expect her to still be significantly contagious.

Being symptomless does help prevent transmission some, since she won't be coughing or blowing her nose. But regular talking, and to a lesser extent breathing, are often enough to transmit it.

You didn't ask this, but if I were you and I wanted her to be able to still visit while minimizing risks, I would consider some or all of the following:

  • Having her sleep alone unmasked in a room with a HEPA filter (and a window cracked if your weather is mild)

  • Spending much of your days outdoors with at least surgical quality masks on

  • Wearing at least N95 quality masks, preferably silicone-sealed N95s (Softseal 3D masks), while indoors together

  • Using improved ventilation such as HEPA filters, continuous HVAC, and/or open windows if the weather allows, while indoors together.

You could also consider not minimizing risks as much as you theoretically could, especially if you've had Covid or a bivalent vaccine within the past four months, don't have any high risk conditions, have access to Paxlovid, don't have any other upcoming events you'd hate to miss, and are willing to take extra precautions around vulnerable people for the week or so after she leaves.