Meditations On Probability

After almost six years since the start of the pandemic, I finally caught COVID. Since Pica and I are two of those rare people who still continue to take infection risks seriously (e.g.. we avoid indoor gatherings, and are scrupulous about masking in public indoor spaces), I have been pondering the nature of rare events. Or given enough repetitions of a low probability event, it is not surprising to see it occur eventually.

Here is the timeline. Pica spends three weeks back east with her family, During this period I am not venturing out much, except for walks and a weekly trip to the grocery store. Pica returns on Saturday 4 October. Because she passes through the infectious soup that is modern air travel, we follow an isolation protocol for five days: she sleeps in the spare room of our next-door neighbor, and doesn’t come inside our house without being masked. (The weather is nice, and we can eat outside happily).

On Tuesday 7 October one of our two cats Esme starts sneezing a good bit. I wonder if she picked up a leurgy from Pica’s luggage still sitting in the living room.

On Thursday 9 October I feel a touch like I’m catching a cold, and by the morning of Friday 10 October I am clearly crook with what feels like a mild cold. Pica meanwhile Thursday tests negative for COVID, and we exit our isolation protocol. I’m wondering if I picked up a cold from Esme, who was still sneezing a lot. Though on Saturday I read that cat-to-human cold transmission doesn’t in fact occur.

On Sunday it still feels like a mild cold but since I had a dental appointment on Monday I decide I had better test for COVID. Oops. The antigen test comes up positive, as does repeating with another test kit from a different manufacturer.

Based on the timing of things, it was likely I was infected sometime between Saturday October 4 and Monday October 6. The possibilities I come up with are all low probability events:
a) On Saturday I went to the co-op to pick up some groceries. But the co-op is well-ventilated, and I am masked with an N95.
b) On Sunday I pick up takeout burritos from Chipotle. But this is a two minute task, and I am wearing an N95.
c) I pass through somebody’s infectious plume on one of my walks. Perhaps this was when I was sketching the jazz band on Sunday.
d) Somehow Pica’s return introduced COVID to the house, although she’s been asymptomatic throughout. Fomites on the luggage?

As for Esme, cats do in fact get COVID, and there has been at least one documented transmission event of COVID from cats to humans. I don’t think that’s what happened here though. She is not sneezing now, and is leaping up the walls with high energy.

I am isolating now in the spare room, and feel quite fortunate that I got my annual COVID booster almost three weeks ago on 18 September.