Ever since publishing my previous entry on my putative Covid-19 infection, I have been asked on several occasions how I think I caught the bug. Keeping in mind, again, that I have not yet been tested (due to lack of broad availability of kits for low-priority people, a group of which I am proud and relieved to be a member), I thought I would try and isolate how this might have happened in case future tests return positive.

I am not attempting a comprehensive correlative or causative study here; it is a relatively superficial and qualitative thought experiment on where and when this could have happened to try and understand how easy/hard it is for the virus to spread.

Note: I have linked to several data sources in the previous article for facts that I have restated here.

Here are the data points so far:

  1. I first felt symptoms (dry throat) on March 14th. I define this as Day 1.
  2. The first day I felt the fever was Day 4.
  3. The fever lasted till about Day 9.5. I did not have a thermometer so it was difficult to say with certainty, but assuming the morning fever stopped after Day 8 and the evening weakness stopped at Day 11, I am averaging this to Day 9.5.
  4. Anosmia and ageusia started on Day 8. It has continued into Day 14 consistently. I felt some restoration of taste on Day 15, so I will assume, for the purposes of this article, that things will continue to get better going forward.
  5. The median incubation period for covid-19 seems to be just over 5 days, with most cases showing symptoms latest at 11.5 days. This puts my infection date somewhere between March 3rd and March 9th, assuming I am a normal case for incubation and not an outlier.

In order to break up the text in this article and provide visual relief, I have made a simple qualitative health score chart chronicling 15 days of illness. The score goes from 1-10 and I assigned it each day based on how I thought I felt. No hard science here!

Qualitative Health Score per Day of Illness

Graph created with https://www.onlinecharttool.com/

  1. Between March 3rd and March 9th, I:
    • Went to work as normal on weekdays (I did not go past March 10th). My work commute is entirely on public transport and takes around 2.5 hours each way, on average. I tried to minimise interaction with other commuters but there were several instances of rush hour travel on the Tube and trains, so I will assume the culprits here could be other passengers on the Tube, or the various surfaces (tables, poles, chairs) in the carriages. I used hand sanitiser often. I was also very careful to maintain social distance with my colleagues, and happily, none of them seem to have contracted it.
    • Played badminton on several occasions. We were careful to use the "elbow shake" or the fist bump during gestures of sportsmanship, and I was diligent about using hand sanitiser often.
    • Went to the gym. The gym was quiet when I trained, and I was careful to wipe down surfaces and use hand sanitiser. I maintained social distance from my trainer during my training sessions.
    • Went swimming on several occasions. The pool was always quiet, so there were no issues with personal space. The chlorine would only have helped with keeping clean and disinfected.
    • Went grocery shopping, again being careful about maintaining social distance.
  2. Whenever I came home from being outside, I washed my hands thoroughly.
  3. I was careful not to touch my face, but absent-mindedly could easily have done so.

Based on these observations, the obvious transmission vectors are the various surfaces on public transportation or silent transmission from work colleagues. Despite diligent use of hand sanitiser during the commute, and hand washing at work or at home, an inadvertent scratch of the nose or wiping of my eye could easily have triggered the process. It is less likely I caught it through recreational activities, but there is still a small chance.

Given my relatively tame schedule during this time period, my infection shows just how easily the virus could spread, even with proper precautions in place. Once I felt ill, I self-isolated for well past the recommended 7 days to be absolutely sure I was free of illness.

To be clear, the virus is a wimp. It is actually not special when compared to other, more serious viral illnesses (like ebola). It mutates relatively slowly, meaning targeted immunology and DNA/RNA sequencing approaches could lead to long-term vaccines (something we cannot yet achieve with 'flu or even the common cold). However, it has several important properties that lead to increased transmission and annoyance:

  • A relatively long incubation period compared to a cold or 'flu, meaning it can silently be passed on to others before symptoms manifest.
  • Asymptomatic infection for many people (especially children), meaning these people may not properly self-isolate and again, silently pass it on to others.
  • Increased affinity of its surface proteins to the ACE2 receptor in the lungs (meaning once it gets in, it is significantly more likely to stick around). This is why it is important to wash your hands.
  • Viability on different surfaces - I am not sure if it is particularly more or less viable than other virus particles, but the fact remains that it can survive on different objects and be picked up through touch
  • A relatively long period of symptoms (dry cough, fever et c.), requiring diligent self isolation for 7 days (and at least 14 days for family members in the same house as someone who is affected).

Staying indoors and social distancing are effective mechanisms to control the spread of any illness, although I am quite impressed by the success of several Asian countries in containing the spread of covid-19 without resorting to strict lockdown measures, as described in this article. It is clear that most other countries, companies, and organisations reacted sluggishly to the spread, so it would be interesting to see how they tune themselves and learn from the Asian nations described in the previous link to avoiding rapid virulence in the future. We did a decent job learning from SARS, for example; keep in mind that even though we might be dissatisfied with the responses in our respective countries, these responses are still markedly superior to what we might have done had we not learnt and adapted from the SARS experience!

I will update this article as I continue thinking about how I might have caught it, but hopefully this is a decent first pass for my readers. Of course, the smoking gun for this and the previous article will be the covid-19 test, which I intend to take as soon as it is broadly available.