from Hacker News

How many microbes does it take to make you sick?

by meany on 10/1/23, 4:03 PM with 109 comments

• by gregwebs on 10/1/23, 6:27 PM

  Great to see statistical thinking. There have been a lot of Covid shouting matches because people are trying to reduce things to binary. Masks don’t work! Actually, they work as advertised- only 95% effective at best (and a cloth mask may be 30%), not a binary protected or not. That’s effective at blocking particles. You are still guaranteed to get some virus particles. They are going to be in your respiratory tract trying to replicate, and maybe some are replicating-does that mean you are infected in a clinically meaningful way? Depends.

  Researchers will try to measure if some intervention like that works reporting binary PCR positive or negative- but we should want to know what was the severity of the illness. PCR positive with minor illness can be a good outcome indicating that the intervention helped lower the innoculum.

• by curiousObject on 10/1/23, 4:22 PM

  >A tiny enough dose may even serve to remind our immune system of a pathogen’s existence, boosting our antibody response to keep us protected against it.

  This article should be required reading, whatever your views on Covid and other conditions.

  Although the attack method of the infection is significant, and the potential victim’s defenses are significant, the raw quantity of infectious agent and the exposure rate are also both important

  Nothing is certain. Everything is statistics.

• by sulam on 10/1/23, 5:42 PM

  Just keep in mind, dose-dependence is variable. It’s not a virus, but even one cryptosporidium oocyst is enough to get you sick.

• by zby on 10/1/23, 7:51 PM

  If 400 microbes that contact your body makes you sick - then what if one virus gets into a cell and produces 400 copies? It is certainly possible: "For example, SIV, a cousin and model for the HIV virus, is released from infected T cells with a burst size of ≈50,000 (BNID 102377) whereas cyanobacterial viruses have characteristic burst sizes of ≈40-80" http://book.bionumbers.org/how-many-virions-result-from-a-si... So if not just one - then a few initial virions should be able to produce the infectious dose.

  I guess time is important here - the organism detects the initial virions and prepares defences - so if the infectious dose amount of virions comes after the organism is warned they fail to grow into an infection. But my intuition is that the complexity of that process and path dependence makes that infectious dose so variable - that it does not seem to be any useful.

• by 3seashells on 10/2/23, 5:16 PM

  A fascinating thing is that you can catch a infection early. If you know you have been exposed and time it right you can induce a artificial fever via sauna or steam bath. This catches the whole infection ahead of the curve and shortens reconvalescing and downtime significantly.

• by swayvil on 10/1/23, 4:51 PM

  There is also bodily vigor to consider.

  When you are strong you are resistant. When you are weak you are susceptible. The difference can be huge.

  It's a good argument for clean living, regular exercise etc.

• by thenerdhead on 10/1/23, 5:46 PM

  > Exposure is a function of pathogen concentration and contact time, so if you can reduce either of those, you can better avoid infectious diseases.

  What these articles don't talk about are the real-life challenges of concentration and contact time. For example, being a parent with a kid in school they might randomly sneeze or cough in my face while being completely asymptomatic. Then of course we all come down with covid later on.

  Secondly, the claims about viral load and shedding have conflicting science on new variants too:

  > https://www.nature.com/articles/s41591-022-01816-0#Sec7

  i.e

  > Nevertheless, in our study, correlation between RNA and infectious VL was equally low between fully vaccinated and unvaccinated Delta-infected patients, indicating that factors other than mucosal neutralizing antibodies may be important for the reduction in infectious VL

  > Within 5 DPOS, we found higher RNA VLs but lower infectious VLs in swabs of unvaccinated patients with pre-VOC infections compared to Delta. These results disagree with other studies that analyzed only nucleic acid detection and found 3–10-fold-higher RNA copy number in Delta-infected patients compared to pre-VOC-infected patients

  > Although VL is a key element of transmission, the process of human-to-human transmission is complex, and other factors, such as varying recommended protection measures, overall incidence, perceived risks and the context of contacts (household versus community transmission), can influence outcomes in the studies reported.

  The best point from this article is the following:

  > Transmission dynamics are complex, but the interventions we can take to protect ourselves are comparatively simple.

• by HocusLocus on 10/1/23, 9:59 PM

  Just one if it's a big one

• by PaulKeeble on 10/1/23, 6:36 PM

  Last paragraphs are really important recommendations for how to end the pandemic.

  "Masking, increased ventilation and distancing reduces the number of microbes you’re exposed to. Vaccination increases the infectious dose. "

  We really need to move beyond vaccine only, its not working Covid is just too transmissible.