How many microbes does it take to make you sick?
145 points by meany 1 year ago | 109 comments- gregwebs 1 year agoGreat 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.
- macawfish 1 year agoI don't know if I'd call this "statistical thinking", at least not in the conventional sense of linear statistics with simple parametric models. If anything I'd call this "systems thinking", which unfortunately is not the kind of thinking I typically associate with "statistical thinking".
- PaulKeeble 1 year agoActually N95 is AT LEAST 95% effective. 95% is its worst case performance on a PM2.5 sized particle, at all other particle sizes it is better than 95% usually considerably. We also have N99 masks and even P100 respirators which do an even better job. We just need to start using them. We also need to educate ourselves how to fit and fit test a mask because if its leaking its not giving you that level of protection.
- hamburglar 1 year agoWell, the actual mask's performance is 95% effective, but you can't really make a guarantee about the overall worst case effectiveness when deployed by humans. N95 masks are not 95% effective on someone who has a big fluffy beard preventing a proper seal, for example. Or with people who use their gut feeling to decide where and when to put them on (like deciding if there's nobody in the elevator, you don't need it, ignoring the fact that someone may have gotten out of the elevator 20 seconds ago and left particulates in the air).
- avereveard 1 year agoI think that's about the material itself, then at the mask face interface you get all kinds of sealing issues
- weaksauce 1 year agoyou're absolutely correct and furthermore smaller particles and larger particles are easier for the masks to catch to state it differently if it wasn't clear.
- hamburglar 1 year ago
- ryanjshaw 1 year agoIf you want to be truly scientific you also need to discuss the risks of mask wearing. Then, in relation to COVID response, you have to weigh up the costs vs. benefits of a mask wearing policy.
Some of those costs are hard to quantify scientifically or intangible e.g. restrictions on individual freedom, and even the scientifically quantifiable data may have large variability so you have to take an opionated position. Different cultures will obviously take different positions due to different weights they place on risks and values.
Therefore, at this point you leave the realm of science and enter the realm of politics. For whatever reason, people like to pretend it's entirely a scientific discussion but it's not.
- lesuorac 1 year ago> Therefore, at this point you leave the realm of science and enter the realm of politics. For whatever reason, people like to pretend it's entirely a scientific discussion but it's not.
I mean discussions are typically both science and politics. Masks lower the amount of people that get sick is scientific fact; why do you think they wear them in the operating room? Whether or not that is "worth" wearing a mask is politics though. However, if you want to convince people of something (aka politics) you may want to appeal to them using logic and for that you'll want to use facts.
Having large variability doesn't make something not a fact. Plenty of males 20-24 do not get in car accidents but that doesn't mean that none of them will or that if you were to insure say 100k males 20-24 and 100k females 20-24 that the males wouldn't in aggregate have higher claims. But given a specific male and specific female its entirely possible that the female gets into an accident first.
- avidiax 1 year ago> if you want to convince people of something (aka politics) you may want to appeal to them using logic and for that you'll want to use facts
I used to think this way, but this advice needs to be conditional.
Dispassionate or distant parties can sometimes use facts to drive a decision. It's not even clear that it's the "correct" decision, since nobody has all the facts, and presentation, ordering, accessibility all matter tremendously.
Once you add an emotional reaction, well, people will logically or rationally pick or ignore facts to justify the emotion. Surely you've had someone tell you that you logically shouldn't be angry, and you greatly appreciated that insight and recalculated your emotions, right?
https://news.harvard.edu/gazette/story/2022/01/logic-or-emot...
- AvocadoPanic 1 year agoThey're worn in theater to prevent the surgical team from contaminating the sterile field they're all huddled together around.
- avidiax 1 year ago
- lesuorac 1 year ago
- macawfish 1 year ago
- curiousObject 1 year ago>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.
- Sakos 1 year agoThis is one of the reasons why masks are so important and why they don't need to be 100% effective. Just reducing the amount of viral load could turn a serious infection into something you might barely notice.
edit: Imagine this being controversial. I didn't realize there were Covid deniers and skeptics here, because what I've stated is completely within established science.
- sfblah 1 year agoWhat you said isn’t controversial. It’s definitely right.
The issue with masks is one side started treating them like a talisman that makes infection impossible, which provoked the other side to say they do nothing.
On a population level, masks are probably close to ineffective against a viral pathogen. You can read the relevant Cochrane review to see that.
On an individual level they obviously do something, but you have to consider other factors as well, such as level/frequency of exposure and the like. Studies from prior to the pandemic suggested that a perfectly fitted N95 mask dramatically reduced flu virus penetration. For a more normally worn N95 the reduction was about 70%. For a surgical mask it was essentially nil. Importantly, a perfectly fitted mask required essentially gluing it to the face of a mannequin.
Final point is, with an intervention whose impact is measurable but imperfect, you have to consider the side effects. I personally know several friends of my teenage kids who now have odd (to me at least) social phobias for which the only “cure” is to wear masks everywhere. Just last weekend I was talking to a friend of my daughter who wears masks everywhere except indoors.
- maxerickson 1 year agowhich provoked the other side to say they do nothing.
This somewhat excuses their reactionary stupidity. Like they weren't "provoked", the use of masks wasn't directed at them.
- kadoban 1 year ago> The issue with masks is one side started treating them like a talisman that makes infection impossible, which provoked the other side to say they do nothing.
This is an oddly biased framing.
- AnthonBerg 1 year agoThe un-cited Cochrane review in question does not say that.
From Cochrane.org:
Statement on 'Physical interventions to interrupt or reduce ... - Cochrane
Mar 10, 2023
Many commentators have claimed that a recently-updated Cochrane Review shows that 'masks don't work', which is an inaccurate and misleading interpretation. It would be accurate to say that the review examined whether interventions to promote mask wearing help to slow the spread of respiratory viruses, and that the results were inconclusive.
Repeating the important part:
the review examined whether interventions to promote mask wearing help to slow the spread of respiratory viruses
Conversely, here’s a good study that shows that consistent use of FFP3 respirator masks drastically reduced transmission among workers on a hospital ward: https://elifesciences.org/articles/71131
Note that the study only had the workers wearing FFP3 masks on shifts, and community transmission was high at the time. Therefore the study “leaked” and good masks work better than the numbers in the study might seem to indicate. Face-fitting masks do work, and very well. Of course they do. It’s all very clear if you dig into the aerosol physics.
- rootusrootus 1 year ago> For a surgical mask it was essentially nil.
Is the surgeon wearing a mask to protect himself from me, or to protect me from him?
- msie 1 year agoThat Cochrane review is faulty and one of the co-authors (Tom Jefferson) "works for the Brownstone Institute, a Covid-19 misinformation group that is powered by dark money."
https://www.theguardian.com/commentisfree/2023/feb/27/dont-b...
- maxerickson 1 year ago
- pton_xd 1 year ago> This is one of the reasons why masks are so important and why they don't need to be 100% effective. Just reducing the amount of viral load could turn a serious infection into something you might barely notice.
It would be nice to have some numbers to back this up. Let's suppose the "viral load" to acquire a Covid infection is 18 particles, the same as norovirus detailed in the article. And let's say you're exposed to hundreds of thousands of viral particles every minute you spend near a sick person [1]. If a mask reduces your viral load by 50%, is that a worthwhile method of avoiding infection?
- sfblah 1 year agoThere are good studies on viral load reduction from masking with flu viruses from before 2020. After 2020 the topic became politicized so the studies are probably unreliable.
- epivosism 1 year agoAll the factors you mention are scalar. You can wear 0,1,2,3 masks. You can be 1,2,3,10,20 feet away from the person for 0,1,5,10 minutes. I can come up with any number of such factors involving wind, lifetime of virus, the person's shedding rate, etc.
Given that, there will always be a border at which having an additional 50% coverage is useful. Where the actual line is, we don't know. But as long as protection is monotonic in the factors above, it's always valuable to have more protection, which implies even <100% effective masks are useful.
Trivial proof: Imagine someone with literally 10k masks all around them. You have to admit this is more safe than 1 mask. QED. You can call in meta factors like "in reality nothing matters" but you're arguing by consequences then, not actually disagreeing with the facts, just claiming they don't matter.
- MrLeap 1 year agoThe assertion is that if you dump a gooey grey gallon of pure covid on someone, their symptoms will be more severe than if they only get 18 virions. Do you suppose that wouldn't be the case?
- Jabbles 1 year agoFrom that link:
Our simulation also shows that wearing a mask can effectively reduce the spread of the viruses.
- sfblah 1 year ago
- meowkit 1 year agoEstablished science is an oxymoron.
Science is an on going process, always open to being overturned.
To the point of masks - I agree with your statement here, but a regular mask (filtered masks should help to some extent) will not protect you from an infected person. An infected person with a mask will reduce the chance of spreading their viral load.
This detail is where I feel people are talking past eachother. Most of covid denial to me seems to be about a psychological reactance to being told to mask up when they are not sick.
One might argue that the extra chance of reduced vectorization is worth mask mandates, but that simplistic purely “scientific” approach is its own problem. You have to argue people where they are at and convince them, not force the “right” view on them and then get upset they are “in denial” or skeptical.
- verve_rat 1 year agoYeah, there is a weird grouping of rabid anti-maskers here. Seems odd given the nominal audience of this site.
I just don't get the rejection of basic facts.
- JeremyNT 1 year agoThe audience of the site is very entrepreneurial and as such is libertarian leaning by and large.
Which is to say you shouldn't be terribly surprised that there is a general strain of "don't tread on me" in the discourse. Simply being told what to do is enough to elicit a strong negative response.
- JeremyNT 1 year ago
- User23 1 year agoRCTs show surgical and cloth masks to be ineffective or nearly so for reducing the spread of respiratory viruses. Obviously the kinds of masks used in BSL labs do work to prevent spread.
However there are statistics that areas with more masking had less severe illness. However that’s uncontrolled and some other factors or factors might account for both increased masking and reduced spread. That’s probably the case otherwise the RCTs would show efficacy.
All of the subsequent work is just computer models and doesn’t actually tell us anything empirical. Obviously it’s easier to create a model that produces the desired result than it is an RCT.
- mozman 1 year agoThere shouldn’t be any requirements for masks. Want to wear one? Great. Should I have to? No.
- amanaplanacanal 1 year agoIs fairly common that, if you as an individual are doing something that poses a risk to other people, society will step in to attempt to change your behavior. You can argue that it is “wrong” for society to do that, of course.
- the_gastropod 1 year agoIt puzzles me that nearly 4 years after the start of the pandemic, this naive libertarian thought fragment is still so widely used. As the saying goes, “Your right to swing your arms ends just where the other man’s nose begins”.
- maxerickson 1 year agoSo people shouldn't have freedom of association or control over their own property?
Or do you just mean universal requirements imposed by society at large when you say 'any'?
- amanaplanacanal 1 year ago
- elsonrodriguez 1 year agoThe exploration of truth is anathema to those who claim to already have the truth.
- refurb 1 year agoNo not really.
Infection is binary or not. You either get exposed to enough to actually result in replication inside your body or you don't. If you get exposed to a small amount and your immune system immediately eliminates it, that's not an infection.
The amount of exposure needed to actually cause an infection is different from person to person depending on their immediate immune response.
But it's not like reducing exposure by 50% reduces disease severity by 50%. Biology doesn't work that way.
- 1 year ago
- explaininjs 1 year agoThe simple fact of the matter is that having covid every now and then^ is far superior to wearing a mask always.
^ and the more you have it the less severe it is, until it asymptotically reaches a complete non-issue. As with the common cold.
- explaininjs 1 year agoThe downvoters might explain their distaste. But I cant expect them to do more than echo what the government told them.
- explaininjs 1 year ago
- sfblah 1 year ago
- dorfsmay 1 year ago> boosting ourantibody response
What I wonder is if we can develop immunity (not boosting, assuming never been infected before) from being exposed to small doses, or do we need at least one full blown infection.
- jameshart 1 year agoNot sure why you are suggesting the basic mechanism of inoculation, which has been known for centuries and is the fundamental mechanism behind vaccination, as if it’s a novel hypothesis. Have I misunderstood what you’re getting at?
- beebeepka 1 year agoI think your understanding is fine. A friend of my wife once came up with the novel idea of renting books out of big buildins that are loaded with books. Brain farts happen to all of us
- dorfsmay 1 year agoDosage. Vaccines use deactivated viruses, but I don't think they use "tiny amount".
- beebeepka 1 year ago
- refurb 1 year agoGenerally the stronger the immune response, the more effective the future immunity (not always).
- vikramkr 1 year agoYep that's called vaccination! No need to get a full blown infection it's how we eradicated smallpox
- dorfsmay 1 year agoVaccination is using deactivated viruses. My question is can we get the same effect from exposure to small doses of live viruses.
The articles says exposure to tiny amount can "boost" immunity, which I assume means an immunity acquired earlier from a full blown infection (or vaccination).
- yieldcrv 1 year agoI’ve gotten lots of anti vaxxers to be into vaccines by saying what the parent said, most of them are just allergic to the word vaccine and don’t know what it means, (specifically I’m referring to using dead pathogens not just a low dosage of live ones)
so just describe the procedure, and call it a secret that big pharma doesnt want them to know, and theyre into it. be anybody but a doctor lol
slam dunk
- dilyevsky 1 year agoThat’s not vaccination that’s inoculation which is how they originally prevented smallpox before they developed an actual vaccine
- refurb 1 year agoThat's not vaccination.
You get a hefty dose of vaccine. The difference is that it's either not an infectious agent at all (just a fragment of one) or it's a low-infectious agent.
- dorfsmay 1 year ago
- jameshart 1 year ago
- rand0mx1 1 year agoIt should be exposure time or do you mean something else with "exposure rate"
- wtallis 1 year ago"Exposure time" usually implies you're spending some period of time in proximity to an effectively unlimited reservoir of the pathogen (eg. an infected person coughing frequently) and your exposure is at some level of concentration that depends on the type/route of exposure, so that the total amount of pathogen that ends up in your body to challenge your immune system is proportional to the duration of time you spend being continually exposed.
A phrase like "the raw quantity of infectious agent and the exposure rate" is calling attention to the fact that one brief intense exposure vs repeated small exposures over a long time span may have vastly different outcomes despite presenting your immune system with the same number of microbes to deal with.
- slim 1 year agoit could mean how many times you have been exposed to the virus in a month, for example
- wtallis 1 year ago
- Sakos 1 year ago
- sulam 1 year agoJust keep in mind, dose-dependence is variable. It’s not a virus, but even one cryptosporidium oocyst is enough to get you sick.
- zby 1 year agoIf 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.
- XorNot 1 year agoNo this is all statistics again: probability that a viral particles survives in the body, probability that it successfully enters the cell (this is all chemical kinetics so it's not 100%), probability the cell survives long enough to replicate the virus, probability of an immune response picking up the lyzed cell immediately and then repeat for the daughter copies.
An analogous process would be human fertilization: it technically only takes 1 sperm to fertilize an egg, but it's millions in order to make the probability of it happening meaningfully high enough.
Of course some viruses are stupidly good at this: it's estimated 5 norovirus particles will trigger a full blown infection.
- XorNot 1 year ago
- 3seashells 1 year agoA 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.
- BenjiWiebe 1 year agoSources? Has this worked for you? Maybe this is something I'll try.
- 3seashells 1 year ago
- urbandw311er 1 year ago“Later analyses have shown this might not have been true”
- urbandw311er 1 year ago
- 3seashells 1 year ago
- BenjiWiebe 1 year ago
- swayvil 1 year agoThere 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.
- roywashere 1 year agoWhen I was sixteen I sailed a lot on the lakes in my neighborhood. I was strong and healthy and thought: what could microbes do against 1 meter 90 of me? So I drank the water from the lake to see what would happen. I became rather sick to my stomach :-) and I considered defeat
- yjftsjthsd-h 1 year agoThe claim was increased resilience, not perfect immunity.
- smegsicle 1 year agoabout how much lakewater are we talking
- yjftsjthsd-h 1 year ago
- angst_ridden 1 year agoBeing in excellent health can increase the required pathogen dose, and help resist illness. It can also, paradoxically, cause worse results. See, for example, “cytokine storm.”
- brewdad 1 year agoFor Covid, yes. If we look at the 1918 flu pandemic, the worst affected populations were those young adults with strong immune systems. They basically went into overdrive and the bodies attempts to fight the infection caused irreparable damage to the host.
- user_7832 1 year agoWhy is this downvoted? Hygiene and exercise is sound advice that any doctor'd agree with.
- extrememacaroni 1 year agoProbably because the poor guy's theory isn't true for all possible cases ever, isn't peer reviewed etc.
- dbsights 1 year agoI think the portraits of the downvoters would fully explain this phenomenon
- extrememacaroni 1 year ago
- roywashere 1 year ago
- thenerdhead 1 year ago> 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.
- HocusLocus 1 year agoJust one if it's a big one
- PaulKeeble 1 year agoLast 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.
- amanaplanacanal 1 year agoVentilation changes seem like a big deal. Unfortunately that requires businesses and government to spend money, instead of putting the burden on individuals. This would require regulatory action, and at least in the US we have important culture wars to fight instead.
- amanaplanacanal 1 year ago
- 1 year ago
- uuuuuuuiiiiii 1 year ago[dead]
- uuuuuuuiiiiii 1 year ago[dead]