Why is someone considered no longer contagious after a few days on antibiotics?
In: Biology
Someone is no longer contagious after the immune system has overwhelmed the bacterial infection, which antibiotics help to occur rapidly. That might be a few days after antibiotics start… or it might not happen, or it might have already happened and the antibiotics were unnecessary. There’s no magic time interval that always applies for every person, every infection, and every antibiotic.
Because the infection is nearly entirely gone. The rest of the antibiotics are to ensure total eradication to prevent the creation of antibacterial resistant strains.
Slowly increasing concentration of antibiotics (by for example only running a few days of antibiotics and then needing treatment again) massively increases the likelihood of a resistant strain- repeat for a few cycles (possibly in different people if infected) and you have a whole resistant infection to that antibiotic. A full treatment makes sure it goes all the way from 0 to 100% concentration and kills the entire infection – making it much less likely a microbe could randomly mutate resistance in one go
[here](https://youtu.be/plVk4NVIUh8?si=tkadHS_SkGs-2dhW) is a Harvard video demonstrating how increasing concentration can speed up resistance. I recall an experiment like this juxtaposed against one that went straight from 0 to 1000 but haven’t been able to find- the result was that no microbe managed to evolve resistance to 1000x concentration in one go
I described the immune system like this in another sub, and I think it is fitting here as well.
Think of it like a fruit stand in a market square. The immune system knows that people will come up and want apples, oranges and mangoes, so they stock apples, oranges and mangoes. This is how the body handles the day to day exposure. Every so often someone comes by and asks for a pineapple, but when they find out they can’t get one, they leave (exposure to a small amount of a new virus or bacteria).
Problems happen when a lot of people want pineapples. They start chanting, form a mob and pretty soon there is a full on riot of people asking for pineapples and there are more coming every minute. Pretty soon these mobs want to travel to other places to find pineapples (transmission). The immune system can get pineapples, but it’s going to take some time (creating antibodies). Because it’s an all out riot, it needs some extreme measures. It calls in the riot police (inflammatory response). The riot police are very aggressive and cause a lot of damage along the way, sometimes more than the rioters themselves. Antibiotics are like calling in the army special forces. They hunt down and kill anyone who says pineapple. Unfortunately, this also means sometimes some poor cell says “what’s a pineapple?” and gets blown away (side effects).
Once the riot has been stopped (infection managed), the fruit stand now has pineapples, but there is a lot of cleanup to do. Broken windows, smashed fruit, flipped cars and a lot of bodies. This is the post-infectious period. The body is still repairing the damage. The riot has stopped and there are almost no rioters left, but the damage remains (why you still feel sick).
Even after everything has gone back mostly to normal, there may still be a few rioters around, hiding in bathrooms and closets. They want chaos and want to start a riot. The army (antibiotics) are still around, hunting for them. This is why to take antibiotics until the end of the prescription and not just until you feel better. If any rioters survive all of it, they’ve learned how to hide from the army. They still want to riot, so they’ll find another fruit stand to terrorize (antibiotic resistance). Pretty soon, some of these rioters can only be taken out by highly trained, very dangerous super secret special forces if they’ve learned the tactics of all the other army units (our “last resort” antibiotics).
Viruses can’t be killed by the army. They need pineapples and won’t go away until they get them. This is why we don’t use antibiotics in viral illnesses. Antiviral medications are more like a rapid air drop of pineapples and monoclonal antibodies are lab cloned pineapples we can inject or eat.
This depends a lot on what bacteria we’re talking about.
A single bacterium is not necessarily enough to cause an infection. It will more likely require many thousands. Depending on the disease, you will have more or less of them in your lungs at various stages.
All these criteria are based on studies. In these cases, studies have shown that after a certain period, there won’t be enough of the pathogen (or perhaps any) in your bodily fluids to cause infection in another person.
It’s not a black and white thing, it doesn’t mean everything is gone, it just means you couldn’t possibly get someone else sick, there just aren’t enough bacteria in your mucous. This would usually mean that the majority of them have been killed off, and the infection has dropped to a level that the total number is constantly reducing.
You may still have symptoms (immune reactions aren’t turned on and off instantaneously), but you won’t be a breeding ground anymore.
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