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Comment by ars | Hacker News Reader

> is partial treatment

I've never understood this, maybe you can answer me. Doesn't the immune system also kill bacteria? By using antibiotics you kill most of the bacteria, and then the immune system finishes them off.

After all, if any bacteria were left wouldn't they just get the person sick again?

An infection starts with just a few bacteria, a reinfection would be the same - unless the immune system keeps them in check, in which case there are no bacteria left to build resistance.

If a bacteria is resistant then giving the full does wouldn't help anyway, it's resistant after all. It won't do anything except remove all competition so the resistant will be the only bacteria left. It seems to me it's better to try to kill only some of the bacteria so you don't isolate the resistant one so well, and rely on the immune system to kill most of the bacteria.

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On the last bit, resistance isn't a binary switch. If you assume a spectrum, then day 1 kills all the really easy bacteria. By day 4 of 8, you've killed the 85% most killable bacteria, and your symptoms are gone, so you stop. Then you have leftover bacteria that your immune system may or may not be able to handle, but you can still pass it to someone else who doesn't have an immune system primed to fight it off, so their infection starts with the 85th percentile bacteria.

(all numbers arbitrary)

That just makes my question stronger! So why continue the antibiotic till you create bacteria at the 98th percentile?

Stop the antibiotic as early as possible.

It's not like you're going to wait to infect people till you're done with the antibiotic, so the "starts with the 85th percentile" scenario still happens. But by taking even more antibiotic all you do (as far as I can tell) is make even more resistant bacteria.

One reason I can think of is that most Antibiotics do not only kill bacteria, they also stall bacterial growth.

So while the most resistant bacteria are killed at last, they still might not be able to multiply.

Because now you have ten times as many resistant bacteria going out into the world. They are marginally less resistant but they are still resistant, and you have so many more of them.

I'm reaching the end of my knowledge, but I would guess that there's a good tradeoff between reducing the number down to 2% vs culling down to the "best" remainder. You also give your immune system more time to catch up and take car of the rest for you. If you can, with antibiotics, kill off 98% and prevent growth over a week, you immune system can probably handle the rest and you transfer 0 to the next person.

'resistant' isn't the same as 'totally unaffected by' - it's a spectrum, and the duration of treatment is one of the factors which determines how much of that spectrum is killed. At the 'I feel better now' stage, there could still be quite a large population that would still be killed by completing the course of treatment.

One function of the immune system is killing bacteria, but it can also quarantine and reject (e.g: Phlegm, vomiting, etc) them, which is one source of transmission.

> there could still be quite a large population that would still be killed by completing the course of treatment.

That's perfect! That means if you stop there then what you have left is un-resistant bacteria. That's excellent, you avoided breeding resistance.

So why do you want to keep taking antibiotics that narrows down the bacteria till only resistant ones are left?

You're still breeding resistance, just slightly slower.

In the best case, the full treatment kills all of them, or enough that your immune system can eliminate them completely. Resistance doesn't develop because it doesn't get a chance. They're all dead.

Worst case, you kill enough to weed out those with no or weak resistance, and then spread the infection to others where it can continue to evolve.

So it comes down to (a) how much are you concentrating/selecting for these resistances, and (b) how likely are you to pass it on such that it propagates.

I think it's reasonable to assume that a lower bodily population makes it less likely to pass on, which would be one good reason. Another might be that, by heavily reducing the population, you may reduce the genetic diversity enough that they're susceptible to other factors (ie: when not facing antibiotics, they get starved out by the non-resistant strains because the resisting mutations come with costs attached). By leaving a larger population alive, there's more scope for hybridisation leading to overall stronger species.

I must admit I have little formal knowledge in this area, so it's possible these effects don't exist, or have only limited impact. If I had time it would be interesting to look into it further, it seems like this topic is too obvious not to have been considered before.

The body does finish them off in a way. They wall off areas of the lung for example, making "tubercles", that contain tissue and latent bacteria.

Future ill health allow these to reactivate.

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