That's not quite the case with our brewing, you can usually isolate the source of the infection, be it a scratch in our gear, some piece of biomatter lodged somewhere and replace the gear/hoses, "carpet bomb" the rest of the gear with a bleach water solution, and switch up your sanitizer for awhile, and that will take care of it usually. I know from experiece.
And besides, despite most new brewer's fear of infections, they are actually inevitable, and are really no big deal.
There is a lot of info in this thread.
https://www.homebrewtalk.com/f39/has-anyone-ever-messed-up-batch-96644/
I hate to break it to you, but it's inevetable that you will have a bad batch or infection somewhere down the line...On Craftbrewer radio they said it usually happens around the 10th, the 30th and the 50th batch...even the pro's deal with it (the Brewer at New Glarus said in an interview on Basicbrewing radio that a commercial brewery operation gets a 3 year grace period before their first infection)
It's called a house germ...and it develops over time...
I got an infection around the 20th batch, I replaced my autosiphon, bottling wand and all my hoses and changed my sanitizer, in case the house germ was getting used to it...
This is one of the best posts on the subject....
The hosts of the podcast in Australia have 60 years of brewing experience...It's funny, but John Palmer
learns from them they've been doing hpmebrewing radio for 6-7 years first on commercial than as a podcast...this is a very good discussion on infection and infection control.
They talk about the "timeframe" of infections, and how it is less likely for a first batch to be infected...it tends to occur around the 10th batch and the 50th...When the equipment gets more used up, and "house germs" start to build up. They used the term "house mouth" in the discussion, how we may not even notice, because we're sort of used to the taste of our beers, it's usually NOT a regular drinker of our beers that notices it.
So really, if it happens it's not the end of the world....but most people need to realize, especially new brewers that infections are still relatively rare, especially if it is your first batch of beer, and you gear is relatively new. Someone like me with several year old gear is more likely going to get a scratch or slip somewhere and get one.
But after I found the source of mine (in my autosiphon) I replaced it, got new hoses, thoroughly cleaned everything, and began alternating between Starsan and iodophor to keep ahead of any germs...I haven't had any more issues in a year.