There is new(ish) evidence emerging that recurrent UTIs, also known as chronic cystitis, are not always caused by a reinfection with a new pathogen but rather can be a relapse of the same pathogen.
It turns out that pathogenic bacteria have the ability to invade the cells of the bladder and live there in a dormant sleep-like state.
This is called an ‘intracellular bacterial community’.
In this state, the bacteria remain undetected by standard urine testing and unaffected by antibiotic treatment. They also remain undetected by our own immune system.
Now and again they can leave the cells, causing a relapse of the urinary tract infection.