Rare in the UK since our hygiene got so good, but common in the third world, and seen in UK people who have been abroad.
Gold standard is stool, blood or urine culture. However, transaminases (LFTs) may be raised.
It's quite resistant these days, so the standard has become fluroquinolones - commonly ciprofloxacin - with steroids if that isn't working.
Treated, about 1-5% die, untreated more like 15%. 5% go on to become chronic carriers as the organism hides in the gall bladder.