How credible do you think typhoid fever is, and how much of it seems like embroidery?

I think "Typhoid Fever", which is part of frank McCourt's memoir, is very credible. He shows the world through the eyes of his young self as he understands it. In the narrative, the influence of religion in Ireland at that time is felt in every sphere of life and so is the anti-British sentiment. Moreover, he uses different regional accents for the characters to give it a more authentic feel.

By it's very nature, any creative work would have some imaginative aspects in it. Possibly, the jokes or the way the scenes unfold have some embellishments to it but the overall experience is very real.