A 13 year old young boy that I watch with my grandkids 3 days a week just found out he has a SEVERE UTI?

I knew girls and women get these but I have only ever heard of a man gewtting it one time when My husband was messing around with a Nasty . He got an infection from her nasty body. But this boy is 13 NOT AULLY ACTIVE. Unless he is messing with his mother or my granddaughters. Because other than my house, his other grandparents about 8 mile out in the country or Home he is never allowed to go any place. When I have him Monday, Wednesday and Fridays I make sure he drinks Tea and Water and has a lot of Liquids to help keep them Hydrated from being HOT outside. I do Not Allow them Soda at my house. I do Not feel Soda is something a Child need. I do not allow them Candy and Sweets. I do not eat them myself. I buy fruit juice popcycles when They get them. Only sugar they get at my house is On their 1 bowl of Cereal of a morning. Rest of the day is Chees Tortillas for a snack. Or Chicken Nuggets and French fries from Scratch. Real potatoes cut up and chicken dipped in Flour and cooked. We do not do fast food resturants. But he woke up yesterday running a high fever and vomiting and complaining his stomach hurt so his mother took him to the ER. The Doctor told him he has a Severe Urinary Track Infection. My grandkids asked what caused him to get it. I told them could be him not cleaning himself or Wearing Dirty Clothes. Not taking showers. My grandson said he wears his boxer shorts 2 or 3 days at a time and only showers once a week when he is made to.