( CNN ) -- One look at her photo , and you ca n't help but ask : How could someone so young and vibrant die so quickly from an infection ? Brazilian model Mariana Bridi da Costa died from a sepsis infection . Brazilian model Mariana Bridi da Costa was a healthy 20-year-old when doctors told her she had a urinary tract infection , her family says . The infection spread , and after amputating her feet , doctors thought they had the situation under control , according to a blog run by a family friend . `` She 's alive , [ she ] will survive , '' Renato Lindgren wrote on the blog on January 20 , before da Costa also had to have her hands amputated , and part of her stomach and both kidneys extracted . `` She can eat well , visit the sea , swim , travel , talk with her friends and family , marry and have a baby . She has a full and beautiful life ahead . '' Four days later , da Costa was dead . Sepsis -- the body 's inflammatory response to an infection -- really can kill that quickly , according to Dr. Kevin Tracey , author of a book about sepsis called `` Fatal Sequence : The Killer Within . '' `` This is n't a one in a million case , '' says Tracey , chief executive officer of the Feinstein Institute for Medical Research in Manhasset , New York . `` When an infection reaches a certain point , this can happen in a matter of hours . '' Sepsis usually starts out as an infection in just one part of the body , such as a skin wound or a urinary tract infection , Tracey says . For example , Muppets creator Jim Henson died in 1990 from a case of sepsis that started out as pneumonia , an inflammation of the lungs . He was 53 . Most of the time , simple , localized infections remain just that : easy to treat and in one part of the body . Why some infections rage out of control and shut down vital organs is a mystery , but experts say it rarely happens in young , healthy people , like da Costa . Watch more on avoiding septicemia » . `` You can ask , 'Why her ? ' but really no one knows why her , '' Tracey says . `` It might have something to do with her immune system . It might be about her genetics . '' The Mayo Clinic sees about 100 cases a year of young , healthy people who develop sepsis , says Dr. Priya Sampathkumar , an infectious disease specialist at Mayo . With treatment , which usually involves antibiotics and sometimes draining of the wound , about 75 percent survive . Sampathkumar says the key is to keep an eye on even such simple infections as a small skin wound . A fever , a dramatic shift in blood pressure , rapid breathing and extreme confusion are all signs that someone needs quick medical help , she says . `` You need to watch it , '' she says . Dr. Carl Flatley said he had no idea what to watch for when his 23-year-old daughter , Erin , developed sepsis in 2002 . He says she went into the hospital for a minor hemorrhoid procedure and five days later was dead from sepsis . `` It 's a horrible death , '' he says . Two years later , knowing the signs of sepsis saved his own life , says Flatley , a dentist in Dunedin , Florida . He fell ill , and an emergency room doctor said he had a urinary tract infection and sent him home . But Flatley said he suspected it was much more than a UTI . `` I felt very sick . My testicle was sore . I told him I was concerned I had sepsis and I refused to go home . He got very irritated with me , '' Flatley says . But in the end , Flatley was admitted to the hospital , where the infection had become so severe that doctors were forced to remove his right testicle . Flatley started The Sepsis Alliance to educate others about sepsis , where he tries to walk a fine line . `` You do n't want to panic people . We all get infections and , thank God , most of them heal , '' he says . `` So this is what I tell people : If you 're feeling bad all over and have a high temperature and either high or low blood pressure , those are all indications that your whole system has been infected . It could be sepsis . '' He advises getting medical help immediately , and to specifically mention that you 're concerned you might have sepsis . `` You do n't want to take any chances , '' he says . CNN 's Jennifer Pifer-Bixler and Sabriya Rice and CNN Español 's Cibele Lorenzoni contributed to this report .
Brazilian woman Mariana Santos - Costa , 24 , died after sepsis had spread . Sepsis starts as infection in one part of body , then rages out of control . Fever , big shift in blood pressure , rapid breathing , mental instability are red flags .