Relief worker Josue Zurita became the second person to die in the devastated city after bacteria in the flood water enter a wound.
The 31-year-old had been helping repair homes left damaged after Houston was hit by Hurricane Harvey when a wound on his upper arm became seriously infected.
Infectious disease specialist Dr Philip Keiser said: “It’s most likely this person’s infection occurred when bacteria from Harvey debris or floodwater entered his body through a wound or cut.”
Mr Zurita was told he had necrotising fasciitis which destroys soft tissue, the Galveston County Health District said in a statement.
Relatives told the local media: “He’s a very caring person.
“He has a lot of friends here in Galveston that love him. Everybody is very sad. He was very young and always smiling.”
The deadly flood waters are thought to be the source of the infection which claimed its first victim recently.
Nancy Reed, 77, the infection after she fell and broke her arm in her flooded home.
A county medical examiner confirmed the bacteria enter her body through cuts.
Texas Department of State Health Services spokesman said they were aware of “at least two” flesh-eating bacteria deaths from the Harvey.
Residents are advised to clean wounds and cover them quickly with dry bandages to gift the fast-spreading infection.
Anyone exposed to flood waters should look out for symptoms that include warms skin, painful swelling, fever, chills and fatigue.
Dr Keiser said: “This is a very rare infection, but that doesn’t make it any less heartbreaking for this person’s family and friends.”