Some illnesses and harmful infections are caused by bacteria. these bacteria grow in the human body and often make people sick with symptoms like coughing, sneezing, and fever. these illnesses are not related to any genetic mutations or other problems with dna.

why would gene therapy fail to cure illnesses caused by bacteria?

gene therapy reduces symptoms but never cures illnesses.
gene therapy does not work on most people.
gene therapy only focuses on replacing mutated genes.
gene therapy is too long a process.