Prevention is better than therapy-Correct my mistakes in this brief article

I'll be happy if you guys correct mistakes of below passage whether grammatical or dictation and so ... .

Prevention is better than therapy ,
nowadays this issue has been proven to everyone that prevention has always been better than therapy . The biggest problem in the world of medical science has been the contagious of the HIV virus , mostly among black people throughout the world .

many infected people has been a large number of various experiments by medical scientists .
today in spite of scientist's warning about dangerous influence of not using condoms in sexual relation , some people has been seen to be defiant about the importance of using the condom and its vital roll in prevention of HIV virus .

"Prevention is better than therapy nowadays. This issue has been proven to everyone that prevention has always been better than therapy. (How?) The biggest problem in the world of medical science has been the contagious HIVvirus, mostlyamong black people throughout the world.Where did you get this information? Where is the citation to support it?

M any infected people have been in a large number of various experiments by medical scientists. Where is your source for this information? People infected with what? What kinds of "various" medical experiments?I n spite of scientists' warnings about the dangerous consequences of not using condoms in sexual relations , some people seem to be defiant about the importance of using condoms and their vital roll in the prevention of the HIV virus. "

Hi Gloria . thanks for your feedback .
actually i didn't want to focus on details . my intention was just to find my grammatical weaknesses that you did help me and i appreciate for it .

when i review my passage and your suggestions , i find out most of my mistakes are on detail and resource that i didn't care of them .

I'll send more essays on this forum and i hope to learn something more of you friends .