Hello,
A "letter of intent", also called a "personal statement", "statement of interest", or something similar, is supposed to be written BY YOU to express YOUR interest in pursuing the degree. While there may be agencies out there that will write one for you for a fee, this would be considered dishonest, and probably not terribly effective in securing your admission to a good school. (In fact, they could probably revoke your admission if they discovered that your application had been partially ghostwritten.)
If I have misunderstood, and you simply want feedback or editorial/proofreading assistance on a letter of intent that you are writing, I would recommend asking a colleague, particularly one who has attended graduate school or medical school in the U.S. or Canada (assuming that is where you are planning to apply). The people who post to this bulletin board often give helpful advice as well if you have specific questions about what to include or not include, or about the programs at particular schools.
It is important that you write something that explains why you are applying to public health programs, what about your professional background or interests has led you to apply, how you hope to use the MPH education and degree to reach your professional goals, and in what area you plan to focus your research. The schools will look for evidence of scholarly maturity, motivation, and a high likelihood that you will complete the degree program and make a contribution in your chosen area of public health.
Please post again if you have additional questions, and good luck with your applications.
