Your GRE, GPA, and research experience makes you a strong candidate. Have you looked at which schools you would be interested in applying to? Being interested in several areas is not really a bad thing. On the contrary, it gives you many options. If you have a potential list of school you are interested in, I think the best strategy would be to tailor your statement to match the research interests of that school in areas that are strongest in that school. Research programs focus on developing skills and techniques in scientific methodology. You can write about your interest in gaining these skills and what you would like to do with a PhD. Also, you can something like " Community health is a broad area and encompasses several areas such as substance abuse, tobacco control, reproductive health, violence prevention, and obesity. I think that in the face of complexity we face in this discipline, it would ineffective to specialize too narrowly." or you can express your intention of choosing your area of emphasis as you progress through the fist year. Hope this helps.