got this from a website written by a christian worried about the growth of islam:

Note that Muslim population growth maybe driven by other factors than their choice to have more children. Because Muslims are not as promiscuous as the rest of the human race they have largely avoided AIDS. While there is some danger that most of a generation in some sub-Sahara countries will die of AIDS, the rate of infection in Muslim countries is typically less than one in a thousand adults. If large numbers of non-Muslims die of AIDS and Muslims do not then the precentage of the world's population that is Muslim will increase.

But AIDS is only one of many Venereal diseases that afflict humanity. If Muslims have avoided AIDS it is a pretty good guess that they have also avoided the others, and it maybe a good guess that AIDS is only one of the medical problems plaguing sub-Sahara Africa. Some of those veneral diseases, like hepatitis C (which I know can be spread by other means) are deadly.

Other veneral diseases, particularly gonorrhea and chlamydia, do not kill but they do cause infertility. I have heard that infertility is far less common in Egypt than America. While about twenty percent of American couples are infertile only ten percent of Egyptian couples are.

In defense of Islam and the Muslims it might be noted that the venerial plagues that are afflicting the world are not their fault. Promiscuous people not only spread venereal diseases they also provide the environment in which new ones evolve. On the other hand, if most of the world's population becomes Muslim some venereal diseases might become extinct.

http://www.geocities.com/richleebruce/b/islam.html