At least 250 million sexually transmitted infections occur worldwide annually and the growing epidemic is creating "a public health nightmare," the World Health Organization reported Wednesday.

Young adults account for the largest share of the 250 million infections, with the highest incidence reported among people ages 20 through 24, WHO said."Sexually transmitted infections and diseases have reached epidemic proportions globally. And if sexual behavior is not modified and effective new prevention and control programs are not implemented immediately, the resulting disease and mortality rates will be even more staggering," WHO Director General Dr. Hiroshi Nakajima warned.

WHO emphasized that diseases spread by sex are not harmless and can cause serious health problems, such as sterility, blindness, brain damage, cancer and even death. In addition, there is evidence the sores and inflammation caused by sexually transmitted infections boosts the risk of contracting the deadly AIDS virus during sex.

Trichomoniasis, a parasitic infection, is the most common sexually transmitted infection - making up about 120 million of the 250 million new cases that occur each year. About 50 million cases stem from chlamydia, a bacterial infection that can cause infertility.