Sex diseases continue to rise in the US, and chlamydia and gonorrhea are the two most common diseases, latest data reveal.

The 1,030,911 cases of chlamydia in 2006 are the highest ever recorded for any nationally reported disease in any year, federal health officials said in releasing their annual report on sexually transmitted diseases. They said that because of underreporting, a more accurate estimate is 2.8 million new chlamydia cases annually.

About 19 million new cases of all kinds of sexually transmitted diseases occur in this country each year, but only the three are nationally reported. Genital herpes, papillomavirus and trichomonas infections account for the vast majority of cases, but doctors are not required to report them nationally.

Different reasons account for the rise of each of the three reportable and curable diseases, and for each a different approach is needed to reduce its incidence, Centers for Disease Control and Prevention, told reporters by telephone.

The three reported sexually transmitted diseases affect African-Americans disproportionately. The black to white ratios are gonorrhea 18 to 1, syphilis 6 to 1 and chlamydia 8 to 1, Dr. Douglas said in an interview. The reasons for the disparities are not clear. Lack of access to health care may be one problem.

“Chlamydia is now the most common S.T.D. ever reported,” Dr. John M. Douglas Jr., head of the division of sexually transmitted diseases at the Centers for Disease Control and Prevention, said.