Nov. 22, 2010 -- With gonorrhea rates down to an all-time low, chlamydia has become the top reported STD in the U.S., the CDC's annual STD report shows.

About 2.8 million Americans get chlamydia each year, the CDC estimates. That's why the national health agency considers the 19% increase in reported cases since 2006 to be good news: It means more people are getting tested.

Perhaps the really good news in the annual report is that gonorrhea rates dropped to 99 cases per 100,000 Americans -- the lowest rate since the CDC started tracking the disease in 1945.

But syphilis cases continue to spiral upward:

There were 5% more syphilis cases in the past year and a whopping 39% more cases since 2006.

Syphilis is down among women but skyrocketing among men who have sex with men.

More than half of all syphilis cases reported in 2009 were among African-Americans, including a tripling of syphilis cases among young black men aged 15 to 24.

The racial disparity seen with syphilis is also seen with chlamydia and gonorrhea:

Gonorrhea rates in African-Americans is 20 times higher than in white Americans and 10 times higher than in Hispanic Americans.

Young black women aged 15-24 bear the heaviest gonorrhea burden among Americans.

Chlamydia rates in African-Americans are eight times higher than in white Americans and three times higher than in Hispanic Americans.

"A range of factors contributes to these disparities, including poverty, lack of access to health care, and an already high prevalence of STDs in communities of color that increases a person's risk of infection with each sexual encounter," the CDC notes in a fact sheet accompanying the annual report.

Screening detects STDs before they cause permanent damage to the body -- and prevents further spread of infection. Yet fewer than half of people who should be screened do so. All sexually active people should get regular STD screening.