Dr. Judith Wasserheit, director of the STD Prevention Program at the Centers for Disease Control and Prevention, said Tuesday that the figures were in line with researchers' expectations.
At the same time, she said: "That's a substantial portion of the population and it's probably a low-end estimate."
Also, gonorrhea cases are rising again, especially among young people, after nearly two decades of decline, while syphilis is at an all-time low, CDC officials said Tuesday at the National STD Prevention Conference in Milwaukee.
The human papilloma virus causes more than 95 percent of cervical cancer cases, with the HPV-16 strain accounting for half of them, Wasserheit said.
Black women ages 20 to 29 had the highest rates of HPV-16 infection, at 36 percent. Overall, 19.1 percent of blacks carry the strain, compared with 12.5 percent of whites, according to the study led by CDC researcher Dr. Katherine Stone.
An estimated 20 million Americans carry genital HPV infections that can be passed on through sexual contact, and there are about 5.5 million new infections every year. HPV, which also causes genital warts and penile and anal cancer, is the most common STD among sexually active young people, Wasserheit said.
Condoms can reduce the risk of spreading the virus, but it can be transmitted through even minor cuts in the skin.
Overall, more than 65 million Americans are infected with one or more sexually transmitted diseases. There are an estimated 15 million new infections annually, a quarter of them among teen-agers.
Gonorrhea infections went up 9 percent between 1997 and 1999, with rates increasing among young people, gay and bisexual men and blacks, Wasserheit said. About 360,000 new cases are reported each year, but the actual numbers are believed to be twice as high, Wasserheit said.
"This is one of the key diseases for our young people. This is crazy. We've got to do better on this," she said.
Researchers said one reason for the increase is that less attention is being paid to gonorrhea because of the heavy focus on AIDS.
Southern states had the highest rates.
"This is directly related to issues of poverty and inadequate access to quality health care and preventive services," said Dr. Ronald Valdiserri, deputy director of the National Center for HIV, STD and TB Prevention at the CDC.
Gonorrhea, a curable bacterial disease, can cause pelvic inflammatory disease and infertility if untreated in women. Having it also raises the risk of transmitting or becoming infected with the AIDS virus.
Syphilis is at an all-time low, with reported 6,157 reported cases in 1999, an 88 percent decrease from 1990. The disease dropped 29 percent between 1997 and 1999 among blacks, wnt up 20 percent among Hispanics and was relatively stable among whites.
Baltimore, which had the nation's highest rate of syphilis, cut its rate of infection 63 percent since 1997.
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