In a surprising development, the number of teenagers engaging in sex dropped substantially in the 1990s, federal health officials reported Thursday.
"It is truly good news for all of us involved in the lives of America's teenagers," Health and Human Services Secretary Donna Shalala said in a statement.
The latest trends represent a departure from the increasing rates of sexual intercourse among adolescents that began in the 1970s and continued into the 1980s, according to a report released by the federal Centers for Disease Control and Prevention.
From 1991 to 1997, the share of the nation's teenagers who engaged in sexual activity declined 11%, CDC said. Last year, 48.4% of students in grades 9 through 12 were sexually active, the CDC said, compared with 54.1% in 1991.
"For the first time in a decade, less than half of the nation's high school students have engaged in sexual intercourse," said Lloyd Kolbe of the CDC's National Center for Chronic Disease Prevention and Health Promotion. "This is a very important milestone: It now lets them say that they are in the majority."
The results, some experts said, could demonstrate that teaching students about sex and safe-sex practices does not result in an increase in promiscuity, as critics had feared.
Also, students who said they had sex during the last three months reported a 23% increase in condom use, from 46.2% of students in 1991 to 56.8% in 1997, the agency said.
The latest findings were based on national, state and local surveys conducted among more than 50,000 students during the 1990s. The students completed written questionnaires asking them about a range of sexual activity.
The study contrasts with another published in May in the journal Science, which found that sex and other risky behaviors may be more prevalent among teenage boys than they admit in standard questionnaires. In the Science study, teenagers answered questions via computer.
Kolbe attributed the drop to numerous prevention strategies, among them the widespread inclusion of classroom sex education in schools across the nation and the growing intervention of churches, local organizations and, most important, "more family discussions around the dinner table between parents and their children."
"This is a very important set of data. It's the first time we've seen this kind of decrease," Kolbe said. "We've been very quick to criticize our young people in recent decades as we've watched this percentage increase, and I believe it is just as important to commend them as we watch it decline."
Percentages of high school students who reported ever having sexual intercourse range from 38% in ninth grade to 60.9% in 12th grade. This compares with the 1991 figures of 39% for grade 9 and 66.7% for grade 12, the CDC said.
The overall percentage of sexually experienced teenage males decreased from 57.4% in 1991 to 48.8% in 1997, CDC said, whereas sexually active females decreased from 50.8% to 47.7%.
The trend toward abstinence contrasts with the promiscuity of the 1970s and '80s, when sexual activity ballooned among teenagers, Kolbe said. Sexual activity among girls 15 to 19, for example, jumped from 29% in 1970 to 57% in 1988, according to previous studies.
CDC said the decreases in sexual activity were also paralleled by declines in teenage pregnancy and gonorrhea, a sexually transmitted disease. Decreasing sexual behavior also reduces the danger of contracting other serious infections, such as AIDS, CDC said.
About 3 million sexually transmitted diseases occur annually among teenagers, and up to 1 million girls become pregnant. Teen pregnancy rates, however, decreased significantly from 1992 to 1995 in those 42 states with available data, the CDC said.
But health officials and others warned against becoming too complacent.
"As with almost every social ill, education once again proves to be the best antidote," said Daniel Zingale, executive director of AIDS Action.
He called for greater efforts to reach dropouts and youths past high school age. Half of all new HIV infections occur in people younger than 25, he said.
"Clearly, this is not a one-shot deal, and no single approach will effectively reach all teens," said Dr. Helene Gayle of the CDC.