(03-14) 04:00 PDT Seoul -- When South Korean children press their parents for an explanation on how babies are born, many moms and dads tell them they were found under a bridge, in the same way their American counterparts invoke the classic tale of the stork.

In South Korea, conservative mores discourage frank discussions about sex and some people say promiscuity and adultery are less common than in many other Asian countries.

"Most people don't have sex before marriage. It is just not accepted," said Min Ju Kim, a 24-year-old university student in Seoul, who like most single South Koreans lives at home. "My mother changes the (television) channel when people kiss."

Many health experts say society's renunciation of promiscuity is a major reason why South Korea's 50 million inhabitants have one of the lowest HIV infection rates in Asia. The United Nations HIV/AIDS agency (UNAIDS) says there were only 4,000 cases, or .01 percent of the 15-to-49 year age bracket, at the end of 2001.

But the outwardly conservative Korean culture is not always what it seems.

Some recent surveys show that 17 percent of high school students are sexually active. And since South Korea is a male-dominated society, many urban red-light areas resemble a huge "boy's club" -- bars outnumber other businesses; coin-fed punching bags and kicking machines test strength; Karaoke clubs called norae-bongs allow men to sing, drink and flirt with young women, and "barber shops" offer "massages."

Official statistics show that men account for nearly 89 percent of Koreans with HIV. Most are in their 30s, making up 35.2 percent of current cases, compared with 27.1 percent of men in their 20s. About 29 percent contracted the virus through homosexual activity.

About 94 percent of all South Koreans contracted the virus through sexual transmission, with 67 percent from heterosexual intercourse and 30 percent from homosexual intercourse, according to the National Institute of Health. Very few South Koreans contracted HIV through dirty needles.

The high percentage of men with HIV raises the seldom-discussed question of extramarital sex, which health experts say has become more prevalent in recent years.

Most men looking for affairs frequent commercial sex workers. An entrenched culture of prostitution traces its origins to the Japanese colonial period of 1910 to 1945, when prostitution was legal.

According to a recent study by the Korean Institute of Criminology, 358,000 men visit prostitutes daily at one of Korea's 5,000 illegal barber shops, steam baths, hotels, tea rooms and salons for businessmen. The study found that nearly 20 percent in the 20-to-64 age bracket purchase sex more than four times a month.

As in neighboring Japan, the sex industry in South Korea is big business, accounting for $20 billion, or 4.1 percent of the nation's total gross domestic product in 2002, just behind agriculture at 4.4 percent, according to the same report by the Korean Institute of Criminology.

Health officials say a thriving sex industry and a reluctance to talk about safe sex likely contributed to a steady increase in infections.

In 1997, the government recorded 124 new cases while in 2002, the number grew to 400, the largest increase since the first case was confirmed in 1985.

"We need to fight the sexual taboos and make it OK to talk about it," said Kwon Jun Wook, director of the National Institute of Health's Division of Communicable Disease Control.

The first known case, in 1985, was a South Korean prostitute who had sex mainly with U.S. servicemen. When other women from areas near U.S. bases tested HIV-positive in the late 1980s, they all had a specific virus now known as the "Korean strain." Health experts say a majority of AIDS cases in South Korea carry that strain.

Since then, U.S. servicemen and women are screened for HIV before they leave the United States. Once they arrive in South Korea, they are tested periodically, and any who test positive are sent home immediately.

Until 1990, health experts say every AIDS victim contracted the disease overseas or through contact with foreigners living here. But by 1993, the majority of new infections were passed from Korean to Korean.

Health officials say reluctance to use condoms, a rise in infections among homosexuals, an increase in young Koreans' sexual activities and lack of information about contraception are likely factors that could lead to a significant increase in HIV infections in future years.

"Korea needs to be shocked by someone famous with the disease, like the United States with Rock Hudson," said Kwon. "Maybe then parents will see the importance of talking about it at home."

The government now offers a Web site with AIDS information, a 24-hour hot- line and free AIDS tests. The National Institute of Health also plans to install 18,000 condom vending machines at major nightspots throughout the country and at "every possible location we can," said Kwon.

Recognizing the reluctance of parents to address AIDS, sexuality and especially contraception, a government campaign encourages middle school and high school teachers to lead candid discussions with their students about the consequences of unprotected sex.

Starting at the middle school level, students are taught about abstinence and safe sex practices. But critics say the depth of classroom discussions depends on the willingness of individual teachers to broach the subject. Students say some would rather show anatomical charts and tame videos than preside over a frank discussion.

Saets Byul Choi, a 16-year-old high school student from the industrial city of Ansan, just south of Seoul, recalled a recent video shown at her school.

"It was about a man and a woman who fall in love and get married. They get into the bed fully dressed and the screen goes black," she said. "When they return to the screen, the woman has a big stomach."

For Ji Suk Kang, a 16-year-old high school student from Seoul, the fuss over dangerous sexual practices is moot. Like many South Korean youths, she is wrapped up in her studies and has little time to worry about sexually transmitted diseases.

"I am so busy with school that I don't even have time for a boyfriend," she said.

Meanwhile, government officials talk about legalizing prostitution in an effort to control the flourishing industry. Their greatest fear is that foreign visitors who visit red-light districts could help spread the disease.

"Compared to other countries, South Korea has a low infection rate," said Kwon. "But as society becomes more liberal about sex, the rate is expected to climb."