The prevalence of symptomatic chlamydial infection in patients who visit medical facilities has been documented, but the number of asymptomatic patients, accounting for the majority of infected individuals, remains unclear. Although increasing concern has been expressed about the spread of infection among teenagers due to a drop in age at which individuals become sexually active, epidemiological information continues to be insufficient. Large scale screening research on asymptomatic chlamydial infection targeting young subjects including high school students has been initiated. This paper focuses on, (1) research on university and technical school students prior to large-scale research and (2) large-scale research targeting high school students will be explained. The frequency of infection in teenagers and prevention based on research results described using results of this research.
The prevalence of chlamydial infection in sexually active male and female university and special technical school students aged 18 years or older who are asymptomatic was 8.3%(female 9.1%, male 7.0%). By age, the prevalence of chlamydial infection in 18 to 19-year-old females was 13.4%, suggesting that the rate of teenage infection is serious. The spread of infection among high school students, the majority of teenagers, is an urgent concern, lending impetus to large-scale research targeting high school students.
In a screening of 5, 000 high school students, the prevalence of asymptomatic chlamydial infection became apparent for the first time. Prevalence of the infection is 13.1% among female high school students and 6.6% among male high school students, leaving no doubt of the presence of epidemic infection among teenagers. The prevalence of infection was 3.9% in the United States (female high school students in California in 2003) and 2.1% in Sweden (female high school students in Uppsala in 1994). Infection in Japan thus appears to be expanding fastest among developed countries.
Research results suggest that concrete measures required are (1) targeting of teenagers for epidemic prevention;(2) implementation of measures for epidemic prevention based on data including gender, age, and risk factors; and (3) quick action in cooperation with government agencies, regional medical associations, and individuals involved in school education.

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The high prevalence of asymptomatic sexually transmitted infections in Japan have become a serious public health problem especially Chlamydia trachomatis infection in young women. On the other hand, it was reported that asymptomatic C. trachomatis infection was found in young healthy men at the rate of several percentage. To estimate the prevalence of asymptomatic sexually transmitted infections in young healthy men in Japan, we determine this study. Two hundred and four volunteers were recruited. The first voided urine specimens and cotton swab wiping of the external genitalia were used for detection of C. trachomatis, Neisseria gonorrhoeae and HPV. The participants asked to respond to a self-administered questionnaire for information about sexual behavior as the frequency of sexual intercourse, number of current sex partners. The prevalence were 3.4% for C. trachomatis and 5.9% for HPV. No N. gonorrhoeae was detected. In sexually active men who had regular sexual intercourse, the detection rate of C. trachomatis was 4.7% and that of HPV was 8.0%. The study showed that the prevalence of asymptomatic infections in young healthy men were not negligible.

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In order to prevent the spread of sexually transmitted diseases (STDs) among teenagers, we investigated the prevalence of STDs among female teenagers who visited our adolescent clinic in 2003. We have been conducting lectures at the high schools in Gunma prefecture since 1993. In addition, we investigated the relationship between the sexual behavior of the teenagers and their family environment. Among the 194 female patients who visited our adolescent clinic in 2003, 54 (28%) had STDs; chlamydial infection in 27 cases (50%), candidiasis in 19 cases (35%), cervical dysplasia in 5 cases (9%), condyloma acuminatum and trichomonas vaginal infection in 2 cases (3.7%) each, and gonococcal infection and genital herpes in one case (1.9%) each. The infection rates with Chlamydia trachomatis and Neisseria gonorrhoeae in 2004 were reduced to 66.5% and 69.7% as compared with those in 2001. As for the influence of the family environment on the sexual behavior of the children, the incidence of indulgence in sexual activities was higher among children who felt unhappy in their family than among those who felt happy. From these results, we consider that it is important to increase the level of awareness of teenagers and their families about STDs to prevent the spread of STDs among teenagers.

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Ten percent of junior-high school pupils and 40% of high school pupils have initial sexual intercourse in Japan. However, only half of them use condom, therefore, the prevalence of sexually transmitted diseases (STDs) and the risk of unexpected pregnancy are high in Japanese teenagers. Disappointingly, the movement against condom campaign for teenagers or the law of sales limitation of condom for teenagers are present. The most effective tool of condom campaign is the TV commercial of condom. However, TV commercials of condom are self-regulated in Japan, and these circumstances do not contribute condom campaign. On the other hand, the usefulness of condom use for the prevention of STDs is described in the textbook of junior-high school. In addition, the details of appropriate condom use are described with some photographs in the textbook of high school. It is very important to give teenagers impression and sympathy to condom. One's sexual partners, who do not use condom because it is bothersome or uncomfortable, are unsympathetic to one with the explanation quoting the Mother Teresa's word “The opposite of love is indifference”.

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