Trends in STDs in the United States



Chlamydia Positivity among 15- to 24-Year-Old Women Tested in Family Planning Clinics, by State, 1999 Chlamydia is the most commonly reported infectious disease in the United States and may be one of the most dangerous sexually transmitted diseases among women today. While the disease can be easily cured with antibiotics, millions of cases go unrecognized. If left untreated, chlamydia can have severe consequences, particularly for women. Up to 40 percent of women with untreated chlamydia will develop pelvic inflammatory disease (PID), and one in five women with pid becomes infertile. Chlamydia also can cause prematurity, eye disease, and pneumonia in infants. Moreover, women infected with chlamydia are three to five times more likely to become infected with HIV, if exposed. Seventy-five percent of women and 50 percent of men with chlamydia have no symptoms. The majority of cases therefore go undiagnosed and unreported. The number of reported cases-about 660,000 cases in 1999-is merely the tip of the iceberg.

A Closer Look at Chlamydia 

  • Chlamydia Positivity among 15- to 44-Year-Old Women Tested in  Family Planning Clinics, by hhs Regions, 1999An estimated three million people contract chlamydia each year (Cates, 1999).

  • Chlamydia is believed to be declining overall in the United States, primarily because of increased efforts to screen and treat women for chlamydia. Chlamydia is estimated to have declined from well over four million annual infections in the early 1980s to the current level of three million annual infections (Cates, 1999).

  • Reported chlamydia rates in women greatly exceed those in men largely because screening programs have been primarily directed at women.True rates are probably far more similar for women and men.

  • Since 1994, there has been increased funding available for chlamydia screening in publicly funded family planning and STD clinics. The percentage of women testing positive for
    chlamydia-chlamydia positivity-in family planning clinics by state provides a good indication of where the disease remains most wide-spread. The highest level of infection tends to be seen in areas where screening and treatment have not been as widely implemented. The greatest declines have generally been in areas of the country with the most effective and prolonged screening programs.

  • From 1988 to 1999, the Pacific northwest-Washington, Oregon, Idaho, and Alaska-witnessed a 62 percent decline in infection among women tested for chlamydia in family planning clinics.

  • In the Mid-Atlantic States-Delaware, Washington, D.C., Maryland, Pennsylvania, Virginia, and West Virginia-similar trends are occurring, with a decline of 16 percent since 1994
    (DSTDP, CDC, 2000).

  • From 1997 to 1999, chlamydia test positivity in family planning clinics actually increased in eight out of 10 regions. However, these reported increases are most likely due to changes in newly available and better laboratory tests and expanded screening programs to populations with higher levels of disease (DSTDP, CDC, 2000). Reducing the level of chlamydia will require continued expansion of screening and treatment among women and new efforts to reach men. While men experience symptoms and seek treatment on their own more often than women, half of men with chlamydia are asymptomatic. Reaching these men with treatment is critical to stem the spread of chlamydia and its severe consequences. It is also critical to reach those at greatest risk, primarily young people, with programs to help
    reduce their risk of infection through safer sexual behaviors.


A Closer Look at Chlamydia 

Chlamydia is widespread among the sexually active population, regardless of race, ethnicity, age, or gender. It is more concentrated among adolescents than any other STD with the highest rates seen among female adolescents. Data on male adolescents also reveal an alarming level of infection.


Forty percent of chlamydia cases are reported among young people, 15 to 19 years old. Reported prevalence among sexually active women is consistently more than five percent, with prevalence among teenage girls often exceeding 10 percent more than one in 10. And while the data are more limited for men, studies of adolescent males tested in high schools and other settings have found prevalence of more than five percent (Cohen, 1998; Ku, 1997). Recent studies and screening programs in multiple settings throughout the country come to the same conclusion: chlamydia continues to exact a devastating toll among our nation's young people.

  • In 1999, nearly 10 percent (9.9 percent) of 17- to 37-year-old women screened for STDs during their induction into the Army tested positive for chlamydia ( DSTDP, CDC, 2000).

  • In 1999, 7.2 percent of 15- to 24-year-old females screened in selected prenatal clinics in 22 states were positive for chlamydia ( DSTDP, CDC , 2000).

  • In 1999, of adolescent women entering juvenile detention facilities where chlamydia screening was routine, 13 percent tested positive for chlamydia ( DSTDP, CDC, 2000). 

  • A 1999 school-based screening program among high school students-ninth to twelfth grade in New Orleans found that nearly 12 percent of girls and six percent of boys were infected with chlamydia (Cohen, 1999).

  • A 1994 household sample of young men 18 to 19 years of age in three Maryland counties found that six percent were infected with chlamydia (Ku, 1996).

  • An innovative program in Denver screened high-risk youth in the field-parking lots, parks, and homes-and in non-clinical settings-high schools, recreation centers. The study found a high prevalence of chlamydia among young men-12 percent-screened in the field, compared to young men screened in the facilities 4.4 percent. The study suggests that the prevalence of chlamydia may be much higher among high-risk youth, who are not likely to access STD treatment in traditional health care settings (Rietmeijer, 1997).


Chlamydia is common among all races and ethnic groups, but prevalence is somewhat higher among racial and ethnic minorities, most likely due to the lack of access to screening and treatment programs.

  • Data from a pilot household survey of prevalence in ten U.S. counties suggests that chlamydia is widespread. And while prevalence was higher among young minority women, high levels of chlamydia were detected among all adolescents (Mertz, 1999).

  • The prevalence of chlamydia was higher in women than in men among African Americans (seven percent vs. six percent), Mexican Americans (five percent versus two percent), and whites (two percent versus one percent).
  • Among male and female teens, 15 to 19 years old, prevalence was approximately 12 percent for African Americans, six percent for Mexican Americans, and nearly four percent for whites.


Chlamydia prevalence remains higher in areas without longstanding screening and treatment programs. The highest rates are reported in the southern states. In 1999, seven out of the 10 states with the highest rates were located in the southern region of the United States. If the level of screening and treatment continues to increase, the disease will most likely decline in women across the nation.

This report is from the United States Department of Health and Human Services (US DHHS), Centers for Disease Control and Prevention (CDC), National Center for HIV, STD and TB Prevention (NCHSTP), web site (at and at as of July 6, 2004.
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This page last reviewed: Tuesday, November 19, 2019
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