Chlamydia is one of the most common but curable sexually transmitted diseases (STDs), and most people who are infected don’t know they have it. Estimates place the number of new infections in the U.S. at 3 million per year, mostly among those between the ages of 14 and 24.

Who is most likely to contract chlamydia, how has the infection been trending over the years, and where are cases most likely to occur in the United States?

What Is Chlamydia?

Chlamydia is an infection caused by the bacteria chlamydia trachomatis. Though most people who are infected remain asymptomatic, signs of chlamydia vary between men and women:

Men

  • Clear or cloudy discharge from tip of penis
  • Pain and swelling around testicles
  • Painful urination
  • Burning and itching on opening of penis

Women

  • Abnormal vaginal discharge
  • Painful periods
  • Painful urination
  • Itching or burning around vagina

Only about 1.7 million of the 3 million+ infections of chlamydia are actually reported to healthcare workers because so few people become symptomatic and get themselves tested. The only way to get chlamydia is through sexual contact because the bacteria travels through bodily fluids like semen, pre-cum and vaginal fluids.

It’s not possible to contract chlamydia through casual, non-sexual contact like sharing food or hugging. In rare cases, it’s possible to spread chlamydia to the eyes by touching the area with a hand or finger that’s got infected fluids on it.

Who Is Most Likely to Get Chlamydia?

Sexually active young people are at a very high risk of contracting chlamydia, and about two-thirds of new cases are in people between 15 and 24 years of age. Generally, women are much more likely than men to be diagnosed with chlamydia, though that distinction shifts as people age. Past age 40, more men than women have chlamydia.

Chlamydia infection rates by sex, age 15+ (cases per 100,000 people)

Age group Males Females
15–19 924.5 3,265.70
20–24 1,705.40 3,985.80
25–29 1,091.90 1,725.40
30–34 598.9 725.7
35–39 351.1 361.8
40–44 197.5 170.8
45–54 106.3 63.3
55–64 37.5 17.9
65+ 6.7 2.5
Total 363.1 687.4

Among racial groups, African-Americans are the most likely to be diagnosed with chlamydia.

Chlamydia infection rates by race, age 15+ (cases per 100,000 people)

African-American 1,175.80
Native American/Alaska Native 781.2
Native Hawaiian/Pacific Islander 715.40
Hispanic/Latino 404.1
White 211.3
Multiracial 162.9
Asian 129.6

Chlamydia Across the U.S.

The national chlamydia infection rate is 528.8 per 100,000 people, but that rate varies quite widely depending on the state in question. Alaska, for instance, has a rate more than 50% higher than that.

Chlamydia infection rate by state (cases per 100,000 people)

Alaska 799.8
Louisiana 742.4
Mississippi 707.6
New Mexico 651.6
South Carolina 649.8
Georgia 631.4
North Carolina 619.7
Alabama 615.5
New York 591.6
Illinois 589.9
Arkansas 579.6
Arizona 571.3
Delaware 566.3
California 557.4
Maryland 555.4
Oklahoma 554.4
Nevada 553.1
Texas 543.9
Missouri 536.4
Ohio 528.6
Tennessee 527.5
Indiana 516.8
South Dakota 512.7
Michigan 509.6
Virginia 503.7
Rhode Island 500
Connecticut 496.3
Colorado 487.2
Florida 485.2
Wisconsin 480
Hawaii 479.5
Kansas 466.2
Oregon 455.2
Nebraska 450.7
Iowa 443.2
Washington 442.2
Pennsylvania 441.5
Montana 437.4
Kentucky 435.4
North Dakota 432.5
Massachusetts 430.4
Minnesota 426.4
New Jersey 394
Idaho 368.4
Wyoming 365.8
Maine 342.1
Utah 332.2
New Hampshire 330.5
Vermont 297.5
West Virginia 226.1
Total 528.8

Most states have seen their infection rates for chlamydia go up over the past half-decade, and several states have seen rather large increases that exceed 25%.

Percentage change in chlamydia infection rates (cases per 100,000 people), 2013-2017

West Virginia -18%
Hawaii 1%
Vermont 1%
Alabama 1%
Delaware 1%
Alaska 2%
Wyoming 6%
North Dakota 7%
Pennsylvania 8%
Idaho 9%
South Dakota 10%
Arkansas 11%
New Mexico 11%
Texas 11%
Michigan 12%
Kentucky 12%
Tennessee 13%
Nebraska 15%
Ohio 15%
Montana 16%
Wisconsin 17%
Oklahoma 17%
Florida 18%
Louisiana 19%
Illinois 19%
Missouri 19%
New York 21%
South Carolina 21%
Mississippi 21%
Indiana 21%
Rhode Island 22%
Minnesota 23%
Maryland 23%
Kansas 23%
Massachusetts 24%
Arizona 24%
New Jersey 24%
Washington 24%
Georgia 24%
Iowa 25%
Virginia 25%
Oregon 26%
North Carolina 26%
Colorado 26%
Utah 28%
California 28%
Nevada 31%
Maine 32%
New Hampshire 40%
Connecticut 40%

In addition to major variation based on the state in question, several cities and metro areas have far higher rates than other cities across the country. Among selected major metropolitan areas, Memphis has the highest of all rates.

Chlamydia rates by metro area (cases per 100,000 population)

Memphis, TN-MS-AR 872.6
Virginia Beach-Norfolk-Newport News, VA-NC 785.9
New Orleans-Metairie, LA 776.3
Milwaukee-Waukesha-West Allis, WI 775
Indianapolis-Carmel-Anderson, IN 683.6
Cleveland-Elyria, OH 670
Richmond, VA 668
Birmingham-Hoover, AL 643.9
Charlotte-Concord-Gastonia, NC-SC 642.6
Philadelphia-Camden-Wilmington, PA-NJ-DE-MD 636.9
Austin-Round Rock, TX 632.9
San Diego-Carlsbad, CA 627.9
Chicago-Naperville-Elgin, IL-IN-WI 623.8
San Antonio-New Braunfels, TX 600.1
Baltimore-Columbia-Towson, MD 599
Oklahoma City, OK 597
San Francisco-Oakland-Hayward, CA 595.2
Jacksonville, FL 592.8
Atlanta-Sandy Springs-Roswell, GA 590.5
Los Angeles-Long Beach-Anaheim, CA 588.3
St. Louis, MO-IL 586.7
Columbus, OH 583.9
Buffalo-Cheektowaga-Niagara Falls, NY 581.2
Phoenix-Mesa-Scottsdale, AZ 577.9
Orlando-Kissimmee-Sanford, FL 568.1
Detroit-Warren-Dearborn, MI 564.9
Kansas City, MO-KS 563.9
New York-Newark-Jersey City, NY-NJ-PA 559.7
Raleigh, NC 555.9
Louisville-Jefferson County, KY-IN 552.1
Las Vegas-Henderson-Paradise, NV 551.9
Denver-Aurora-Lakewood, CO 544
Sacramento-Roseville-Arden-Arcade, CA 540.3
Washington-Arlington-Alexandria, DC-VA-MD-WV 540.3
Riverside-San Bernardino-Ontario, CA 536.5
Houston-The Woodlands-Sugar Land, TX 528.7
Cincinnati, OH-KY-IN 517.5
Dallas-Fort Worth-Arlington, TX 515.2
Hartford-West Hartford-East Hartford, CT 509.8
Miami-Fort Lauderdale-West Palm Beach, FL 485.1
Nashville-Davidson-Murfreesboro-Franklin, TN 478.6
Tampa-St. Petersburg-Clearwater, FL 478.6
Minneapolis-St. Paul-Bloomington, MN-WI 475.9
Portland-Vancouver-Hillsboro, OR-WA 472.6
Seattle-Tacoma-Bellevue, WA 469.4
Salt Lake City, UT 465
Providence-Warwick, RI-MA 432.1
San Jose-Sunnyvale-Santa Clara, CA 398.1
Boston-Cambridge-Newton, MA-NH 380.3
Pittsburgh, PA 333

Today, reported chlamydia rates are the highest they’ve ever been in the United States, with a more than 10% increase in the rate of cases in just the past couple of years and a huge increase when zooming even further out.

Chlamydia rates by year (cases per 100,000 population)

1984 6.5
1985 17.4
1986 35.2
1987 50.8
1988 87.1
1989 102.5
1990 160.2
1991 179.7
1992 182.3
1993 178
1994 192.5
1995 187.8
1996 190.6
1997 205.5
1998 231.8
1999 247.2
2000 251.4
2001 274.5
2002 289.4
2003 301.7
2004 316.5
2005 329.4
2006 344.3
2007 367.5
2008 398.1
2009 405.3
2010 423.6
2011 453.4
2012 453.3
2013 443.5
2014 452.2
2015 475
2016 494.7
2017 528.8

Conclusion

Chlamydia rates have risen in the U.S. by nearly 20% in just the past five years, illustrating just how dangerous this STD can be. Often a silent infection, chlamydia can cause pain and discomfort in the rare cases when those infected do have symptoms. But perhaps the worst risk of chlamydia is when it goes untreated and leads to serious health complications. As many as 15% of women with untreated chlamydia go onto develop pelvic inflammatory disease, which can affect a woman’s overall health and ability to reproduce.

The good news is chlamydia is very easily treated and cured with medication, but the first step is finding out your status. If you are among those most likely to have chlamydia (sexually active and under 30), it’s time to get tested.

Additional References

  • Centers for Disease Control and Prevention, Table 2. Chlamydia — Reported Cases and Rates of Reported Cases by State, Ranked by Rates, United States, 2017. (2018). Retrieved from https://www.cdc.gov/std/stats17/tables/2.htm
  • Centers for Disease Control and Prevention, Table 10. Chlamydia — Reported Cases and Rates of Reported Cases by Age Group and Sex, United States, 2013–2017. (2018). Retrieved from https://www.cdc.gov/std/stats17/tables/10.htm
  • Centers for Disease Control and Prevention, Table 1. Sexually Transmitted Diseases — Reported Cases and Rates of Reported Cases per 100,000 Population, United States, 1941–2017. (2018). Retrieved from https://www.cdc.gov/std/stats17/tables/1.htm