Sexually transmitted infections are on the rise, putting more people at risk as they spread. Chlamydia rates have nearly doubled since 2000, while the rate of gonorrhea went up by 50% over the same period. The Centers for Disease Control and Prevention reports that syphilis rates are reaching levels last seen in the 1950s.
But some regions of the U.S. are seeing higher rates than others.
Stacker used CDC data to look at which counties reported the highest rate of sexually transmitted infections in Colorado. Counties are ranked by the rate of chlamydia infections, the most prominent STI at the national level, with gonorrhea and then syphilis rates serving as tiebreakers. This story focuses on bacterial infections, which can be cured, rather than viral infections such as HIV and herpes. At the county level, 2021 cases are the most recent available from the CDC, but state and national-level data for 2022 are also included. This story focuses on sexual transmissions and does not include congenital syphilis cases that were inherited from the mother.
Condoms are the most effective way to prevent the spread of STIs for people with multiple sexual partners, but research has found a decreasing rate of condom use among straight, bisexual, and gay male populations.
During the HIV/AIDS epidemic throughout the 1980s and 1990s, public health efforts advocating for condom use helped curb the spread of the virus. Today, however, condoms are no longer the only tool. Pills such as PrEP lower the risk of contracting HIV from sex by as much as 99%.
While more recent data is not available, the latest CDC survey from 2011-2015 showed less than half of unmarried men used condoms during the last time they had sex.
Among high school students having sex, the share using condoms has fallen from 60% in 2011 to 52% in 2021. While one-third of sexually active students used hormonal birth control, only 10% used both condoms and birth control. Methods like the pill and IUDs are effective at preventing pregnancy but do not stop the spread of STIs.
Chlamydia, gonorrhea, and syphilis are technically bacterial infections—meaning they can be cured with antibiotics—but they can still have lasting health impacts, including pelvic inflammatory disease and infertility. These risks are heightened when left untreated, which many STIs are as they don't obviously present themselves.
The CDC recommends annual testing for cisgender women, transgender men, and gender-nonconforming people with cervixes. It also recommends annual testing for males with male sexual partners. People in these groups who frequently have sex with anonymous partners should be tested every three to six months. Anyone with symptoms should always get tested according to the guidelines.
The CDC says there is little evidence that screening among straight men lowers the spread, and the agency's limited budget is put towards programs benefiting the most at-risk groups. However, some public health groups advocate for testing among all people regardless of sex and sexual orientation.
Data from the National Survey of Family Growth shows men on average have more opposite-sex sexual partners than women, and some argue that catching STIs throughout a sexual network rather than just for the most at-risk groups could curb their spread.
Soon, a pill may also help counter the spread of STIs. DoxyPEP can be taken 24 to 72 hours after unprotected sex and stops an STI before it becomes spreadable and symptomatic. The CDC has shared proposed guidelines recommending it for men who have sex with men and transgender women. The drug was originally approved for treating inhalation of anthrax, and doctors can prescribe it for off-label use.
Read on to see how STI infection rates in Colorado compare nationally, and the top counties.
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Emma Rubin // Stacker
1 / 51State-level statistics
- Chlamydia cases: 456.3 per 100K (#31 nationally, 26,646 cases)
- Gonorrhea cases: 150.4 per 100K (#29 nationally, 8,784 cases)
- Primary and secondary syphilis cases: 15.7 per 100K (#25 nationally, 918 cases)
#50. San Miguel County
- Chlamydia cases: 136.2 per 100K people (11 case)
- Gonorrhea cases: 24.8 per 100K people (2 cases)
- Syphilis cases (non-congenital): 12.4 per 100K people (1 case)
--- Primary and secondary syphilis: 0 cases
--- Nonprimary and nonsecondary early syphilis: 12.4 per 100K people (1 case)
#49. Teller County
- Chlamydia cases: 136.4 per 100K people (34 cases)
- Gonorrhea cases: 48.1 per 100K people (12 cases)
- Syphilis cases (non-congenital): 4.0 per 100K people (1 case)
--- Primary and secondary syphilis: 4.0 per 100K people (1 case)
--- Nonprimary and nonsecondary early syphilis: 0 cases
#48. Baca County
- Chlamydia cases: 142.3 per 100K people (5 cases)
- Gonorrhea cases: 227.7 per 100K people (8 cases)
- Syphilis cases (non-congenital): 0 cases
--- Primary and secondary syphilis: 0 cases
--- Nonprimary and nonsecondary early syphilis: 0 cases
#47. Kit Carson County
- Chlamydia cases: 143.9 per 100K people (10 cases)
- Gonorrhea cases: 43.2 per 100K people (3 cases)
- Syphilis cases (non-congenital): 0 cases
--- Primary and secondary syphilis: 0 cases
--- Nonprimary and nonsecondary early syphilis: 0 cases
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#46. Cheyenne County
- Chlamydia cases: 175.7 per 100K people (3 cases)
- Gonorrhea cases: 0 cases
- Syphilis cases (non-congenital): 0 cases
--- Primary and secondary syphilis: 0 cases
--- Nonprimary and nonsecondary early syphilis: 0 cases
#45. Ouray County
- Chlamydia cases: 178.7 per 100K people (9 cases)
- Gonorrhea cases: 0 cases
- Syphilis cases (non-congenital): 0 cases
--- Primary and secondary syphilis: 0 cases
--- Nonprimary and nonsecondary early syphilis: 0 cases
#44. Lincoln County
- Chlamydia cases: 193.4 per 100K people (11 case)
- Gonorrhea cases: 52.7 per 100K people (3 cases)
- Syphilis cases (non-congenital): 0 cases
--- Primary and secondary syphilis: 0 cases
--- Nonprimary and nonsecondary early syphilis: 0 cases
#43. Douglas County
- Chlamydia cases: 198.4 per 100K people (732 cases)
- Gonorrhea cases: 49.1 per 100K people (181 case)
- Syphilis cases (non-congenital): 8.1 per 100K people (30 cases)
--- Primary and secondary syphilis: 3.5 per 100K people (13 cases)
--- Nonprimary and nonsecondary early syphilis: 4.6 per 100K people (17 cases)
#42. Clear Creek County
- Chlamydia cases: 201.1 per 100K people (19 cases)
- Gonorrhea cases: 116.5 per 100K people (11 case)
- Syphilis cases (non-congenital): 0 cases
--- Primary and secondary syphilis: 0 cases
--- Nonprimary and nonsecondary early syphilis: 0 cases
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#41. Routt County
- Chlamydia cases: 211.2 per 100K people (53 cases)
- Gonorrhea cases: 43.8 per 100K people (11 case)
- Syphilis cases (non-congenital): 8.0 per 100K people (2 cases)
--- Primary and secondary syphilis: 4.0 per 100K people (1 case)
--- Nonprimary and nonsecondary early syphilis: 4.0 per 100K people (1 case)
#40. Pitkin County
- Chlamydia cases: 213.3 per 100K people (37 cases)
- Gonorrhea cases: 46.1 per 100K people (8 cases)
- Syphilis cases (non-congenital): 23.1 per 100K people (4 cases)
--- Primary and secondary syphilis: 23.1 per 100K people (4 cases)
--- Nonprimary and nonsecondary early syphilis: 0 cases
#39. Grand County
- Chlamydia cases: 214.4 per 100K people (34 cases)
- Gonorrhea cases: 25.2 per 100K people (4 cases)
- Syphilis cases (non-congenital): 6.3 per 100K people (1 case)
--- Primary and secondary syphilis: 6.3 per 100K people (1 case)
--- Nonprimary and nonsecondary early syphilis: 0 cases
#38. Yuma County
- Chlamydia cases: 221.3 per 100K people (22 cases)
- Gonorrhea cases: 0 cases
- Syphilis cases (non-congenital): 0 cases
--- Primary and secondary syphilis: 0 cases
--- Nonprimary and nonsecondary early syphilis: 0 cases
#37. Gunnison County
- Chlamydia cases: 225.7 per 100K people (39 cases)
- Gonorrhea cases: 17.4 per 100K people (3 cases)
- Syphilis cases (non-congenital): 5.8 per 100K people (1 case)
--- Primary and secondary syphilis: 0 cases
--- Nonprimary and nonsecondary early syphilis: 5.8 per 100K people (1 case)
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#36. Saguache County
- Chlamydia cases: 231.8 per 100K people (15 cases)
- Gonorrhea cases: 30.9 per 100K people (2 cases)
- Syphilis cases (non-congenital): 0 cases
--- Primary and secondary syphilis: 0 cases
--- Nonprimary and nonsecondary early syphilis: 0 cases
#35. Crowley County
- Chlamydia cases: 232.9 per 100K people (14 cases)
- Gonorrhea cases: 49.9 per 100K people (3 cases)
- Syphilis cases (non-congenital): 33.3 per 100K people (2 cases)
--- Primary and secondary syphilis: 16.6 per 100K people (1 case)
--- Nonprimary and nonsecondary early syphilis: 16.6 per 100K people (1 case)
#34. Fremont County
- Chlamydia cases: 243.7 per 100K people (121 case)
- Gonorrhea cases: 46.3 per 100K people (23 cases)
- Syphilis cases (non-congenital): 22.2 per 100K people (11 case)
--- Primary and secondary syphilis: 18.1 per 100K people (9 cases)
--- Nonprimary and nonsecondary early syphilis: 4.0 per 100K people (2 cases)
#33. Broomfield County
- Chlamydia cases: 256.2 per 100K people (193 cases)
- Gonorrhea cases: 94.3 per 100K people (71 case)
- Syphilis cases (non-congenital): 17.3 per 100K people (13 cases)
--- Primary and secondary syphilis: 8.0 per 100K people (6 cases)
--- Nonprimary and nonsecondary early syphilis: 9.3 per 100K people (7 cases)
#32. Delta County
- Chlamydia cases: 259.0 per 100K people (82 cases)
- Gonorrhea cases: 69.5 per 100K people (22 cases)
- Syphilis cases (non-congenital): 3.2 per 100K people (1 case)
--- Primary and secondary syphilis: 0 cases
--- Nonprimary and nonsecondary early syphilis: 3.2 per 100K people (1 case)
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#31. Huerfano County
- Chlamydia cases: 260.1 per 100K people (18 cases)
- Gonorrhea cases: 57.8 per 100K people (4 cases)
- Syphilis cases (non-congenital): 14.5 per 100K people (1 case)
--- Primary and secondary syphilis: 14.5 per 100K people (1 case)
--- Nonprimary and nonsecondary early syphilis: 0 cases
#30. Jefferson County
- Chlamydia cases: 261.1 per 100K people (1,513 cases)
- Gonorrhea cases: 100.8 per 100K people (584 cases)
- Syphilis cases (non-congenital): 14.7 per 100K people (85 cases)
--- Primary and secondary syphilis: 9.7 per 100K people (56 cases)
--- Nonprimary and nonsecondary early syphilis: 5.0 per 100K people (29 cases)
#29. Montrose County
- Chlamydia cases: 278.0 per 100K people (120 cases)
- Gonorrhea cases: 132.0 per 100K people (57 cases)
- Syphilis cases (non-congenital): 13.9 per 100K people (6 cases)
--- Primary and secondary syphilis: 9.3 per 100K people (4 cases)
--- Nonprimary and nonsecondary early syphilis: 4.6 per 100K people (2 cases)
#28. Montezuma County
- Chlamydia cases: 294.2 per 100K people (77 cases)
- Gonorrhea cases: 122.3 per 100K people (32 cases)
- Syphilis cases (non-congenital): 11.5 per 100K people (3 cases)
--- Primary and secondary syphilis: 3.8 per 100K people (1 case)
--- Nonprimary and nonsecondary early syphilis: 7.6 per 100K people (2 cases)
#27. Moffat County
- Chlamydia cases: 295.8 per 100K people (39 cases)
- Gonorrhea cases: 91.0 per 100K people (12 cases)
- Syphilis cases (non-congenital): 30.3 per 100K people (4 cases)
--- Primary and secondary syphilis: 22.8 per 100K people (3 cases)
--- Nonprimary and nonsecondary early syphilis: 7.6 per 100K people (1 case)
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#26. La Plata County
- Chlamydia cases: 296.9 per 100K people (167 cases)
- Gonorrhea cases: 88.9 per 100K people (50 cases)
- Syphilis cases (non-congenital): 23.1 per 100K people (13 cases)
--- Primary and secondary syphilis: 16.0 per 100K people (9 cases)
--- Nonprimary and nonsecondary early syphilis: 7.1 per 100K people (4 cases)
#25. Summit County
- Chlamydia cases: 300.6 per 100K people (93 cases)
- Gonorrhea cases: 58.2 per 100K people (18 cases)
- Syphilis cases (non-congenital): 9.7 per 100K people (3 cases)
--- Primary and secondary syphilis: 3.2 per 100K people (1 case)
--- Nonprimary and nonsecondary early syphilis: 6.5 per 100K people (2 cases)
#24. Phillips County
- Chlamydia cases: 310.3 per 100K people (14 cases)
- Gonorrhea cases: 22.2 per 100K people (1 case)
- Syphilis cases (non-congenital): 22.2 per 100K people (1 case)
--- Primary and secondary syphilis: 22.2 per 100K people (1 case)
--- Nonprimary and nonsecondary early syphilis: 0 cases
#23. Bent County
- Chlamydia cases: 312.6 per 100K people (18 cases)
- Gonorrhea cases: 69.5 per 100K people (4 cases)
- Syphilis cases (non-congenital): 0 cases
--- Primary and secondary syphilis: 0 cases
--- Nonprimary and nonsecondary early syphilis: 0 cases
#22. Eagle County
- Chlamydia cases: 314.0 per 100K people (175 cases)
- Gonorrhea cases: 25.1 per 100K people (14 cases)
- Syphilis cases (non-congenital): 9.0 per 100K people (5 cases)
--- Primary and secondary syphilis: 5.4 per 100K people (3 cases)
--- Nonprimary and nonsecondary early syphilis: 3.6 per 100K people (2 cases)
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Bob Pool // Shutterstock
31 / 51#21. Logan County
- Chlamydia cases: 325.8 per 100K people (70 cases)
- Gonorrhea cases: 69.8 per 100K people (15 cases)
- Syphilis cases (non-congenital): 4.7 per 100K people (1 case)
--- Primary and secondary syphilis: 0 cases
--- Nonprimary and nonsecondary early syphilis: 4.7 per 100K people (1 case)
#20. Larimer County
- Chlamydia cases: 326.6 per 100K people (1,184 cases)
- Gonorrhea cases: 91.3 per 100K people (331 case)
- Syphilis cases (non-congenital): 8.3 per 100K people (30 cases)
--- Primary and secondary syphilis: 3.6 per 100K people (13 cases)
--- Nonprimary and nonsecondary early syphilis: 4.7 per 100K people (17 cases)
#19. Garfield County
- Chlamydia cases: 334.6 per 100K people (208 cases)
- Gonorrhea cases: 74.0 per 100K people (46 cases)
- Syphilis cases (non-congenital): 4.8 per 100K people (3 cases)
--- Primary and secondary syphilis: 3.2 per 100K people (2 cases)
--- Nonprimary and nonsecondary early syphilis: 1.6 per 100K people (1 case)
#18. Lake County
- Chlamydia cases: 351.0 per 100K people (26 cases)
- Gonorrhea cases: 67.5 per 100K people (5 cases)
- Syphilis cases (non-congenital): 13.5 per 100K people (1 case)
--- Primary and secondary syphilis: 0 cases
--- Nonprimary and nonsecondary early syphilis: 13.5 per 100K people (1 case)
#17. Mesa County
- Chlamydia cases: 351.5 per 100K people (553 cases)
- Gonorrhea cases: 125.2 per 100K people (197 cases)
- Syphilis cases (non-congenital): 5.7 per 100K people (9 cases)
--- Primary and secondary syphilis: 3.2 per 100K people (5 cases)
--- Nonprimary and nonsecondary early syphilis: 2.5 per 100K people (4 cases)
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#16. Conejos County
- Chlamydia cases: 354.7 per 100K people (27 cases)
- Gonorrhea cases: 92.0 per 100K people (7 cases)
- Syphilis cases (non-congenital): 0 cases
--- Primary and secondary syphilis: 0 cases
--- Nonprimary and nonsecondary early syphilis: 0 cases
#15. Otero County
- Chlamydia cases: 355.0 per 100K people (66 cases)
- Gonorrhea cases: 75.3 per 100K people (14 cases)
- Syphilis cases (non-congenital): 16.1 per 100K people (3 cases)
--- Primary and secondary syphilis: 5.4 per 100K people (1 case)
--- Nonprimary and nonsecondary early syphilis: 10.8 per 100K people (2 cases)
Maciej Bledowski // Shutterstock
38 / 51#14. Boulder County
- Chlamydia cases: 355.9 per 100K people (1,173 cases)
- Gonorrhea cases: 93.5 per 100K people (308 cases)
- Syphilis cases (non-congenital): 10.3 per 100K people (34 cases)
--- Primary and secondary syphilis: 6.4 per 100K people (21 case)
--- Nonprimary and nonsecondary early syphilis: 3.9 per 100K people (13 cases)
#13. Las Animas County
- Chlamydia cases: 382.7 per 100K people (56 cases)
- Gonorrhea cases: 129.8 per 100K people (19 cases)
- Syphilis cases (non-congenital): 13.7 per 100K people (2 cases)
--- Primary and secondary syphilis: 0 cases
--- Nonprimary and nonsecondary early syphilis: 13.7 per 100K people (2 cases)
#12. Rio Grande County
- Chlamydia cases: 412.0 per 100K people (47 cases)
- Gonorrhea cases: 87.7 per 100K people (10 cases)
- Syphilis cases (non-congenital): 8.8 per 100K people (1 case)
--- Primary and secondary syphilis: 8.8 per 100K people (1 case)
--- Nonprimary and nonsecondary early syphilis: 0 cases
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#11. Weld County
- Chlamydia cases: 420.8 per 100K people (1,431 case)
- Gonorrhea cases: 128.5 per 100K people (437 cases)
- Syphilis cases (non-congenital): 9.4 per 100K people (32 cases)
--- Primary and secondary syphilis: 6.5 per 100K people (22 cases)
--- Nonprimary and nonsecondary early syphilis: 2.9 per 100K people (10 cases)
#10. Morgan County
- Chlamydia cases: 444.7 per 100K people (129 cases)
- Gonorrhea cases: 179.3 per 100K people (52 cases)
- Syphilis cases (non-congenital): 20.7 per 100K people (6 cases)
--- Primary and secondary syphilis: 17.2 per 100K people (5 cases)
--- Nonprimary and nonsecondary early syphilis: 3.4 per 100K people (1 case)
#9. Costilla County
- Chlamydia cases: 469.0 per 100K people (17 cases)
- Gonorrhea cases: 303.4 per 100K people (11 case)
- Syphilis cases (non-congenital): 27.6 per 100K people (1 case)
--- Primary and secondary syphilis: 0 cases
--- Nonprimary and nonsecondary early syphilis: 27.6 per 100K people (1 case)
#8. El Paso County
- Chlamydia cases: 485.6 per 100K people (3,583 cases)
- Gonorrhea cases: 174.7 per 100K people (1,289 cases)
- Syphilis cases (non-congenital): 9.6 per 100K people (71 case)
--- Primary and secondary syphilis: 6.2 per 100K people (46 cases)
--- Nonprimary and nonsecondary early syphilis: 3.4 per 100K people (25 cases)
#7. San Juan County
- Chlamydia cases: 545.7 per 100K people (4 cases)
- Gonorrhea cases: 136.4 per 100K people (1 case)
- Syphilis cases (non-congenital): 0 cases
--- Primary and secondary syphilis: 0 cases
--- Nonprimary and nonsecondary early syphilis: 0 cases
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#6. Adams County
- Chlamydia cases: 558.5 per 100K people (2,916 cases)
- Gonorrhea cases: 201.5 per 100K people (1,052 cases)
- Syphilis cases (non-congenital): 24.1 per 100K people (126 cases)
--- Primary and secondary syphilis: 14.9 per 100K people (78 cases)
--- Nonprimary and nonsecondary early syphilis: 9.2 per 100K people (48 cases)
#5. Arapahoe County
- Chlamydia cases: 562.8 per 100K people (3,686 cases)
- Gonorrhea cases: 246.6 per 100K people (1,615 cases)
- Syphilis cases (non-congenital): 25.7 per 100K people (168 cases)
--- Primary and secondary syphilis: 14.8 per 100K people (97 cases)
--- Nonprimary and nonsecondary early syphilis: 10.8 per 100K people (71 case)
#4. Pueblo County
- Chlamydia cases: 575.4 per 100K people (976 cases)
- Gonorrhea cases: 275.3 per 100K people (467 cases)
- Syphilis cases (non-congenital): 71.9 per 100K people (122 cases)
--- Primary and secondary syphilis: 50.1 per 100K people (85 cases)
--- Nonprimary and nonsecondary early syphilis: 21.8 per 100K people (37 cases)
#3. Alamosa County
- Chlamydia cases: 616.4 per 100K people (102 cases)
- Gonorrhea cases: 169.2 per 100K people (28 cases)
- Syphilis cases (non-congenital): 12.1 per 100K people (2 cases)
--- Primary and secondary syphilis: 12.1 per 100K people (2 cases)
--- Nonprimary and nonsecondary early syphilis: 0 cases
#2. Prowers County
- Chlamydia cases: 633.5 per 100K people (76 cases)
- Gonorrhea cases: 158.4 per 100K people (19 cases)
- Syphilis cases (non-congenital): 0 cases
--- Primary and secondary syphilis: 0 cases
--- Nonprimary and nonsecondary early syphilis: 0 cases
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f11photo // Shutterstock
51 / 51#1. Denver County
- Chlamydia cases: 932.7 per 100K people (6,636 cases)
- Gonorrhea cases: 490.0 per 100K people (3,486 cases)
- Syphilis cases (non-congenital): 68.2 per 100K people (485 cases)
--- Primary and secondary syphilis: 38.7 per 100K people (275 cases)
--- Nonprimary and nonsecondary early syphilis: 29.5 per 100K people (210 cases)
This story features data reporting and writing by Emma Rubin and is part of a series utilizing data automation across 49 states.
