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 California. 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 California compare nationally, and the top counties.
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Emma Rubin // Stacker
1 / 51State-level statistics
- Chlamydia cases: 493.6 per 100K (#22 nationally, 192,647 cases)
- Gonorrhea cases: 205.6 per 100K (#18 nationally, 80,257 cases)
- Primary and secondary syphilis cases: 20.1 per 100K (#19 nationally, 7,849 cases)
#50. El Dorado County
- Chlamydia cases: 185.8 per 100K people (359 cases)
- Gonorrhea cases: 52.8 per 100K people (102 cases)
- Syphilis cases (non-congenital): 12.9 per 100K people (25 cases)
--- Primary and secondary syphilis: 6.2 per 100K people (12 cases)
--- Nonprimary and nonsecondary early syphilis: 6.7 per 100K people (13 cases)
StephanieFarrell // Shutterstock
3 / 51#49. Tuolumne County
- Chlamydia cases: 186.3 per 100K people (104 cases)
- Gonorrhea cases: 87.8 per 100K people (49 cases)
- Syphilis cases (non-congenital): 19.7 per 100K people (11 case)
--- Primary and secondary syphilis: 19.7 per 100K people (11 case)
--- Nonprimary and nonsecondary early syphilis: 0 cases
#48. Plumas County
- Chlamydia cases: 190.8 per 100K people (38 cases)
- Gonorrhea cases: 30.1 per 100K people (6 cases)
- Syphilis cases (non-congenital): 10.0 per 100K people (2 cases)
--- Primary and secondary syphilis: 10.0 per 100K people (2 cases)
--- Nonprimary and nonsecondary early syphilis: 0 cases
CL Shebley // Shutterstock
5 / 51#47. Glenn County
- Chlamydia cases: 197.9 per 100K people (57 cases)
- Gonorrhea cases: 86.8 per 100K people (25 cases)
- Syphilis cases (non-congenital): 20.8 per 100K people (6 cases)
--- Primary and secondary syphilis: 20.8 per 100K people (6 cases)
--- Nonprimary and nonsecondary early syphilis: 0 cases
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#46. Placer County
- Chlamydia cases: 207.1 per 100K people (854 cases)
- Gonorrhea cases: 70.6 per 100K people (291 case)
- Syphilis cases (non-congenital): 11.6 per 100K people (48 cases)
--- Primary and secondary syphilis: 8.2 per 100K people (34 cases)
--- Nonprimary and nonsecondary early syphilis: 3.4 per 100K people (14 cases)
Matt Gush // Shutterstock
7 / 51#45. Sutter County
- Chlamydia cases: 213.0 per 100K people (211 case)
- Gonorrhea cases: 149.4 per 100K people (148 cases)
- Syphilis cases (non-congenital): 66.6 per 100K people (66 cases)
--- Primary and secondary syphilis: 41.4 per 100K people (41 case)
--- Nonprimary and nonsecondary early syphilis: 25.2 per 100K people (25 cases)
#44. San Benito County
- Chlamydia cases: 219.0 per 100K people (146 cases)
- Gonorrhea cases: 90.0 per 100K people (60 cases)
- Syphilis cases (non-congenital): 12.0 per 100K people (8 cases)
--- Primary and secondary syphilis: 9.0 per 100K people (6 cases)
--- Nonprimary and nonsecondary early syphilis: 3.0 per 100K people (2 cases)
#43. Siskiyou County
- Chlamydia cases: 224.4 per 100K people (99 cases)
- Gonorrhea cases: 99.7 per 100K people (44 cases)
- Syphilis cases (non-congenital): 45.3 per 100K people (20 cases)
--- Primary and secondary syphilis: 36.3 per 100K people (16 cases)
--- Nonprimary and nonsecondary early syphilis: 9.1 per 100K people (4 cases)
#42. Marin County
- Chlamydia cases: 229.8 per 100K people (598 cases)
- Gonorrhea cases: 81.5 per 100K people (212 cases)
- Syphilis cases (non-congenital): 16.9 per 100K people (44 cases)
--- Primary and secondary syphilis: 8.1 per 100K people (21 case)
--- Nonprimary and nonsecondary early syphilis: 8.8 per 100K people (23 cases)
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#41. Del Norte County
- Chlamydia cases: 242.0 per 100K people (68 cases)
- Gonorrhea cases: 99.6 per 100K people (28 cases)
- Syphilis cases (non-congenital): 14.2 per 100K people (4 cases)
--- Primary and secondary syphilis: 7.1 per 100K people (2 cases)
--- Nonprimary and nonsecondary early syphilis: 7.1 per 100K people (2 cases)
#40. Colusa County
- Chlamydia cases: 260.1 per 100K people (57 cases)
- Gonorrhea cases: 127.8 per 100K people (28 cases)
- Syphilis cases (non-congenital): 22.8 per 100K people (5 cases)
--- Primary and secondary syphilis: 13.7 per 100K people (3 cases)
--- Nonprimary and nonsecondary early syphilis: 9.1 per 100K people (2 cases)
Uladzik Kryhin // Shutterstock
13 / 51#39. Santa Clara County
- Chlamydia cases: 268.0 per 100K people (5,054 cases)
- Gonorrhea cases: 126.1 per 100K people (2,378 cases)
- Syphilis cases (non-congenital): 28.5 per 100K people (537 cases)
--- Primary and secondary syphilis: 15.5 per 100K people (293 cases)
--- Nonprimary and nonsecondary early syphilis: 12.9 per 100K people (244 cases)
#38. Inyo County
- Chlamydia cases: 289.9 per 100K people (55 cases)
- Gonorrhea cases: 105.4 per 100K people (20 cases)
- Syphilis cases (non-congenital): 10.5 per 100K people (2 cases)
--- Primary and secondary syphilis: 10.5 per 100K people (2 cases)
--- Nonprimary and nonsecondary early syphilis: 0 cases
#37. Shasta County
- Chlamydia cases: 289.9 per 100K people (528 cases)
- Gonorrhea cases: 208.1 per 100K people (379 cases)
- Syphilis cases (non-congenital): 53.3 per 100K people (97 cases)
--- Primary and secondary syphilis: 43.4 per 100K people (79 cases)
--- Nonprimary and nonsecondary early syphilis: 9.9 per 100K people (18 cases)
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#36. Mono County
- Chlamydia cases: 294.4 per 100K people (39 cases)
- Gonorrhea cases: 30.2 per 100K people (4 cases)
- Syphilis cases (non-congenital): 0 cases
--- Primary and secondary syphilis: 0 cases
--- Nonprimary and nonsecondary early syphilis: 0 cases
#35. Tehama County
- Chlamydia cases: 305.4 per 100K people (200 cases)
- Gonorrhea cases: 154.2 per 100K people (101 case)
- Syphilis cases (non-congenital): 61.1 per 100K people (40 cases)
--- Primary and secondary syphilis: 56.5 per 100K people (37 cases)
--- Nonprimary and nonsecondary early syphilis: 4.6 per 100K people (3 cases)
#34. Santa Barbara County
- Chlamydia cases: 317.4 per 100K people (1,417 cases)
- Gonorrhea cases: 117.4 per 100K people (524 cases)
- Syphilis cases (non-congenital): 19.3 per 100K people (86 cases)
--- Primary and secondary syphilis: 12.5 per 100K people (56 cases)
--- Nonprimary and nonsecondary early syphilis: 6.7 per 100K people (30 cases)
#33. San Mateo County
- Chlamydia cases: 317.7 per 100K people (2,344 cases)
- Gonorrhea cases: 107.2 per 100K people (791 case)
- Syphilis cases (non-congenital): 19.8 per 100K people (146 cases)
--- Primary and secondary syphilis: 8.9 per 100K people (66 cases)
--- Nonprimary and nonsecondary early syphilis: 10.8 per 100K people (80 cases)
#32. Santa Cruz County
- Chlamydia cases: 318.5 per 100K people (853 cases)
- Gonorrhea cases: 112.8 per 100K people (302 cases)
- Syphilis cases (non-congenital): 38.1 per 100K people (102 cases)
--- Primary and secondary syphilis: 24.3 per 100K people (65 cases)
--- Nonprimary and nonsecondary early syphilis: 13.8 per 100K people (37 cases)
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#31. Sonoma County
- Chlamydia cases: 332.2 per 100K people (1,614 cases)
- Gonorrhea cases: 125.3 per 100K people (609 cases)
- Syphilis cases (non-congenital): 23.9 per 100K people (116 cases)
--- Primary and secondary syphilis: 13.8 per 100K people (67 cases)
--- Nonprimary and nonsecondary early syphilis: 10.1 per 100K people (49 cases)
#30. Modoc County
- Chlamydia cases: 334.8 per 100K people (29 cases)
- Gonorrhea cases: 80.8 per 100K people (7 cases)
- Syphilis cases (non-congenital): 23.1 per 100K people (2 cases)
--- Primary and secondary syphilis: 23.1 per 100K people (2 cases)
--- Nonprimary and nonsecondary early syphilis: 0 cases
#29. San Luis Obispo County
- Chlamydia cases: 344.0 per 100K people (974 cases)
- Gonorrhea cases: 73.1 per 100K people (207 cases)
- Syphilis cases (non-congenital): 9.2 per 100K people (26 cases)
--- Primary and secondary syphilis: 7.1 per 100K people (20 cases)
--- Nonprimary and nonsecondary early syphilis: 2.1 per 100K people (6 cases)
#28. Lake County
- Chlamydia cases: 350.5 per 100K people (241 case)
- Gonorrhea cases: 248.7 per 100K people (171 case)
- Syphilis cases (non-congenital): 125.1 per 100K people (86 cases)
--- Primary and secondary syphilis: 84.3 per 100K people (58 cases)
--- Nonprimary and nonsecondary early syphilis: 40.7 per 100K people (28 cases)
#27. Humboldt County
- Chlamydia cases: 350.7 per 100K people (478 cases)
- Gonorrhea cases: 151.9 per 100K people (207 cases)
- Syphilis cases (non-congenital): 29.3 per 100K people (40 cases)
--- Primary and secondary syphilis: 19.1 per 100K people (26 cases)
--- Nonprimary and nonsecondary early syphilis: 10.3 per 100K people (14 cases)
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#26. Napa County
- Chlamydia cases: 356.8 per 100K people (486 cases)
- Gonorrhea cases: 138.8 per 100K people (189 cases)
- Syphilis cases (non-congenital): 30.8 per 100K people (42 cases)
--- Primary and secondary syphilis: 20.6 per 100K people (28 cases)
--- Nonprimary and nonsecondary early syphilis: 10.3 per 100K people (14 cases)
#25. Ventura County
- Chlamydia cases: 370.5 per 100K people (3,111 case)
- Gonorrhea cases: 110.7 per 100K people (930 cases)
- Syphilis cases (non-congenital): 24.6 per 100K people (207 cases)
--- Primary and secondary syphilis: 15.4 per 100K people (129 cases)
--- Nonprimary and nonsecondary early syphilis: 9.3 per 100K people (78 cases)
#24. Orange County
- Chlamydia cases: 373.2 per 100K people (11,822 cases)
- Gonorrhea cases: 168.6 per 100K people (5,341 case)
- Syphilis cases (non-congenital): 29.7 per 100K people (941 case)
--- Primary and secondary syphilis: 17.6 per 100K people (559 cases)
--- Nonprimary and nonsecondary early syphilis: 12.1 per 100K people (382 cases)
#23. Merced County
- Chlamydia cases: 383.6 per 100K people (1,099 cases)
- Gonorrhea cases: 170.4 per 100K people (488 cases)
- Syphilis cases (non-congenital): 33.5 per 100K people (96 cases)
--- Primary and secondary syphilis: 26.2 per 100K people (75 cases)
--- Nonprimary and nonsecondary early syphilis: 7.3 per 100K people (21 case)
#22. Yuba County
- Chlamydia cases: 399.2 per 100K people (333 cases)
- Gonorrhea cases: 215.8 per 100K people (180 cases)
- Syphilis cases (non-congenital): 79.1 per 100K people (66 cases)
--- Primary and secondary syphilis: 46.8 per 100K people (39 cases)
--- Nonprimary and nonsecondary early syphilis: 32.4 per 100K people (27 cases)
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#21. Mendocino County
- Chlamydia cases: 407.4 per 100K people (372 cases)
- Gonorrhea cases: 241.0 per 100K people (220 cases)
- Syphilis cases (non-congenital): 21.9 per 100K people (20 cases)
--- Primary and secondary syphilis: 17.5 per 100K people (16 cases)
--- Nonprimary and nonsecondary early syphilis: 4.4 per 100K people (4 cases)
#20. Yolo County
- Chlamydia cases: 409.2 per 100K people (888 cases)
- Gonorrhea cases: 161.3 per 100K people (350 cases)
- Syphilis cases (non-congenital): 25.8 per 100K people (56 cases)
--- Primary and secondary syphilis: 16.1 per 100K people (35 cases)
--- Nonprimary and nonsecondary early syphilis: 9.7 per 100K people (21 case)
#19. Contra Costa County
- Chlamydia cases: 423.9 per 100K people (4,923 cases)
- Gonorrhea cases: 179.2 per 100K people (2,081 case)
- Syphilis cases (non-congenital): 27.1 per 100K people (315 cases)
--- Primary and secondary syphilis: 16.7 per 100K people (194 cases)
--- Nonprimary and nonsecondary early syphilis: 10.4 per 100K people (121 case)
#18. Stanislaus County
- Chlamydia cases: 434.4 per 100K people (2,402 cases)
- Gonorrhea cases: 170.7 per 100K people (944 cases)
- Syphilis cases (non-congenital): 67.5 per 100K people (373 cases)
--- Primary and secondary syphilis: 46.8 per 100K people (259 cases)
--- Nonprimary and nonsecondary early syphilis: 20.6 per 100K people (114 cases)
#17. Alameda County
- Chlamydia cases: 451.8 per 100K people (7,448 cases)
- Gonorrhea cases: 231.1 per 100K people (3,809 cases)
- Syphilis cases (non-congenital): 22.7 per 100K people (375 cases)
--- Primary and secondary syphilis: 12.0 per 100K people (198 cases)
--- Nonprimary and nonsecondary early syphilis: 10.7 per 100K people (177 cases)
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#16. Imperial County
- Chlamydia cases: 470.4 per 100K people (846 cases)
- Gonorrhea cases: 137.3 per 100K people (247 cases)
- Syphilis cases (non-congenital): 18.9 per 100K people (34 cases)
--- Primary and secondary syphilis: 10.6 per 100K people (19 cases)
--- Nonprimary and nonsecondary early syphilis: 8.3 per 100K people (15 cases)
#15. Sacramento County
- Chlamydia cases: 481.1 per 100K people (7,645 cases)
- Gonorrhea cases: 277.9 per 100K people (4,416 cases)
- Syphilis cases (non-congenital): 45.3 per 100K people (719 cases)
--- Primary and secondary syphilis: 30.1 per 100K people (479 cases)
--- Nonprimary and nonsecondary early syphilis: 15.1 per 100K people (240 cases)
#14. Riverside County
- Chlamydia cases: 487.8 per 100K people (11,991 case)
- Gonorrhea cases: 200.3 per 100K people (4,924 cases)
- Syphilis cases (non-congenital): 35.4 per 100K people (871 case)
--- Primary and secondary syphilis: 16.4 per 100K people (402 cases)
--- Nonprimary and nonsecondary early syphilis: 19.1 per 100K people (469 cases)
#13. Butte County
- Chlamydia cases: 494.5 per 100K people (1,030 cases)
- Gonorrhea cases: 224.7 per 100K people (468 cases)
- Syphilis cases (non-congenital): 58.6 per 100K people (122 cases)
--- Primary and secondary syphilis: 46.6 per 100K people (97 cases)
--- Nonprimary and nonsecondary early syphilis: 12.0 per 100K people (25 cases)
#12. Monterey County
- Chlamydia cases: 503.3 per 100K people (2,201 case)
- Gonorrhea cases: 146.6 per 100K people (641 case)
- Syphilis cases (non-congenital): 17.1 per 100K people (75 cases)
--- Primary and secondary syphilis: 11.2 per 100K people (49 cases)
--- Nonprimary and nonsecondary early syphilis: 5.9 per 100K people (26 cases)
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#11. Solano County
- Chlamydia cases: 523.8 per 100K people (2,366 cases)
- Gonorrhea cases: 227.6 per 100K people (1,028 cases)
- Syphilis cases (non-congenital): 34.5 per 100K people (156 cases)
--- Primary and secondary syphilis: 22.1 per 100K people (100 cases)
--- Nonprimary and nonsecondary early syphilis: 12.4 per 100K people (56 cases)
#10. San Joaquin County
- Chlamydia cases: 535.5 per 100K people (4,227 cases)
- Gonorrhea cases: 222.2 per 100K people (1,754 cases)
- Syphilis cases (non-congenital): 45.4 per 100K people (358 cases)
--- Primary and secondary syphilis: 24.7 per 100K people (195 cases)
--- Nonprimary and nonsecondary early syphilis: 20.6 per 100K people (163 cases)
#9. Madera County
- Chlamydia cases: 543.9 per 100K people (867 cases)
- Gonorrhea cases: 141.1 per 100K people (225 cases)
- Syphilis cases (non-congenital): 27.6 per 100K people (44 cases)
--- Primary and secondary syphilis: 22.6 per 100K people (36 cases)
--- Nonprimary and nonsecondary early syphilis: 5.0 per 100K people (8 cases)
#8. San Diego County
- Chlamydia cases: 552.0 per 100K people (18,138 cases)
- Gonorrhea cases: 247.9 per 100K people (8,147 cases)
- Syphilis cases (non-congenital): 38.3 per 100K people (1,259 cases)
--- Primary and secondary syphilis: 18.8 per 100K people (617 cases)
--- Nonprimary and nonsecondary early syphilis: 19.5 per 100K people (642 cases)
#7. San Bernardino County
- Chlamydia cases: 579.5 per 100K people (12,719 cases)
- Gonorrhea cases: 253.0 per 100K people (5,552 cases)
- Syphilis cases (non-congenital): 40.1 per 100K people (881 case)
--- Primary and secondary syphilis: 21.1 per 100K people (462 cases)
--- Nonprimary and nonsecondary early syphilis: 19.1 per 100K people (419 cases)
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#6. Los Angeles County
- Chlamydia cases: 580.4 per 100K people (57,048 cases)
- Gonorrhea cases: 316.4 per 100K people (31,097 cases)
- Syphilis cases (non-congenital): 63.4 per 100K people (6,231 case)
--- Primary and secondary syphilis: 27.3 per 100K people (2,686 cases)
--- Nonprimary and nonsecondary early syphilis: 36.1 per 100K people (3,545 cases)
#5. Tulare County
- Chlamydia cases: 611.9 per 100K people (2,919 cases)
- Gonorrhea cases: 170.2 per 100K people (812 cases)
- Syphilis cases (non-congenital): 37.9 per 100K people (181 case)
--- Primary and secondary syphilis: 27.7 per 100K people (132 cases)
--- Nonprimary and nonsecondary early syphilis: 10.3 per 100K people (49 cases)
#4. Fresno County
- Chlamydia cases: 637.3 per 100K people (6,460 cases)
- Gonorrhea cases: 266.8 per 100K people (2,704 cases)
- Syphilis cases (non-congenital): 44.2 per 100K people (448 cases)
--- Primary and secondary syphilis: 25.4 per 100K people (257 cases)
--- Nonprimary and nonsecondary early syphilis: 18.8 per 100K people (191 case)
#3. Kern County
- Chlamydia cases: 650.7 per 100K people (5,971 case)
- Gonorrhea cases: 243.1 per 100K people (2,231 case)
- Syphilis cases (non-congenital): 59.4 per 100K people (545 cases)
--- Primary and secondary syphilis: 30.9 per 100K people (284 cases)
--- Nonprimary and nonsecondary early syphilis: 28.4 per 100K people (261 case)
#2. Kings County
- Chlamydia cases: 671.3 per 100K people (1,030 cases)
- Gonorrhea cases: 210.5 per 100K people (323 cases)
- Syphilis cases (non-congenital): 20.9 per 100K people (32 cases)
--- Primary and secondary syphilis: 16.3 per 100K people (25 cases)
--- Nonprimary and nonsecondary early syphilis: 4.6 per 100K people (7 cases)
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#1. San Francisco County
- Chlamydia cases: 791.2 per 100K people (6,450 cases)
- Gonorrhea cases: 674.3 per 100K people (5,497 cases)
- Syphilis cases (non-congenital): 151.7 per 100K people (1,237 cases)
--- Primary and secondary syphilis: 50.2 per 100K people (409 cases)
--- Nonprimary and nonsecondary early syphilis: 101.6 per 100K people (828 cases)
This story features data reporting and writing by Emma Rubin and is part of a series utilizing data automation across 49 states.
