Colorado ranks among the states with the lowest rates when it comes to several common sexually transmitted diseases, as the state’s rates of several STDs, including chlamydia, gonorrhea and syphilis are lower than the overall national rates. However, the news is not all good in our state, as most STDs have seen their prevalence in Colorado rise in recent years, which largely tracks with a national trend in which STD rates have climbed for four straight years.

So which STDs are most common in Colorado, how have rates of some of the most common STDs changed here over time, and how do rates vary depending on the state’s geography? To understand the picture of sexually transmitted diseases and infections in Colorado, let’s examine data from the federal Centers for Disease Control and Prevention as well as the Colorado Department of Public Health & Environment.

Chlamydia Rates in Colorado

More than 26,000 people were diagnosed with chlamydia in Colorado in 2017, putting the state right in the middle when it comes to overall cases. But after adjusting for population size, Colorado drops a few places to No. 30 among the 50 states. Colorado’s chlamydia rate is about 8% lower than the overall U.S. rate.

Chlamydia infections per 100,000 people, bottom 25

Connecticut 496.3
Virginia 488.3
Florida 485.2
Wisconsin 485
Colorado 481.3
Hawaii 479.5
Kansas 466.2
Oregon 455.2
Nebraska 450.7
Minnesota 444
Iowa 443.2
Washington 442.2
Pennsylvania 441.5
Montana 437.4
Kentucky 435.4
North Dakota 432.5
Massachusetts 425.7
New Jersey 392
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

While the state’s overall ranking among all states is relatively positive, chlamydia has climbed sharply in Colorado in recent years, jumping nearly 25% since 2008.

Colorado chlamydia rate by year (cases per 100,000 people)

2008 391.3
2009 402
2010 385.1
2011 426.1
2012 416.8
2013 387.1
2014 409
2015 438.2
2016 462.1
2017 481.3

Two Western states, Alaska and New Mexico, are among the top five nationally, but Colorado still ranks in the top half of the region.

Chlamydia infection rate, Western states (cases per 100,000 people)

Alaska 799.8
New Mexico 651.6
Arizona 571.8
California 557.4
Nevada 553.1
Colorado 481.3
Hawaii 479.5
Oregon 455.2
Washington 442.2
Montana 437.4
Idaho 368.4
Wyoming 365.8
Utah 332.2

 Gonorrhea Rates in Colorado

Colorado just barely ranks in the bottom half of all states when it comes to the prevalence of gonorrhea in our state. Colorado’s population-adjusted gonorrhea rate is about 12% lower than the overall national rate.

Gonorrhea infections per 100,000 people

Florida 153.7
Colorado 151.1
South Dakota 149.1
Virginia 143.3
Minnesota 142
Nebraska 139.1
Washington 136
Wisconsin 135
North Dakota 127.4
Oregon 122.7
Iowa 119.9
Pennsylvania 119.2
Connecticut 109.4
Massachusetts 106.5
New Jersey 105.5
Rhode Island 102.9
Hawaii 95.1
Utah 83.3
Montana 75
West Virginia 70.8
Wyoming 70.4
Idaho 58.6
Maine 46.6
New Hampshire 38.4
Vermont 32.5
Total 171.9

Colorado has seen a huge explosion in the gonorrhea rate with a one-year increase of nearly 40% between 2016 and 2017 and a 97% increase over the past 10 years.

Colorado gonorrhea rate by year (cases per 100,000 people)

2008 76.6
2009 56.7
2010 55.2
2011 46.2
2012 54.4
2013 53.5
2014 59.3
2015 80.6
2016 108
2017 151.1

Colorado ranks in the top half regionally when it comes to the prevalence of gonorrhea, though the state’s rate is just over half that of Alaska, the regional leader and No. 2 state overall.

Gonorrhea infection rate, Western states (cases per 100,000 people)

Alaska 295.1
New Mexico 215.7
California 192
Nevada 187.8
Arizona 180.5
Colorado 151.1
Washington 136
Oregon 122.7
Hawaii 95.1
Utah 83.3
Montana 75
Wyoming 70.4
Idaho 58.6

Syphilis Rates in Colorado

Colorado comes in 33rd overall nationally in the population-adjusted rate of infections of primary and secondary syphilis, and the state’s rate is just over half the overall U.S. rate.

Primary and secondary syphilis infections per 100,000 people, bottom 25

Pennsylvania 6.2
Virginia 6
Delaware 6
Kentucky 5.9
North Dakota 5.8
New Jersey 5.6
Minnesota 5.5
Colorado 5.2
Maine 4.9
Michigan 4.8
Indiana 4.8
Kansas 4.6
Montana 4.6
South Dakota 3.8
Utah 3.8
Idaho 3.8
West Virginia 3.4
Iowa 3.2
New Hampshire 3.2
Connecticut 3.1
Wisconsin 3
Nebraska 2.3
Vermont 2.1
Alaska 1.8
Wyoming 0.7
Total 9.5

Syphilis has made a roaring comeback in the state after rates dipped into the low single digits. Since 2008, the infection rate of primary and secondary syphilis has doubled in Colorado.

Colorado primary and secondary syphilis rate by year (cases per 100,000 people)

2008 2.6
2009 2.1
2010 2.7
2011 2.6
2012 4
2013 3.1
2014 3.5
2015 4.5
2016 4.5
2017 5.2

Colorado’s syphilis rate places the state in the bottom half among regional neighbors, far behind regional and overall national leader, Nevada.

Primary and secondary syphilis infection rates, Western states (cases per 100,000 people)

Nevada 20
California 17.1
Arizona 13.1
Washington 9.3
New Mexico 9.3
Oregon 8.6
Hawaii 6.6
Colorado 5.2
Montana 4.6
Utah 3.8
Idaho 3.8
Alaska 1.8
Wyoming 0.7

HIV & Other STD Rates in Colorado


Nearly 450 people were newly diagnosed with HIV in Colorado in 2017, and the state is 24th overall in population-adjusted HIV rates. But Colorado is one of only 18 states to see an increase in the prevalence of HIV between 2016 and 2017, though the increase (3%) was slight. See Best Ways to Test for HIV

Hepatitis B & C

Acute infections of both hepatitis B and hepatitis C are less common in Colorado than in the United States overall. Acute hep C cases occur at a rate about 40% lower in Colorado than in the rest of the country, and hep C infections have dropped slightly in recent years. Hep B occurs at about half the national rate in Colorado, and the rate has remained steady over the past five years. See Best Ways to Test for Hepatitis C


Colorado has the sixth-lowest rate of cancers related to human papillomavirus, which, in addition to being the most common STD in the world, is also the primary cause of several types of cancer, most famously cervical cancer. HPV-related cancers occur in Colorado at a rate of 10.3 per 100,000, compared to the national median of 11.7 per 100,000. Pinpointing exactly how many people in Colorado have HPV at any given time is difficult because the virus rarely causes symptoms, but untreated HPV can be devastating, including leading to cervical and other cancers, such as penile and anal cancer. See Best Ways to Test for HPV

STDs in Colorado Cities & Counties

While the state generally ranks relatively low nationally, several locales in Colorado have much higher rates of STDs than the state of Colorado, particularly the city of Denver.


Denver accounted for about 1 in 4 chlamydia cases in Colorado in 2017.

Colorado counties by chlamydia infection rate (cases per 100,000 people), top 10

Denver 981.5
Alamosa 604.1
Arapahoe 578.0
Pueblo 571.8
Adams 562.6
El Paso 534.5
Rio Grande 533.3
Prowers 524.8
Huerfano 514.8
Montezuma 510.1


More than a third of all gonorrhea cases were diagnosed among those living in Denver in 2017.

Colorado counties by gonorrhea infection rate (cases per 100,000 people), top 10

Denver 399.6
Alamosa 286.5
Pueblo 284.4
Montezuma 230.1
Arapahoe 187.6
Crowley 173.8
Adams 160.4
Weld 158
El Paso 152.9
Otero 141.5

Primary and secondary syphilis

Nearly half of all infections of primary and secondary syphilis in Colorado in 2017 were among those living in Denver.

Colorado counties by primary and secondary syphilis infection rate (cases per 100,000 people)

Denver 18.8
Rio Grande 8.9
Fremont 8.4
Prowers 8.3
Archuleta 7.5
La Plata 7.2
Adams 6.8
Pueblo 5.4
Mesa 5.3
Arapahoe 4.5


Colorado isn’t among the states with the highest rates of some of the most common sexually transmitted infections, but that’s no reason for complacency if you live in Colorado. That’s because rates of most sexually transmitted infections and diseases are going up in our state, and most people who are infected aren’t aware of it, which is why it’s so easy to pass STDs along to sexual partners. The best way to be sure you aren’t doing that is to get tested so you can find out what your STD status is.

Additional References

Note: Some states have published more recent data for chlamydia, gonorrhea, and primary and secondary syphilis. For states in which that’s the case, we have substituted the individual state data for 2018 and used that in our rankings, while other states’ rankings are based on 2017 numbers. In some cases, we assume that when the full national dataset is published by the CDC, states’ positions relative to other states will change some, though those changes are unlikely to be dramatic, since the CDC data comes from the states.


by AtHomeSTDKit

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