What STIs are "testable" and who is infected, anyway?

Dear Trying to make a more informed decision,

You’re doing an excellent job of looking out for your health and being a responsible sexual partner. Many people have run up against the frustration of fuzzy answers regarding sexually transmitted infections (STIs), testing, and safer sex. Unfortunately, there isn't an all-in-one test for all STIs, and not all STIs are tested for routinely, as you've discovered. And while being aware of the STI rates in the general population may be one piece of information to inform your sexual decision making, often health care providers make recommendations based on an individual level with a combination of different types of information, including a person's sexual history, any reported symptoms, and testing guidelines. When it comes to prevention though, you’re off to a great start by speaking with your partner about sexual histories, contraceptive options, and STI testing. Limiting your number of partners, using condoms and other barrier methods, and getting tested for STIs with new sexual partners will also help you reduce your risk. But in the end, sex (of any kind) involves some amount of risk, so when determining how to move forward and whether to continue using condoms, it's wise to figure out how much risk you and your partner are comfortable with together.

You asked about the number of infections among the general public. The Centers for Disease Control and Prevention (CDC) estimates that there are 20 million new STIs that occur every year in the U.S. — half of which are diagnosed in young people ages 15 to 24. Beyond that estimate, prevalence rates (how many people have an infection) vary for each STI and among different groups of people. There are a few reasons for the differences:

• If a person doesn't experience typical symptoms (which can be the case with a number of STIs, including chlamydia and herpes), they may not get tested. This means that some positive cases aren't being diagnosed and, in turn, prevalence rates for certain STIs that are commonly asymptomatic don’t truly represent the total number of people who have the infection.
• There are different reporting requirements for various STIs. For example, chlamydia, gonorrhea, and syphilis are reportable diseases. This means that positive diagnoses for these STIs must be shared with the CDC. This allows for more systematic tracking of the infections and it helps in form prevention efforts on a larger scale. In contrast, though, infections such as herpes, trichomoniasis, and human papillomavirus (HPV) are not reported routinely, making those positive diagnoses more difficult to track and quantify.
• Some groups of people within the general population are at higher risk for STIs than others. For example, due to a number of behavioral, cultural, and social factors, men who have sex with men (MSM) typically have higher rates of some STIs than the general population. Because of this, looking at the STI rates among a specific subgroup of the general population (which may be segmented by age, sexual orientation, ethnicity, gender, socioeconomic status, etc.) may sometimes provide more nuanced insights about STI rates.  

With that said, prevalence rates are available (to some degree) for the general public for many STIs and can provide some information to help you decide how to protect yourself. Being aware of STI testing and testing recommendations, as you indicated, is another set of useful information. Here are a few details on number of common STIs, how prevalent they are, and testing information:

Trichomoniasis: This is the most common non-viral infection in the U.S., with about 3.7 million people infected. Of that number, only about 30 percent will actually develop symptoms. The infection is more common in women and in older people. If symptoms are present, diagnosis is made through visual examination and a laboratory test of vaginal or urethral discharge to confirm an infection.

Human papillomavirus (HPV): There are over 100 strains of HPV, and about 40 tend to affect the genital area; some strains cause genital warts and some are associated with cancers of the cervix, penis, vagina, and throat. HPV is the most common STI in the U.S. — most sexually active people will acquire it at some point in their lives. Diagnosis of low-risk (non-cancerous) HPV is typically associated with the visual confirmation of genital warts in males or females. Though high-risk HPV strains may cause transient infections (ones that go way over time on their own), other strains may persist. Testing for high-risk HPV in women is done with a Pap test (there is no high-risk HPV test for men). If a Pap test has an abnormal result, it will typically be followed up with a colposcopy and potentially a HPV test. 

Herpes: About 50 million people in the U.S. has genital herpes. Like HPV, herpes is difficult to diagnose without visible sores, and many people have no symptoms. The infection is slightly more common in women than men. A blood test and fluid test are available to detect the herpes virus, but the results aren't always conclusive. That being the case, it's not usually done unless a person presents with typical symptoms or suspects exposure to the virus (thus, it’s not routine).

Chlamydia: In 2014, 1.4 million cases of chlamydia were reported to the CDC, but it’s estimated that almost three million cases occur annually in the United States. Chlamydia infections are under-reported because most people do not experience symptoms. No matter if symptoms are present or not, chlamydia may be diagnosed using a urine sample or a swab test of the penis, vagina, cervix, anus, or throat.

Human immunodeficiency virus (HIV): The CDC estimates that about 1.2 million people over the age of 13 in the U.S. are living with HIV, and almost 12.8 percent are unaware of their infection. Again, it’s good to point out that prevalence numbers for this specific infection vary among specific populations when segmented by ethnicity, sexual behaviors, geographic area, and age. HIV testing can easily be done with a blood test or an oral swab.

Hepatitis B: There are between 700,000 and 1.4 million people in the U.S. with chronic Hepatitis B. This viral STI is diagnosed with a blood test, but health care providers typically will not routinely test you for it you aren’t at high-risk for the infection.

Gonorrhea: In 2014, there were approximately 350,000 cases of gonorrhea in the U.S., with the highest rates among sexually active teenagers, young adults, and African Americans. Similar to chlamydia, this bacterial infection may be asymptomatic. Testing for gonorrhea and chlamydia are most often done simultaneously, with either a urine test (most common), through a sample of discharge (if present), or a swab test of the penis, vagina, anus, or throat.  

Syphilis: In 2014, about 20,000 new cases of syphilis were reported in the U.S. Some health care providers can diagnose syphilis by examining a sample from sores using a special microscope called a dark-field microscope. If syphilis bacteria are present in the sore, they will show up when observed through the microscope. Another way to test for syphilis is through a blood test.

Because this isn’t an exhaustive list, your best bet is to consult a health care provider to round out your fact-finding investigation. They can help you determine your individual risk and what makes sense for you in terms of STI testing and prevention.

Lastly — to use a condom or not to use a condom — that is your other question. If only the answer were so simple. As you probably realize, the only way to avoid the risk of STIs is to avoid sexual contact, including oral, vaginal, and anal sex. That being said, many people weigh the pros and cons and accept some level of risk when they decide to be sexually active. At that point, communication and cooperation between you, your partner(s), and your health care provider becomes essential for reducing your risk as much as possible. For even more advice as you consider continued condom use, check out Monogamous couple: Stop using condoms? in the Go Ask Alice! archives.