Causes of STIs When No One Has Cheated

Despite what you may think, it is possible to get a sexually transmitted infection (STI) like chlamydia, gonorrhea, or herpes without your partner cheating on you. This could be due to a long-standing infection that was never diagnosed or one that is asymptomatic (symptom-free). It is also possible for an STI treatment to fail, erasing the symptoms but not the underlying infection.

When dealing with an STI, the first and most important thing to do is get treated. It is also important to know the source of the infection so that that person can get treated, too.

This article describes five scenarios in which a partner could have an STI even though there was no infidelity in the relationship.

Preexisting Infections

One possible reason for an unexplained STI is that your partner got an STI before the two of you entered into a relationship.

The simple fact is that many STIs do not manifest with symptoms right away. Usually, there is an incubation period, meaning the time between exposure to the STI and the appearance of symptoms.

With some STIs like genital herpes, human papillomavirus (HPV), and HIV, symptoms may not appear for months or even years. At the same time, many chlamydia or gonorrhea infections are subclinical (meaning that they don't produce notable symptoms) or produce generalized, non-specific symptoms that are easily mistaken for other conditions like a urinary tract infection.

Treatment Failure

If your partner gives you an STI, it may be because an old infection wasn't fully cleared when it was first treated. One prime example of this is syphilis, a common STI that occurs in four distinct stages, referred to as primary, secondary, latent, and tertiary syphilis.

If treatment fails at any of the stages, the disease can progress invisibly and may only become apparent weeks, months, or years later when severe symptoms develop—or a sexual partner is infected.

With syphilis, the failure often occurs in one of two ways:

• Primary failure: Primary syphilis is cured with a single injection of penicillin G, which usually clears the infection but not always. During this time, a person may assume the infection has cleared because the syphilis sore (chancre) is gone. But the simple fact is that the sore is self-limiting and will vanish whether treatment is given or not.
• Secondary failure: If primary syphilis advances to secondary syphilis, the infection will be more difficult to treat and three times more likely to fail. If it fails, you may not even realize it because the infection will soon enter the latent stage where there may be no symptoms for 20 years (until the most severe stage called tertiary syphilis develops).

Treatment can also fail because of antibiotic resistance. This is common with bacterial STIs like chlamydia. If you do not take the full course of antibiotics as prescribed (or stop early), you can become resistant, making the infection harder to treat if you get it again.

Incomplete STI Screening

There are more than 20 different STIs caused by bacteria, viruses, and parasites, each of which is diagnosed in a different way. Some are diagnosed with blood or urine tests, while others involve swabs of genital, anal, or oral sores or secretions.

If you are screened for STIs, your healthcare provider is not likely to test for every infection out there and is more likely to limit the testing to common STIs like chlamydia, gonorrhea, syphilis, and HIV. Other less common STI test may only be ordered if you belong to certain high-risk groups.

At the same time, the healthcare provider may only perform a swab test on your genitals—such as for gonorrhea, chlamydia, herpes, and HPV—and not think of testing the mouth, throat, or anus. In such cases, an STI may go undiagnosed until the infection is passed to someone else.

False-Negative Tests

False-negative results are those in which you have an STI even if the test says that you don't. This can occur with antibody tests that detect immune proteins, called antibodies, that are produced in response to the infection.

During the incubation period, it can take time for the body to produce enough antibodies to reach detectable levels in blood tests. If you test during this so-called "window period," you may get a false-negative result and end up passing the infection to your partner.

This is why STI clinics will routinely ask when you think you were exposed. In some cases, they may ask you to come back simply because you are testing too early to attain an accurate result.

Asymptomatic Infections

People infected with chlamydia, gonorrhea, herpes, HIV, and HPV are often asymptomatic but still can infect others without even realizing they have an STI.

This is especially true with herpes, an incurable infection in which the vast majority of people are asymptomatic—and will never have symptoms.

The herpes virus is most often latent (dormant) but can suddenly activate during episodic flare-ups. This is true whether a person has symptoms or not. During asymptomatic flares, a person will shed viruses through the skin and can infect others without even knowing it.

Similarly, up to 75% of females with chlamydia are asymptomatic.

Ways STIs Are Not Transmitted 

Generally speaking, STIs are transmitted by close intimate contact and cannot be passed by:

• Toilet seats
• Hugging
• Handshaking
• Non-sexual kissing
• Mosquitos
• Shared utensils
• Toothbrushes
• Dental procedures

But there are exceptions.

It is sometimes possible to pass an STI via fomite transmission (objects or materials). This happens when body fluids from someone with an STI get on surfaces and objects. If you come into contact with these fluids, it is possible to get infected due to hand-to-mouth or hand-to-genital contact.

Only certain STIs are readily passed by fomite transmission, The three most likely are HPV, hepatitis B, and hepatitis C. Other STIs are more difficult to pass this pass this way.

Summary

If you're in a monogamous relationship and either you or your partner develops an STI, keep in mind that the infection may not indicate that your partner was unfaithful. An STI screen may provide answers about who infected whom and when the initial infection took place.

A Word From Verywell

A positive STI test doesn't necessarily mean your partner has been unfaithful, but it can be hard to tell when you were exposed and from whom. It's a good idea to get regular STI testing if you are sexually active, which can help narrow down the timeline of exposure. Testing is recommended before every new monogamous relationship or every few months if active with more than one partner.

— CORDELIA NWANKWO, MD, MEDICAL EXPERT BOARD