What is a sexually transmitted disease, or STD? If someone catches their partner’s cold during sex, is that cold an STD? According to the Office on Women’s Health, an STD is “an infection passed from one person to another person through sexual contact.” Unless the cold was passed through sexual contact, rather than mouth-to-mouth contact, it would not be considered an STD. Others say that, for an infection to be considered an STD, its sexual transmission must make it significantly more common in the population. So, a disease like the common cold would probably be just as common even if people never had sex.

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MRSA, meningitis, and the virus that causes pinkeye can be transmitted sexually.

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However, there are some infections, such as hepatitis C or bacterial vaginosis, whose status as official STDs is controversial. While researchers argue with one another over where to draw the line between an STD and a non-STD, let’s take a look at some bacteria and viruses that can be transmitted sexually, even though they’re not officially categorized as “STDs.”

MRSA: Methicillin-Resistant Staphylococcus aureus

MRSA bursting out of a dead blood cell. Image: Frank DeLeo, NIAID

You’ve probably heard of MRSA, which is pronounced “mersa” and stands for methicillin-resistant Staphylococcus aureus — a strain of bacteria that is resistant to every antibiotic in the penicillin family, as well as others. S. aureus, or “staph” for short, is the same bacteria responsible for TSS, or toxic shock syndrome, which has most infamously been associated with the use of highly absorbent tampons. But mostly, staph is a common cause of skin infections, which could be deadly in the pre-antibiotic era, but these days usually don’t raise too many eyebrows.

Unfortunately, with the emergence of MRSA, which is difficult to treat with the usual drugs, we might once again have to worry about minor skin infections blossoming into life-threatening conditions. Additionally, MRSA has found a way to hop from person to person via sexual contact, and sexually transmitted MRSA has been documented in both heterosexual and MSM (men who have sex with men) populations. Untreated, it can lead to a form of gangrene in which tissue blackens as it dies.

It’s possible that MRSA can be present in the vagina or rectum, and transmitted by vaginal or anal sex. But most researchers think it’s spread by intimate skin-to-skin contact — and skin injuries might make one even more vulnerable. The evidence is thin, but shaving might increase MRSA risk by causing small cuts that leave the skin vulnerable to infection. Other researchers point to poor skin care, including the use of skin-drying lubricants, as leading to dry skin, which can increase infection risk. However, it’s also possible for MRSA to be transmitted by shared sheets or towels, leading some researchers to cast doubt on the sexual transmission of MRSA. Other researchers point out that MRSA is rare in the vagina, and that if it were sexually transmitted, we might expect to see more vaginal MRSA than we do.

Sexually transmitted MRSA has been studied more extensively in the MSM population, in whom it can cause skin infections of the buttocks, genitals, and perineum. MSM are more likely to catch sexually transmitted MRSA if they have any of the following risk factors:

• multiple partners or group sex
• skin-abrading sexual activities
• use of Internet hookup apps
• a previous history of STDs
• methamphetamine (“meth”) use, which can cause users to pick at their skin

Because genital MRSA infections can look so much like herpes, syphilis, and lymphogranuloma venereum (LGV), health-care providers need to be aware that MRSA is another possible culprit behind ulcers and abscesses in the genital region.

Meningitis: Usually an Above-the-Belt Infection

Neisseria meningitidis

Urethritis is an inflammation of the urethra, characterized by discharge and a burning sensation while urinating. When urethritis is caused by bacteria called Neisseria gonorrhoeae, the infection is called gonorrhea. Otherwise, it’s called nongonococcal urethritis, or NGU. While Chlamydia trachomatis, the bacteria that causes chlamydia, is responsible for up to 40 percent of NGU cases, other germs can cause it as well.

Last summer, the Centers for Disease Control and Prevention released a report detailing an increase in NGU cases caused by Neisseria meningitidis, a close relative of the bug behind gonorrhea, but which causes meningitis, an inflammation of the protective membranes covering the brain and spine. College students living in dorms are often required to receive the meningitis vaccine, as meningitis spreads through close contact and outbreaks have occurred on college campuses. It can also be transmitted by kissing — but, just as the bug that causes it can travel from one mouth to another, so too can it travel from a mouth to a penis during oral sex.

Luckily, urethritis caused by N. meningitis is treated with the same drugs used for gonorrhea — meaning that a doctor can mistake meningococcal NGU for gonorrhea and still prescribe the correct antibiotics.

Adenovirus: The Virus that Causes Pinkeye

Adenovirus. Image: Dr. G. William Gary, Jr., CDC

Adenoviruses are a class of viruses most famous for causing the common cold, bronchitis, and pinkeye. It’s usually spread by touching; coughing or sneezing; or touching your mouth, nose, or eyes after touching contaminated objects. However, certain strains of adenovirus can also cause NGU. Yep, you can give pinkeye to a penis.

Researchers have demonstrated that receiving oral sex increases urethritis risk for someone with a penis, as saliva and other oral secretions contain high viral concentrations. Symptoms can include painful urination and the inflammation of the tip of the penis — and sufferers frequently have pinkeye as well. Symptoms last for an average of two weeks, though one study reported that symptoms resolved in one week. There’s also some evidence that sexually transmitted adenovirus could be seasonal, with cases spiking in the autumn.

It seems logical to assume that adenovirus is passed directly from the mouth of an infected “giver” of oral sex to an uninfected “receiver” of oral sex, but it’s also possible that, since adenoviruses can live in the rectum or female reproductive tract, it infects a penis via unprotected anal or vaginal sex. Or perhaps someone can be infected with adenovirus through nonsexual transmission, and the virus invades the body, wending its way to the genital tract. Of course, other types of intimate activities, like kissing, can allow people to swap spit (and viruses). And, when someone has pinkeye, it’s possible that he can infect himself by touching his eye and then touching his penis — no sexual contact required.

Unlike gonorrhea, chlamydia, and other bacterial diseases, adenovirus infections cannot be cured with antibiotics — so if a doctor assumes symptoms are caused by bacteria, a course of antibiotics will be useless. While there isn’t a cure for adenoviral urethritis, the good news is that, just like pinkeye, it goes away after a while, defeated by the body’s own immune system. You can prevent the transmission of adenovirus by washing your hands, not sharing towels, and avoiding sexual contact until your symptoms are gone.

The best way for sexually active people to avoid STDs is to use condoms and dental dams consistently and correctly, be screened for STDs before initiating sexual activity, and limit sexual partners. Planned Parenthood health centers can diagnose and treat STDs.

Click here to check out other installments of our monthly STD Awareness series!