Sexually transmitted infection screening (Family medicine): Clinical sciences

Sexually transmitted infections, also known as STIs, are infections acquired through sexual contact. While many STIs have symptoms, some patients present asymptomatically. For this reason, screening is important in diagnosing and treating STIs. Screening also provides an opportunity to educate patients on safe sexual practices and disease prevention. Specific screening recommendations for STIs vary according to biological sex, pregnancy status, sexual preference, and HIV status.

For patients presenting for STI screening, first perform a focused history and physical examination.

The patient might be asymptomatic, or they may report STI symptoms, such as dysuria, genital discharge, or rash. There also might be a history of known STI exposure. If so, ask about the timing of the sexual exposure and review previous screenings or treatment results. Physical examination may show cervical or penile discharge, or possibly genital, rectal, or pharyngeal lesions.

Here’s a clinical pearl! Patients who are high-risk for STIs include those who have multiple sex partners, engage in transactional sex, use illicit substances, or have a history of incarceration.

Here’s another clinical pearl! STI screening can be completed at a specific STI screening visit or as part of a preventative visit, like a well-patient care exam. STI screening can also be completed without a physical exam by patient-collected swabs, and lab tests such as blood and urine tests; however, this type of screening is only appropriate for asymptomatic patients.

Okay, let’s start by talking about which infections are screened for and how that screening is completed.

Chlamydia, caused by Chlamydia trachomatis, is the most frequently reported bacterial STI with the highest prevalence in patients who are under 25 years of age. Gonorrhea, caused by Neisseria gonorrhoeae, is the second most frequently reported bacterial STI. Testing for both is completed through a nucleic acid amplification test or NAAT.

If a provider obtains a sample for testing, a specimen collection swab is used to obtain the sample from the patient’s cervix or urethra. If the patient collects their own sample, either a vaginal swab or first catch urine specimen can be used. Positive results are reported to the CDC.

On the other hand, trichomoniasis, caused by Trichomonas vaginalis, is not a reportable disease. That said, it has a higher prevalence rate than gonorrhea or chlamydia and is known to increase the risk of HIV. Testing is done by NAAT test using a cervical or vaginal swab, or a first catch urine sample.

NAAT is preferred for its increased specificity and sensitivity, but screening can also be completed via wet mount microscopy with visualization of motile trichomonads, which confirms the diagnosis.

HIV screening is typically completed by using an antigen/antibody test for HIV 1 and 2. Positive test results are reportable to the CDC.

Next, syphilis screening, which is caused by Treponema pallidum, is usually completed by a two-step process. A non-treponemal test is obtained first, either a Venereal Disease Research Laboratory, or VDRL; or Rapid Plasma Reagin, or RPR. This is followed by a treponemal test, such as the T. pallidum passive particle agglutination, or TP-PA test. A positive test is reportable to the CDC. Remember to test these patients for HIV too since there is a possibility of co-infection.

Now, hepatitis B screening has traditionally been done by checking for hepatitis B surface antigen or HBsAg. However, the CDC now recommends the triple panel test. This panel is composed of HBsAg; antibody to hepatitis B surface antigen, or anti-HBs; and total antibody to hepatitis B core antigen, or total anti-HBc. This test is recommended because there can be a window during an acute infection when the HBsAg and anti-HB are both negative. During this window, the only test that can accurately detect an acute infection is the total anti-HBc. Positive results are reported to the CDC.

Moving on, hepatitis C screening is simple and is done by checking for serum hepatitis C antibodies. Positive results are reported to the CDC.

Now, screening for human papillomavirus, or HPV, looks for high-risk types of the human papilloma virus, and is usually co-tested along with routine cervical cancer screenings, as indicated based on age and previous screening.

Finally, herpes simplex virus screening, or HSV, is only indicated when a patient has a suspicious genital lesion. These lesions are initially painful and vesicular and are followed by ulceration. A prodromal period of tingling or itching may precede their appearance. HSV testing is done by obtaining a swab of fluid from the ulcer, which is analyzed by polymerase chain reaction, or PCR for both HSV 1 and 2. Keep in mind that testing is not always necessary, and the diagnosis can be made clinically.

While traditionally HSV 1 was thought to only cause oral herpes or cold sores and HSV 2 only caused genital outbreaks, evidence shows that either strain of the virus can cause an outbreak in either area. Additionally, all patients who have suspicious lesions should also have serology testing for type-specific antibodies to HSV 1 and 2.

Now, let's break down screening recommendations into patient categories, by assessing your patient’s biological sex. Keep in mind that for transgender and gender-diverse patients, you should screen for STIs according to their anatomy.

If your patient is a biological female, assess their pregnancy and HIV status. Let’s start with non-pregnant biological females without HIV. Screen these patients for chlamydia and gonorrhea for sexually active patients under 25 years old.

HIV screening is recommended for patients aged 13 to 64 years of age as an opt-out modality, meaning they will be tested for HIV unless they specifically decline the screening.

Hepatitis C screening is recommended for those over the age of 18, except in settings where the hepatitis C positivity is less than 0.1 percent.

Now, human papillomavirus screening, or HPV, looks for high-risk types of the human papilloma virus, and can be co-tested along with routine cervical cancer screenings, as indicated based on age and previous screening.