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Sexually transmitted infections: Clinical practice

Sexually transmitted infections: Clinical practice


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USMLE® Step 2 style questions USMLE

51 questions

A 22-year-old nulligravida woman presents to the walk-in clinic with abnormal vaginal odor. The vaginal odor started two weeks ago and has not improved. She has also noticed vaginal discharge, but denies vaginal bleeding, nausea, vomiting, fever, chills, and abdominal pain. She explains her menstrual period comes every 28 days and the flow is regular. The patient notes she is sexually active with two men and has not been using condoms regularly. Examination shows that her temperature is 37℃ (98.6℉), blood pressure is 125/85 mm Hg, pulse is 85/min, and respirations are 15/min. Pelvic examination reveals thin and frothy vaginal discharge and a normal-appearing cervix. Which of the following is the most appropriate next step in management? 


Content Reviewers:

Rishi Desai, MD, MPH

Sexually transmitted infections or STIs are infections that get transmitted through sexual fluids or skin-to-skin contact during sexual intercourse. Some STIs primarily affect the genital organs- like gonorrhea and chlamydia, while others affect the whole body- like syphilis, HIV, and hepatitis B. Generally, with STIs, all partners with whom there has been sexual contact in the 60 days prior to the diagnosis should be evaluated and treated. On a side note, in this video we’ll be using the term “female” to refer to individuals who have female reproductive sex organs, and the term “male” to refer to those who have male reproductive sex organs.

Okay, let’s start with infections that mainly affect the genital organs like Neisseria gonorrhoeae- which causes gonorrhea, Chlamydia trachomatis which causes chlamydia, and Mycoplasma genitalium - an increasingly recognized pathogen. These infections are usually asymptomatic, but in females, they can cause cervicitis and urethritis. Cervicitis causes changes in vaginal discharge, pruritus in the genital area, intermenstrual vaginal bleeding, or post-coital bleeding. With urethritis, there can be symptoms that suggest a urinary tract infection, like dysuria and frequency. If left untreated, these bacteria can ascend in the reproductive tract and cause pelvic inflammatory disease or PID- which is the inflammation of the uterus, fallopian tubes, the ovaries and of course, the cervix. Acute PID causes lower abdominal pain that worsens during sexual intercourse or sudden movement, post-coital bleeding, and intermenstrual bleeding. Chronic PID causes a low grade fever, weight loss, and abdominal pain. Sometimes, PID can be complicated by a tubo-ovarian abscess which can involve the fallopian tubes, ovaries, or other nearby pelvic organs. Now, in males, these infections can cause urethritis or epididymitis. With urethritis, there’s dysuria and penile discharge, and with epididymitis, there’s unilateral testicular pain and a hydrocele can form around the testicle. In males and females, Chlamydia trachomatis and Neisseria gonorrhoeae can also cause conjunctivitis through direct inoculation with genital secretions. If Chlamydia trachomatis and Neisseria gonorrhoeae come into contact with anal or rectal mucosa, they can cause proctitis, and symptoms include tenesmus, anorectal pain, anorectal bleeding, and constipation. Neisseria gonorrhoeae can also cause pharyngitis, leading to sore throat, pharyngeal exudates, and cervical lymphadenitis.

The gold-standard for diagnosing these infections is the nucleic acid amplification testing or NAAT from secretions. Vaginal or endocervical swabs are done for females, and urine samples or urethral swabs are done for males. If NAAT is negative for Chlamydia trachomatis and Neisseria gonorrhoeae, then NAAT is performed for Mycoplasma genitalium which is another sexually transmitted infection. In males, a Gram stain is performed on the urethral swab and is examined for the presence of white blood cells or WBCs and for bacteria. The presence of more than 2 WBCs per high power field or HPF suggests urethritis. In addition, the first-void urine should be checked and in urethritis, leukocyte esterase is positive on the dipstick test, and there are more than 10 WBC per HPF on microscopy. Finally, HIV testing is also done for all individuals.

Neisseria gonorrhoeae can be treated with a single IM dose of ceftriaxone, either 500 milligrams, in individuals that weigh less than 150kg, or 1 gram in individuals that weigh more than that. Additionally, if a Chlamydia infection has not been ruled out, doxycycline can be added to the treatment regimen, at a dose of 100 milligrams twice a day, for 7 days. For Chlamydia trachomatis infections, the same doxycycline regimen can be used, or, alternatively, a single 1 gram dose of azithromycin can be given orally, or a seven day course of levofloxacin, 500 milligrams once daily. For individuals with epididymitis or proctitis, empirical treatment for both Chlamydia trachomatis and Neisseria gonorrhoeae infection is done with a single intramuscular dose of 500 milligrams or 1 gram of ceftriaxone, depending on the person’s weight, as well as oral doxycycline, which can be given for 10 days - in the case of epididymitis, and for 7 to 21 days for proctitis depending on severity. For Mycoplasma genitalium infection, an empiric treatment regimen can be given: 100 milligrams of doxycycline twice daily for 7 days, followed by 7 days of moxifloxacin, at a dose of 400mg daily. For severe PID, treatment is 1 gram of IV ceftriaxone daily, 2 grams of IV cefoxitin twice daily, or 2 grams of IV cefotetan every 6 hours, along with 100 milligrams of oral or IV doxycycline and 500 milligrams of oral or IV metronidazole every 12 hours. After 24 hours, parenteral therapy is usually switched to oral therapy with doxycycline and metronidazole for 14 days. In case there’s a tubo-ovarian abscess, treatment is 100 milligrams of oral doxycycline twice daily, plus either 500 milligrams of oral metronidazole twice daily, or 450 milligrams of oral clindamycin 4 times a day for 14 days. For mild PID, treatment is a single dose of IM ceftriaxone and 100 milligrams of oral doxycycline and oral metronidazole twice daily for 14 days.

Okay, now moving on to Human papillomavirus infection or HPV infection and some serotypes - like 16, 18, 52 and 56- are associated with cancer. They can cause cervical, vulvar, vaginal, anorectal and oropharyngeal cancer in females and penile cancer, along with anorectal and oropharyngeal cancer in males. Now, there are some serotypes- like 6 and 11- that cause benign lesions in the genital and anal area called anogenital warts or Condylomata accuminata. Anogenital warts can be located on the vulva, penis, groin, perineum, perianal skin, and sometimes on the suprapubic skin. The warts can be single or can come in groups, can have different shapes- they can be dome-shaped, plaque-like, pedunculated, verrucous, or lobulated, and they can have different colors- they can be white, skin-colored, or erythematous. The diagnosis is made based on the appearance of the warts. If there’s any uncertainty, the wart can be biopsied. Treatment includes topical administration of imiquimod or sinecatechins. If the lesions persist, then surgical excision, electrosurgery, cryotherapy, or treatment with trichloroacetic acid can be done.

Next is Trichomonas vaginalis infection, which causes a protozoan infection called trichomoniasis. In females, symptoms include a bad-smelling, purulent and thin vaginal discharge, along with burning and pruritus in the genital area. Additionally, there can also be dysuria, frequency, lower abdominal pain, post-coital bleeding and dyspareunia- which is painful sexual intercourse. In males, the infection is usually asymptomatic, but it can cause symptoms like urethral discharge and dysuria. The gold-standard for identifying Trichomonas vaginalis is by performing NAAT on a vaginal or urethral swab. Additionally, in females, microscopy of the vaginal secretion is done and this shows motile trichomonads. Treatment in females is done with 500 milligrams of metronidazole twice daily for 7 days. In males, a single 2 gram oral dose of metronidazole can be given. An alternative regimen for all individuals consists of a single 2 gram dose or tinidazole. Recently, a similar medication called secnidazole has also been approved for the treatment of trichomoniasis, and it’s also given as a single 2 gram oral dose.

Next are infections that get transmitted through skin-on-skin contact, such as Pediculosis pubis infections- most commonly known as crabs- and Sarcoptes scabiei infections- which cause scabies. Both of these can infect the pubic area during sexual intercouse. The main symptom with both infections is pruritus that can involve the genital and perianal areas. With crabs, lice and nits- which are louse eggs- can be seen with the naked eye in the affected area. With scabies, there are usually multiple small erythematous papules. If the diagnosis is uncertain, then microscopic examination of hair shafts can confirm the diagnosis of crabs and microscopic examination of a small sample of skin can confirm scabies. Crabs and scabies can be treated with topical permethrin that’s applied until there are no more lesions in the genital area, and with crabs, the nits should be removed with a nit comb or tweezers. In addition, a first-line treatment for scabies is a single 200mg dose of oral ivermectin, followed by a repeat dose in one to two weeks. For crabs, some alternatives include topical malathion lotion or oral ivermectin.

Another example of genital infections transmitted through skin-on-skin contact is Herpes simplex virus - or HSV - infection. There are two types of herpes simplex virus- type 1 and type 2 and both can cause genital herpes. Now, the symptoms depend upon whether a person has anti-herpes simplex virus antibodies. If they don’t already have those antibodies, then it’s called a primary infection. In a primary infection, there are painful vesicles that form on an erythematous base, pruritus in the genital area, dysuria, and inguinal lymphadenopathy. Systemic symptoms include fever, headaches, and myalgias. Now, if the individual does have antibodies from a prior asymptomatic infection, then it’s called a nonprimary infection. In this case, symptoms are generally less severe. Finally, HSV can linger in the neurons and can reactivate from time to time, and when that happens the symptoms are usually more mild. Depending on the type of sexual intercourse, herpes simplex virus can also cause proctitis, which presents with tenesmus and anorectal pain.

Now, diagnosis of herpes simplex virus infection can be made with a viral culture or by doing a HSV polymerase chain reaction or HSV PCR. Serology can also be done in order to identify anti-HSV antibodies which diagnoses a past or present HSV infection. Treatment of primary and nonprimary HSV infections is done with either oral acyclovir- 400 milligrams three times daily or oral famciclovir- 250 milligrams three times daily or oral valacyclovir- 1 gram twice daily. Duration of treatment is 7 to 10 days. Treatment of recurrent HSV infections depends upon the frequency of recurrent episodes and severity of symptoms. In individuals with less than 6 recurrent episodes per year or in individuals with moderate symptoms, treatment includes oral acyclovir or oral famciclovir or oral valacyclovir for 5 days. In individuals with more than 6 recurrent episodes per year or individuals with more severe symptoms, treatment includes long-term use of oral valacyclovir 500 milligrams, oral acyclovir 400 milligrams or oral famciclovir 250 milligrams daily.

Okay, another infection that’s transmitted through skin-to-skin contact is Haemophilus ducreyi infection. It’s thought that the microabrasions in the skin that can occur during sexual contact can create a path for Haemophilus ducreyi to infect the tissues, because this bacteria doesn’t typically infect intact skin. The skin lesion starts as an erythematous papule that evolves into a painful ulcer that’s about 1 to 2 centimeters in diameter that bleeds when scraped. This is called a chancroid ulcer, and usually a few ulcers develop in the genital area. In males, there’s usually inguinal lymphadenopathy. In order to diagnose the infection, a gram stain, culture and PCR can be done using exudate from the ulcer. The gram stain can sometimes show gram-negative rods in a chain, also called “school of fish”. Treatment is a single dose of 250 milligrams of IM ceftriaxone or 1 gram of oral azithromycin.