Know your STD's baby ;-) (going through every other choice on this question):
Bacterial vaginosis caused by gardnerella vaginallis. Se a thin, off white discharge and fishy smell (fish in the garden). There's no inflammation Lab findings: pH greater than 4.5 (just like trichomoniasis), and a positive whiff test with KOH. Stem will say something about malodorous discharge and show the infamous CLUE CELLS if we are lucky. Not the answer for this question obviously because we would not expect vesicles with this bacterial disease.
Candidiasis is going to be your thick cottage cheese discharge, with inflammation. normal pH see pseudohyphae. Treat with topical nystatin, or oral fluconazole unless you're pregnant than use Clotrimazole. Again not going to see any vesicles.
Chancroid per uworld is associated with Haemophilus ducreyi you will have a Deep purulent painful ulcer with suppurative lymphadenitis. Will be told that patient has painful inguinal nodes, there may be multiple deep ulcers with gray-yellow exudate. You do cry with H. duCRYi This wouldn't be true for what our patient has in this question because we aren't told of any inguinal adenopathy. a link to a chancroid VDA
Chlamydia trachomatis causes lymphogranuloma venereum which is small shallow ulcers, painless, but then the large painful coalesced inguinal lymph nodes aka BUBOES. Compared with gonnorhea the discharge is more thinner and watery. Again not the case here as its painful and no mention of any BUBOOESS. The discharge in gonorrhea is more thicker. Both lead to PID, treat for both because confection is common. With both patient may have some sort of pain or burning sensation upon urination. Sterile pyuria though for both.
Condyloma accuminatum is a manifestation of HPV 6 + 11 (genital warts). They look like big cauliflowers. This is in contrast to Condyloma lata that you see in syphillis which is just a flatter latte brown looking macule.
Genital Herpes (the answer to the question) will present with multiple painful superficial vesicles or ulcerations with constitutional symptoms (fever, malaise) Just fits better than all the other choices I ran through.
Syphillis is the painless chancre. UW describes it as a single, indurated well circumscribed ulcer, with a clean base. See corkscrew organisms on DF microscopy. Keep in mind other painless ulcers are lymphogranuloma venereum of clamydia (but the buboes are whats painful not the ulcer), and granuloma inguinale (donovanosis - klebsiella granulomatis) but whats hallmark about this one is that its painless without lymphadenopathy
In short, be safe.
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