Vaginal infection is usually characterized by a vaginal discharge or vulvar itching and irritation; a vaginal odor may be present. The three diseases most frequently associated with vaginal discharge are trichomoniasis (caused by T. vaginalis), bacterial vaginosis (caused by a replacement of the normal vaginal flora by an overgrowth of anaerobic microorganisms, mycoplasmas, and Gardnerella vaginalis), and candidiasis (usually caused by Candida albicans).
Mucopurulent cervicitis (MPC) caused by C. trachomatis or N. gonorrhoeae can sometimes cause vaginal discharge. Although vulvovaginal candidiasis and bacterial vaginosis are not usually transmitted sexually, they are included in this section because these infections are often diagnosed in women being evaluated for STDs.
The cause of vaginal infection can be diagnosed by pH and microscopic examination of the discharge. The pH of the vaginal secretions can be determined by narrow-range pH paper for the elevated pH (>4.5) typical of bacterial vaginosis (BV) or trichomoniasis.
Discharge can be examined by diluting one sample in one to two drops of 0.9% normal saline solution on one slide and a second sample in 10% potassium hydroxide (KOH) solution. An amine odor detected before or immediately after applying potassium hydroxide suggests BV. A cover slip is placed on the slides, and they are examined under a microscope at low- and high-dry power. The motile T. vaginalis or the clue cells of BV usually are identified easily in the saline specimen.
The yeast or pseudohyphae of Candida species are more easily identified in the potassium hydroxide specimen. However, their absence does not preclude candidal or trichomonal infection, because several studies have demonstrated the presence of these pathogens by using polymerase chain reaction (PCR) after a negative microscopic exam.
The presence of objective signs of external vulvar inflammation in the absence of vaginal pathogens, along with a minimal amount of discharge, suggests the possibility of mechanical, chemical, allergic, or other noninfectious irritation of the vulva. Culture for T. vaginalis is more sensitive than microscopic examination. Laboratory testing fails to identify the cause of vaginitis among a minority of women.