Bacterial vaginosis is the most common cause of vaginitis, affecting over 3 
million women in the United States annually. Depopulation of lactobacilli from 
the normal vaginal flora and overgrowth of Gardnerella vaginalis and other 
anaerobic species are the presumed etiology. To date, no scientific evidence 
shows that bacterial vaginosis is a sexually transmitted disease. Malodorous 
vaginal discharge is the most common symptom. Differential diagnoses include 
trichomoniasis, moniliasis, and allergic or chemical dermatitis. The diagnosis 
is confirmed when at least three of the following four findings are present 
(Amsel's criteria): 1) thin, homogenous discharge, 2) pH greater than 4.5, 3) 
positive amine test, and 4) presence of clue cells. The sensitivity and positive 
predictive value are both 90%. Vaginal Gram stain is also reliable and allows 
for permanent record. Cultures are nonspecific because G. vaginalis resides in 
normal vaginal flora as well. Papanicolaou smears are not particularly 
sensitive, but their positive predictive value is very high. The Centers for 
Disease Control and Prevention recommend three treatment regimens in nonpregnant 
patients: oral metronidazole (500 mg twice daily for 7 days), intravaginal 2% 
clindamycin cream (one applicatorful at bedtime for 7 days), or intravaginal 
metronidazole gel (one to two applicatorfuls per day for 5 days). Alternative 
regimens include a single 2-g oral dose of metronidazole or a 7-day course of 
oral clindamycin, 300 mg twice daily. The association between bacterial 
vaginosis and adverse pregnancy outcomes has satisfied many criteria for a 
causal inference. Treatment of bacterial vaginosis in women with previous 
history of preterm labor results in fewer preterm deliveries than in untreated 
women from the same population.