Cause:(Med Let 1999;41:86) Gardnerella vaginalis, Mobiluncus, mycoplasmas, ureaplasmas, and other anaerobes, which themselves may be primary cause. These are all endogenous flora, not necessarily venereal since occur in 15% of virginal women
Pathophys:Diminished presence of lactobacilli, corresponding increase in pH leading to G. vaginalis, Mycoplasma hominis(Nejm 1995;333:1732, 1737), and anaerobe (esp Bacteroides) overgrowth
3rd most common cause of vaginitis after trichomonas and monilia
Sx:Vaginitis with watery discharge, no dyspareunia
Si:Watery discharge evenly coats walls; vinegar-like smell
Increased incidence of premature labor (<37 wk) and low birth weight
r/o trichomonal (Trichomonas Urethritis/Vaginitis), monilial (Candidiasis (Moniliasis, Local) (Including Vaginal)), and other (Vaginitis Causes) vaginitis causes
Lab:Bact:Vaginal discharge smear shows clue cells (100%—Lancet 1983;2:1379); pH >4.5-5.0; positive amine ("whiff") test, ie, discharge smells of ammonia (70-80%); few polys. Culture positive in 40%
Rx:
(Med Let 1994;41:86)
Preventive: unclear if screening as rx asx pregnant women decr prematurity and LBW babies (Am J Prev Med 2001;20[3S]:62); rx at least women at high risk for preterm labor since rx decreases incidence from 50% to 30% (Nejm 1995;333:1732 vs 2000;342:534, 581)
of disease (Ann IM 2002;137:255):
- Metronidazole (Flagyl) 2 gm qd × 1
75% cure; or 500 mg bid × 7 d 
95% cure (Lancet 1983;2:1379), costs $5; 30% recur in 1 mo, at least if partner not rx'd, although partner rx not clearly helpful (Ann IM 1989;111:551). Or as metronidazole vaginal gel 5 gm qd × 5 d, costs $20; or - Tinidazole 2 gm po daily × 2 (Med Let 2007;49:73); or
- Clindamycin 300 mg po bid × 7 d; or as 2% vag cream 5 gm q hs × 7 d; costs $27
in pregnancy: metronidazole 250 po tid × 7 d, or clindamycin po as above