Gram stain as a relapse predictor of bacterial vaginosis after metronidazole treatment

Bacterial vaginosis is the most prevalent disease of the female genital tract. In spite of various effective antibiotics in the treatment of bacterial vaginosis, its high relapse rate is a common problem. Bacterial species causing bacterial vaginosis are generally unable to be cultured by conventional methods. It is impractical and inadequate to use culture methods to guide initial treatment. Gram stain of vaginal secretion is a practical tool to establish the diagnosis of bacterial vaginosis. We enrolled 78 cases of Gram stain-proven bacterial vaginosis and tried to use Gram stain as a predictor of relapse after 1 week of treatment with metronidazole. Possible predictive factors for relapse in Gram stain were analyzed, including absence of large Gram-positive rods, presence of small Gram-negative rods, small Gram-variable rods, curved Gram-variable rods, or Gram-positive cocci. Gram stain was repeated immediately after treatment, and at 1 month and 3 months after treatment. All cases showed beneficial clinical effect after metronidazole treatment. Eighteen cases (23.1%) relapsed during the follow-up period. All 16 cases with significant Gram-positive cocci in pretreatment smears relapsed after metronidazole treatment. Presence of small Gram-negative rods, small Gram-variable rods, and curved Gram-variable rods, or absence of large Gram-positive rods did not predict relapse. Gram-positive cocci in pretreatment smear was a good predictor of relapse after metronidazole treatment.