Aerobic vaginitis (AV) is a vaginal infection caused by an overgrowth of aerobic bacteria that normally live in the intestinal tract. It’s distinct from the more commonly known bacterial vaginosis (BV), though the two are often confused. AV involves significant inflammation of the vaginal walls, something BV does not cause, and it can lead to serious complications during pregnancy if left untreated.
How AV Develops
A healthy vagina is dominated by lactobacilli, bacteria that produce lactic acid and keep the environment acidic enough to suppress harmful organisms. In aerobic vaginitis, these protective bacteria decline or disappear, and aerobic bacteria from the gut move in and multiply. The most common culprits are Group B Streptococcus, E. coli, Staphylococcus aureus, Klebsiella pneumoniae, and Enterococcus faecalis.
These bacteria produce toxins and trigger an immune response in the vaginal lining, leading to visible inflammation. This is the hallmark of AV: it’s not just a shift in bacterial populations, but an active infection that damages tissue.
Symptoms of Aerobic Vaginitis
AV can produce a wide range of symptoms, and their severity varies. The most common include:
- Purulent or yellow discharge, sometimes thick and cottage cheese-like
- Vulvar itching and burning pain
- Stinging or soreness in and around the vagina
- Pain during sex (dyspareunia)
- Redness and swelling of the vaginal walls, sometimes with small erosions or ulcerations
These symptoms tend to be persistent and progressive, meaning they typically won’t clear up on their own. The inflammation and tissue disruption can make sex painful enough to avoid entirely, which has a significant impact on quality of life.
How AV Differs From Bacterial Vaginosis
AV and BV share one key feature: both involve a loss of healthy lactobacilli. But the similarities largely end there. BV is caused by anaerobic bacteria (organisms that thrive without oxygen) and produces a thin, grayish discharge with a characteristic fishy odor. It does not cause inflammation. Under a microscope, BV shows a granular pattern of bacteria coating the vaginal cells.
AV, by contrast, is driven by aerobic bacteria (organisms that need oxygen) and causes obvious inflammation: redness, swelling, and sometimes open sores on the vaginal walls. The discharge is typically yellow or purulent rather than gray. Vaginal pH is elevated in both conditions, but it tends to be even higher in AV. Microscopically, AV shows white blood cells flooding the tissue and immature epithelial cells called parabasal cells, signs that the vaginal lining is under active attack. None of these inflammatory markers appear in BV.
This distinction matters because the treatments are different. Antibiotics that work for BV often won’t resolve AV.
How Common Is AV?
AV is less common than BV but far from rare. In a study of nearly 3,000 symptomatic, non-menopausal women, about 4.7% had purely aerobic infections. An additional 3.4% had mixed infections where aerobic bacteria were dominant, and another 9% had mixed infections with both aerobic and anaerobic organisms present. By comparison, purely anaerobic infections (the BV pattern) accounted for about 83% of cases.
Because AV wasn’t formally described until 2002, it remains underdiagnosed. Many cases are likely misclassified as BV or yeast infections, especially in settings where microscopic evaluation isn’t routine.
How AV Is Diagnosed
Diagnosis relies on microscopic examination of a vaginal sample combined with clinical signs. The most widely used approach is a composite scoring system that evaluates five factors: the number of remaining lactobacilli, the concentration of white blood cells, whether the background bacteria appear as cocci or chains (rather than normal rod-shaped bacteria), the proportion of immature epithelial cells, and clinical features like vaginal redness, yellow discharge, and pH above 4.5.
Each factor is scored from 0 to 2, producing a total between 0 and 10. A score of 4 or higher indicates AV. Scores of 4 to 5 correspond to mild AV, 6 to 7 to moderate, and 8 to 10 to severe. This scoring system helps clinicians distinguish AV from BV and gauge how aggressively to treat it.
Treatment Options
Treatment depends on severity. For most cases, topical antibiotics applied directly in the vagina are the first choice. The ideal topical antibiotic is one that isn’t absorbed into the bloodstream and covers a broad range of both gram-positive and gram-negative aerobic bacteria. Kanamycin, applied locally, fits this profile well.
For more severe infections, particularly deep vulvar inflammation or cases involving Group B Streptococcus or drug-resistant Staphylococcus, oral antibiotics may be needed for faster symptom relief. The goal of oral treatment is short-term control of severe symptoms before transitioning to local management.
Restoring the vaginal lactobacilli after clearing the infection is an important part of recovery. Probiotic strains isolated from healthy vaginal flora, particularly Lactobacillus crispatus and Lactiplantibacillus plantarum, have shown promise in animal studies. In one study, combining these two strains reduced vaginal swelling, lowered inflammatory markers, and helped restore the protective mucosal barrier. Probiotic therapy is generally used as a follow-up to antibiotics rather than a standalone treatment.
AV During Pregnancy
Aerobic vaginitis carries meaningful risks during pregnancy. Multiple studies have found significantly higher rates of preterm birth, premature rupture of membranes, neonatal jaundice, and neonatal infection in pregnant women with AV compared to those without it.
The most concerning data involves a specific subtype where cocci-shaped bacteria dominate the vaginal flora. This pattern has been associated with a 3.2 times higher risk of extremely preterm birth and a 5.2 times higher risk of miscarriage. A study of 685 pregnant women found that all four major complications, preterm birth, premature rupture of membranes, neonatal jaundice, and neonatal infection, were significantly more common in the AV group. Another study of 600 women in late pregnancy confirmed a strong link between AV and preterm delivery.
These findings make screening and treatment of AV particularly important during pregnancy, though routine screening is not yet standard practice in most countries.