Smelly Intercourse Without Discharge in a 50-Year-Old Woman
The most likely cause is bacterial vaginosis that was missed on initial testing, and you should retest using Gram stain with Nugent criteria, which has 90% sensitivity compared to standard clinical testing that misses 20-30% of BV cases. 1, 2
Why Bacterial Vaginosis is the Primary Suspect
Even without visible discharge, BV remains the most probable diagnosis because:
- BV accounts for 40-50% of all identified vaginitis cases and is the most common cause of malodorous vaginal discharge 1, 2, 3
- Up to 50% of women with BV meeting diagnostic criteria are asymptomatic or have minimal symptoms, meaning the infection can be present without classic discharge 1, 2
- Standard clinical testing misses 20-30% of BV cases, making missed diagnosis the most likely explanation for persistent odor with negative initial workup 1, 2
- The characteristic fishy/foul odor during intercourse occurs because semen (which is alkaline) releases volatile amines produced by anaerobic bacteria in BV 3
Diagnostic Algorithm
Step 1: Retest for BV using superior methods
- Order Gram stain with Nugent criteria scoring (90% sensitivity, most specific method) 1, 2
- Alternative: DNA probe testing for Gardnerella vaginalis has similar accuracy to Gram stain 3
- Measure vaginal pH: BV produces pH >4.5, which helps differentiate from candidiasis (pH <4.5) 2, 4
Step 2: If BV is confirmed on retesting
- Treat with metronidazole 500 mg orally twice daily for 7 days (cure rate 80-90%, superior to single-dose regimens) 1, 2
- The 7-day regimen achieves 95% cure rates compared to 84% with single 2g dose 1
- Counsel about 50-80% recurrence rate within one year 1, 2
Special Considerations for a 50-Year-Old Woman
Atrophic vaginitis must also be considered in this postmenopausal age group:
- Vaginal dryness and atrophic changes are frequently reported during menopause 5
- Atrophic vaginitis can alter vaginal pH and flora, potentially contributing to odor 5
- If BV testing remains negative and symptoms persist, consider trial of local estrogen therapy, which has excellent therapeutic response for vulvovaginal symptoms 5
Common Pitfalls to Avoid
- Do not rely on clinical appearance alone: 75% of women with BV report never noting vaginal odor in the past 6 months, and 58% report no discharge 6
- Do not assume candidiasis: While candidiasis can present with white discharge, it typically causes pruritus and has normal pH <4.5, not malodor 4
- Do not treat empirically without retesting: The CDC recommends against treating asymptomatic patients with incidental findings, as this leads to inappropriate antibiotic use 1
- Do not forget partner notification if BV confirmed: Though not sexually transmitted, sexual activity can disrupt vaginal flora 7