Vaginal Infections — Causes, Symptoms, Diagnosis & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Vaginal infections are among the most common reasons for gynaecological consultation, affecting the majority of women at some point during their reproductive lives. The healthy vaginal ecosystem is dominated by Lactobacillus species (predominantly L. crispatus and L. iners) that maintain a low pH of 3.8-4.5 through lactic acid production, providing protection against pathogen overgrowth. Disruption of this protective flora underpins most vaginal infections. The three most clinically important entities are: bacterial vaginosis (BV — 40-50% of presentations — a polymicrobial dysbiosis, not a true infection), vulvovaginal candidiasis (VVC/thrush — 20-25% — Candida overgrowth), and trichomoniasis (Trichomonas vaginalis — 15-20% — a sexually transmitted protozoan infection). Accurate diagnosis through symptom assessment, pH testing, and microscopy is essential as treatment differs completely between these conditions — empirical antifungal treatment is incorrect in over 50% of women who self-diagnose thrush.

Bacterial vaginosis (BV): disruption of the normally Lactobacillus-dominant vaginal flora with polymicrobial anaerobic overgrowth — principally Gardnerella vaginalis (the most abundant organism in BV), Prevotella species, Mobiluncus species, Fannyhessea vaginae (formerly Atopobium vaginae), and Mycoplasma hominis. The shift from Lactobacillus dominance to polymicrobial dysbiosis occurs when vaginal pH rises above 4.5, allowing competitive overgrowth of non-Lactobacillus organisms. Risk factors: new or multiple sexual partners (sexual activity is the major risk factor — though BV is not formally classified as an STI, female-to-female sexual transmission is documented); vaginal douching (the most modifiable risk factor — disrupts protective flora and elevates pH); cigarette smoking; copper intrauterine device (IUD) use; menstruation (alkaline menstrual blood raises pH); and African-Caribbean ethnicity (higher baseline BV prevalence in epidemiological studies). Vulvovaginal candidiasis (VVC/thrush): overgrowth of Candida albicans (85-90% of VVC episodes); non-albicans Candida species (C. glabrata, C. tropicalis, C. krusei — associated with recurrent VVC and reduced azole sensitivity). Conditions promoting Candida overgrowth: antibiotics (the most common trigger — broad-spectrum antibiotics eliminate competing bacterial flora); diabetes mellitus (hyperglycaemia promotes vaginal Candida growth — recurrent VVC without other risk factors should prompt HbA1c testing); immunosuppression (HIV, corticosteroids, chemotherapy); high-oestrogen combined OCP (promotes vaginal glycogen deposition — a Candida nutrient substrate); and pregnancy (elevated oestrogen and progesterone). Trichomoniasis: caused exclusively by the sexually transmitted protozoan Trichomonas vaginalis — transmitted by sexual contact; incubation period 5-28 days; asymptomatic in 10-50% of infected women; all sexual partners within 6 months must be tested and treated simultaneously.

Bacterial vaginosis (BV): thin, homogeneous, grey-white or off-white vaginal discharge that uniformly coats the vaginal walls; characteristic malodorous fishy (amine) smell markedly worse immediately after unprotected intercourse (seminal fluid raises vaginal pH, releasing volatile amines — putrescine and cadaverine — from anaerobic bacterial metabolism) and after menstruation; importantly, typically no vulval pruritus or soreness — absence of itch is a key differentiating feature from VVC; the Amsel clinical diagnostic criteria require at least 3 of 4: (1) homogeneous grey-white discharge, (2) vaginal pH above 4.5 on litmus paper, (3) positive amine whiff test (fishy odour when 10% KOH is added to the discharge), and (4) clue cells above 20% on wet preparation microscopy (vaginal epithelial cells uniformly coated with adherent bacteria, obscuring the cell border). Vulvovaginal candidiasis (VVC/thrush): thick, white, curd-like or cottage cheese discharge without offensive odour; severe vulval pruritus (itching) — the dominant and most distressing symptom; vulval soreness, burning, and erythema of the vaginal introitus and labia minora; superficial dyspareunia; external dysuria (burning as urine contacts inflamed labia); normal vaginal pH below 4.5 — this is an important differentiating feature from BV and trichomoniasis. Trichomoniasis: profuse, yellow-green, frothy or bubbly, malodorous purulent discharge — the frothy quality is characteristic; strawberry cervix (colpitis macularis — punctate cervical haemorrhages visible on speculum examination — present in only 2-10% but highly specific when seen); strong, unpleasant vaginal odour; dysuria; vulval pruritus; and lower abdominal discomfort. Up to 50% of T. vaginalis infections in women are asymptomatic, making partner notification and testing important.

High vaginal swab (HVS) for microscopy and culture. BV: Amsel criteria — clinical diagnosis (3 of 4 positive: homogeneous grey discharge, pH above 4.5, positive amine whiff test with 10% KOH, above 20% clue cells on microscopy) or Nugent score (Gram stain microscopy — gold standard for research); pH above 4.5. VVC: wet preparation (hyphae and spores on KOH microscopy); culture on Sabouraud's medium for speciation; pH below 4.5. Trichomoniasis: wet prep (motile trichomonads — sensitivity only 60-70%); NAAT most sensitive (above 95%); pH above 4.5. NAAT also screens for concurrent STIs (chlamydia, gonorrhoea). Point-of-care NAAT: simultaneous testing for BV-associated organisms, Candida species, Trichomonas vaginalis, chlamydia, and gonorrhoea from a single swab — reduces empirical treatment errors. Vaginal pH testing (litmus paper): BV and trichomoniasis give pH above 4.5; candidiasis gives normal pH below 4.5 — a useful primary care triage step. Amine (whiff) test: 10% KOH applied to discharge produces a characteristic fishy amine odour in BV (from release of putrescine and cadaverine).

BV: metronidazole 400 mg BD orally for 5-7 days; or metronidazole 0.75% gel intravaginally once daily for 5 days; or clindamycin 2% cream intravaginally for 7 nights. Recurrent BV (≥4 episodes/year): metronidazole 400 mg BD for 5-7 days followed by 0.75% metronidazole gel twice weekly for 4-6 months. VVC (uncomplicated): fluconazole 150 mg oral single dose (safe, effective) or clotrimazole 500 mg pessary single dose. Recurrent VVC (≥4 episodes/year): fluconazole 150 mg weekly for 6 months maintenance. Trichomoniasis: metronidazole 2g single dose (patient and partner simultaneously); or metronidazole 400 mg BD for 5-7 days if compliance concern. Regular monitoring of treatment response, early detection of side effects, and ongoing assessment of disease progression are essential components of optimising patient outcomes over the long term. Treatment plans should be proactively reviewed and appropriately adjusted based on clinical response, patient-reported tolerability, changing patient circumstances, and continuously evolving evidence-based clinical guidelines. Meaningful shared decision-making between patients and their healthcare team, incorporating patient values and treatment preferences, consistently improves both treatment adherence and long-term outcomes.

BV: increased acquisition of HIV (2x), HSV, chlamydia, gonorrhea, and HPV. In pregnancy: BV associated with preterm birth (PPROM, preterm labor) and postpartum endometritis. VVC: recurrent (complicated) VVC causes significant psychosocial impact, dyspareunia, and relationship strain; rare vulval scarring. Trichomoniasis: increased HIV transmission and acquisition; in pregnancy: preterm delivery and low birth weight; increased risk of cervical cancer (co-infection with HPV). Long-term specialist follow-up and structured regular review are essential to detect and appropriately manage complications at the earliest possible stage, minimising long-term disability, preserving organ function, and improving the overall prognosis. Patient education about the early warning signs of complications and clear guidance on when to seek urgent medical attention empowers timely help-seeking behaviour and reduces preventable serious adverse outcomes. Psychological impact — including depression, anxiety, and reduced quality of life — should be proactively assessed and addressed as part of comprehensive complication management.

Avoid vaginal douching (disrupts protective Lactobacillus flora). Use condoms (reduces BV and trichomoniasis). Wear breathable cotton underwear. Limit antibiotic use to when clinically necessary (prevents VVC). Maintain good blood glucose control (reduces candidal overgrowth). After BV treatment, Lactobacillus probiotics (oral or vaginal) may reduce recurrence. Treat partners simultaneously for trichomoniasis (re-infection is the most common cause of treatment failure). Sustained lifestyle modifications — maintaining a healthy body weight through balanced diet and regular physical activity, avoiding tobacco smoking, limiting alcohol intake, and managing chronic conditions such as hypertension and diabetes — are foundational strategies for reducing the risk of this condition and its complications. Regular health screening in at-risk populations, rigorous adherence to prescribed preventive medications, and proactive monitoring of established risk factors are equally critical and complementary components of a comprehensive and effective long-term prevention strategy.

See your GP or a sexual health (GUM) clinic for: vaginal discharge that is new, different from usual, persistent for more than 1-2 weeks, or associated with unusual odour, itching, soreness, or painful urination. A single episode of vaginal thrush with classic symptoms in a low-risk healthy woman is appropriate for self-treatment with OTC clotrimazole or fluconazole — but see a GP if symptoms do not resolve within 7 days of self-treatment or recur more than 4 times per year. Attend a GUM clinic for: any possible STI risk (new partner, unprotected intercourse), or if trichomoniasis is confirmed — this requires partner notification and simultaneous treatment. Seek urgent medical assessment for: lower abdominal or pelvic pain with vaginal discharge and fever (possible pelvic inflammatory disease — PID — which requires same-day assessment, IV antibiotics if systemically unwell, and treatment of partners to prevent reinfection); vaginal discharge in pregnancy (some infections including BV, trichomoniasis, and group B streptococcus increase the risk of preterm birth and require prompt treatment); or postmenopausal vaginal bleeding with discharge (requires urgent gynaecology referral to exclude endometrial pathology — do not attribute postmenopausal bleeding to infection without investigation).