What does the presence of anaerobic overgrowth, positive White Blood Cells (WBCs), and epithelial cells, along with the absence of visible microbes, indicate?

Interpretation of Anaerobic Overgrowth with WBCs, Epithelial Cells, and Negative Microbes

This pattern most likely indicates bacterial vaginosis (BV) or a contaminated specimen, depending on the specimen source and clinical context. If this is a vaginal specimen with clinical symptoms, the presence of anaerobic overgrowth with WBCs strongly suggests bacterial vaginosis, which is characterized by overgrowth of anaerobic bacteria displacing normal lactobacilli 1. The absence of visible microbes on routine microscopy does not exclude anaerobic infection, as anaerobes are technically demanding to detect and often require specific transport conditions and culture techniques 2, 3.

Clinical Context Determines Interpretation

If Vaginal/Cervical Specimen:

• Bacterial vaginosis is the primary consideration when anaerobic overgrowth is documented with WBCs present 1
• The presence of WBCs on microscopic evaluation of vaginal fluid is a supportive criterion for pelvic inflammatory disease (PID), which frequently involves anaerobic bacteria 1
• Anaerobic bacteria have been isolated from the upper reproductive tract of women with PID, and certain anaerobes like Bacteroides fragilis can cause tubal and epithelial destruction 1
• BV is present in many women who have PID, making anaerobic coverage essential in treatment regimens 1

If Wound/Abscess Specimen:

• Contaminated or dirty wounds contain anaerobic organisms in 65-94% of samples, even when routine cultures appear negative 2, 3
• The presence of epithelial cells suggests possible contamination with skin flora 1
• Foul-smelling discharge, gas formation, necrotic tissue, and abscess formation are characteristic of anaerobic infections 3
• Infections in proximity to mucosal surfaces where anaerobes are part of normal flora should raise suspicion 3, 4

Why Microbes May Not Be Visible

Technical Limitations:

• Detection of anaerobic organisms is technically demanding and may require specific measures such as transporting specimens in anaerobic conditions 2, 3
• Anaerobes are difficult to culture and require appropriate methods of collection, transportation, and cultivation 4, 5
• Gram-stained smears should be standard for all anaerobic cultures to evaluate specimen adequacy and provide early presumptive diagnosis 3
• Aspirate or biopsy of inflammatory material is preferred over swabs, and specimens must be placed into anaerobic transport containers 3

Specimen Contamination:

• A urine sample with more than 10 WBCs and a significant number of epithelial cells must be considered contaminated 1
• High epithelial cell counts indicate periurethral or skin contamination rather than true infection 1

Critical Diagnostic Approach

Immediate Actions:

• Correlate with clinical presentation: fever, pain, discharge characteristics, odor 1
• Assess specimen adequacy: high epithelial cells suggest contamination requiring repeat collection 1, 3
• Request specific anaerobic cultures if not already performed, with proper anaerobic transport 2, 3
• Consider fungal and mycobacterial cultures if epidemiologic risk factors present 1

Specimen Re-collection if Contaminated:

• Use proper collection technique to minimize epithelial cell contamination 1
• For suspected infection, obtain aspirate or biopsy rather than swabs 3
• Ensure anaerobic transport containers are used 3, 5

Treatment Implications

If Clinical Infection Suspected Despite Negative Microscopy:

• Empiric broad-spectrum coverage including anaerobes should be initiated for contaminated/dirty wounds or suspected PID 1, 2
• Most effective antimicrobials against anaerobes include metronidazole, carbapenems (imipenem, meropenem, ertapenem), or combinations of penicillin with beta-lactamase inhibitors 5, 6, 7
• For PID, treatment regimens must provide coverage of N. gonorrhoeae, C. trachomatis, anaerobes, Gram-negative facultative bacteria, and streptococci 1

Source Control:

• Drainage of abscesses, decompression of infected spaces, and debridement of necrotic tissue are critical in management of anaerobic infections 4, 5
• Antimicrobial therapy is often an important adjunct to surgical drainage 5, 6

Common Pitfalls to Avoid

• Do not rely solely on aerobic cultures or routine microscopy in appropriate clinical scenarios, as this leads to missed anaerobic diagnoses 2, 3
• Do not assume absence of infection based on negative routine microscopy when clinical features suggest anaerobic involvement 2, 3
• Do not dismiss specimens with high epithelial cells without considering contamination and obtaining proper repeat specimen 1
• Do not delay empiric anaerobic coverage when clinical presentation suggests infection, even with negative initial microscopy 1, 2