What infections can cause sinus tracts?

Infections That Can Cause Sinus Tracts

The most common infections causing sinus tracts are chronic bacterial osteomyelitis and chronic odontogenic (dental) infections, with Staphylococcus aureus being the predominant pathogen in bone infections and mixed oral flora in dental infections.

Bacterial Infections

Chronic Osteomyelitis

Chronic osteomyelitis is the classic cause of draining sinus tracts, particularly in long bones and the axial skeleton. A draining sinus should prompt high clinical suspicion for chronic bone infection 1. The persistent bone infection results in continuous soft tissue infection with consequent formation of a sinus tract to allow pus drainage through the skin 1.

Key pathogens include:

• Staphylococcus aureus (most common)
• Gram-negative organisms (Pseudomonas aeruginosa, Klebsiella, Enterobacter, Proteus, Serratia)
• Anaerobes (Prevotella species, Fusobacterium)
• Polymicrobial infections (associated with higher risk of sinus tract formation) 2

Important clinical correlation: Sinus tract cultures have been shown to have 96% specificity and 90% predictive value compared with operative bone specimens, making them a reliable source for identifying causative bacteria except for Staphylococcus epidermidis 3. When osteomyelitis is monomicrobial, sinus tract cultures are particularly accurate 3.

Odontogenic Infections

Chronic dental infections are the most common cause of cutaneous sinus tracts in the face and neck region 4, 5, 6. These develop from:

• Dental caries with pulp necrosis leading to chronic periapical abscess (most common) 7
• Periodontal disease
• Dental trauma

Critical diagnostic pitfall: These are frequently misdiagnosed as primary skin lesions because overt dental symptoms may be absent, leading to unnecessary surgical excisions, biopsies, long-term antibiotics, or even radiation therapy 6. The key diagnostic clues are chronicity (lasting weeks to years) and recognition of the lesion as a sinus tract rather than a primary cutaneous process 6.

Sinusitis-Related Bacterial Infections

While the provided guidelines focus primarily on sinusitis as inflammation of paranasal sinuses rather than sinus tract formation, chronic bacterial sinusitis can occasionally lead to complications with fistula formation. The common bacterial pathogens include 8:

• Streptococcus pneumoniae
• Haemophilus influenzae
• Moraxella catarrhalis
• Staphylococcus aureus
• Anaerobes (Prevotella, Fusobacterium) in chronic cases
• Gram-negative enterics (Pseudomonas aeruginosa) in nosocomial or chronic cases

Fungal Infections

Invasive Fungal Sinusitis

Invasive fungal sinusitis occurs almost exclusively in immunocompromised patients and can lead to tissue destruction with potential fistula formation 8. This fulminant disease is seen in:

• Diabetic patients (especially with mucormycosis)
• Febrile neutropenic patients with leukemia or solid malignancies
• Patients on high-dose steroids (transplant recipients, connective tissue disease)
• Severe T-cell immunodeficiency (transplant, HIV, congenital)

Common fungal pathogens:

• Mucorales (in diabetics - formerly called mucormycosis)
• Aspergillus species (in hematological malignancies)
• Bipolaris, Curvularia, Dreschlera species 8, 9

Clinical presentation includes: fever, headache, epistaxis, mental status changes, and insensate nasal ulcers 8. This requires aggressive debridement and systemic antifungal therapy 8.

Chronic Invasive Fungal Sinusitis

Less fulminant forms exist, including chronic invasive fungal sinusitis and granulomatous invasive fungal sinusitis, which can develop sinus tracts over time 9.

Clinical Risk Factors for Sinus Tract Formation

Based on recent quantitative analysis, sinus tract formation in infectious joint disease (which parallels osteomyelitis) is associated with 2:

• Malnutrition (OR = 1.92)
• Gram-positive infections (OR = 4.92)
• Polymicrobial infections (OR = 6.37)
• Multiple previous surgeries (mean difference of 1.12 surgeries)
• Longer duration of infection (>1 month increases surgical history)

Diagnostic Approach

For suspected osteomyelitis with draining sinus:

1. Obtain radiographs first 1
2. Culture the sinus tract drainage (reliable except for S. epidermidis) 3
3. Consider MRI or CT for extent of bone involvement 1
4. Blood cultures are unlikely to be positive in chronic osteomyelitis unless the patient is critically ill 3

For facial/neck cutaneous sinus tracts:

1. Always consider odontogenic origin first - examine for dental caries, periodontal disease, or history of dental trauma 4, 6
2. Obtain dental radiographs or panoramic imaging
3. Refer to endodontist if dental etiology suspected
4. Root canal treatment alone (without surgical excision) typically leads to complete resolution 4, 5

Common pitfall: Chronicity lasting weeks to years is the key to recognizing these as sinus tracts rather than acute abscesses or primary skin lesions 6.