Could the Aspergillus (a type of fungus) in the second sample be contamination or a true positive in a patient with a history of necrotizing granulomatous inflammation, possibly indicating tuberculosis (TB), and a delayed laboratory processing time of 6 days?

Aspergillus in Delayed Sacroiliac Biopsy: True Infection vs. Contamination

The Aspergillus growth in the second sample is most likely a true positive representing genuine infection rather than contamination, despite the 6-day delay, because the organism was confirmed by both culture growth and positive histopathological staining (PAS and GMS), which together provide strong evidence of true fungal presence even in the absence of granulomas. 1

Key Diagnostic Considerations

Evidence Supporting True Infection

• Positive histopathological staining (PAS and GMS) combined with culture growth strongly indicates true infection rather than contamination, as contamination typically does not produce positive tissue staining 1
• The presence of Aspergillus hyphae on microscopy from a percutaneous biopsy specimen is considered sufficient for confirmed diagnosis of aspergillosis, even without granulomas 1
• Aspergillus can coexist with mycobacterial infections (TB or NTM), and diagnosing one does not exclude the other 1

Clinical Context Matters

• The first sample showed necrotizing granulomatous inflammation suggesting TB, which creates the exact predisposing condition for chronic necrotizing aspergillosis 2, 3
• Chronic necrotizing pulmonary aspergillosis (CNPA) characteristically occurs in patients with preexisting pulmonary disease or altered local defense mechanisms, making this clinical scenario highly plausible 2, 3
• The absence of granulomas in the second sample does not rule out aspergillosis; histological features can vary, and tissue invasion by Aspergillus with necrosis is the key finding 1, 3

Addressing the 6-Day Delay Concern

Why Delay Doesn't Necessarily Mean Contamination

• Aspergillus DNA and antigens remain stable in tissue samples over time, unlike the more labile nature of some other diagnostic markers 4
• The combination of positive culture AND positive histopathological staining makes environmental contamination highly unlikely, as contamination would typically affect only culture, not tissue staining 1
• If this were contamination, you would expect to see fungal elements without the tissue context or inflammatory response, but the presence of hyphae visible on PAS/GMS staining indicates tissue presence 1, 3

Common Pitfalls to Avoid

• Do not dismiss positive Aspergillus findings simply because of processing delays - the combination of culture and histopathology is diagnostic regardless of timing 1
• Do not assume that absence of granulomas rules out fungal infection; granulomatous response is variable and depends on host immune status 1, 3
• Contamination of blood collection tubes and respiratory samples with Aspergillus DNA has been documented 5, but tissue biopsy specimens with positive histopathology are far less susceptible to this issue

Recommended Diagnostic Algorithm

Immediate Steps

1. Obtain serum Aspergillus antibody testing (precipitins or IgG) - this is critical for confirming chronic aspergillosis and differentiates infection from colonization with 100% positive predictive value 1
2. Consider serum galactomannan testing, though it has lower sensitivity (23-66%) for chronic forms compared to invasive aspergillosis 1
3. Review the patient's immune status, underlying conditions (diabetes, COPD, prior TB, malnutrition, alcohol use), as these predispose to chronic necrotizing aspergillosis 2, 3

Confirmatory Testing

• If Aspergillus antibodies are positive, this confirms true infection rather than contamination 1
• Request review of the histopathology to determine if hyphae are invading tissue (indicating invasive/semi-invasive disease) versus simply present in a cavity 1
• Assess for evidence of tissue necrosis and inflammatory response on pathology, which supports true infection 3

Clinical Implications and Management

Treatment Considerations

• If this represents true chronic necrotizing aspergillosis (semi-invasive aspergillosis), itraconazole is the preferred initial therapy due to documented efficacy and minimal toxicity 2
• Voriconazole or isavuconazole are alternative first-line options for invasive or semi-invasive aspergillosis 1
• The dose and duration should be based on clinical response, with consideration for chronic maintenance therapy if residual disease persists 2

Dual Infection Management

• Treat both TB (if confirmed) and aspergillosis concurrently, as they can coexist 1
• Monitor for drug interactions between anti-TB medications and azole antifungals, particularly rifampin which significantly reduces azole levels 2

Monitoring and Follow-up

• Serial Aspergillus antibody titers can help monitor treatment response 1
• Repeat imaging to assess for cavity progression, consolidation, or development of fungus balls 1
• Delays in diagnosis and treatment of chronic necrotizing aspergillosis are associated with worse outcomes 2

Critical Distinction: When to Suspect Contamination

Contamination would be more likely if:

• Only culture was positive WITHOUT positive histopathological staining 1
• Aspergillus was isolated from respiratory secretions or non-sterile sites rather than tissue biopsy 1
• No clinical or radiological findings consistent with fungal infection were present 1
• In your case, none of these apply - you have tissue biopsy with positive staining, making true infection the most likely diagnosis