A Pathology-based Case Series of Influenza- and COVID-19-associated Pulmonary Aspergillosis: The Proof Is in the Tissue

Abstract

Rationale: Invasive pulmonary aspergillosis has emerged as a frequent coinfection in severe coronavirus disease (COVID-19), similarly to influenza, yet the clinical invasiveness is more debated. Objectives: We investigated the invasive nature of pulmonary aspergillosis in histology specimens of influenza and COVID-19 ICU fatalities in a tertiary care center. Methods: In this monocentric, descriptive, retrospective case series, we included adult ICU patients with PCR-proven influenza/COVID-19 respiratory failure who underwent postmortem examination and/or tracheobronchial biopsy during ICU admission from September 2009 until June 2021. Diagnosis of probable/proven viral-associated pulmonary aspergillosis (VAPA) was made based on the Intensive Care Medicine influenza-associated pulmonary aspergillosis and the European Confederation of Medical Mycology (ECMM) and the International Society for Human and Animal Mycology (ISHAM) COVID-19-associated pulmonary aspergillosis consensus criteria. All respiratory tissues were independently reviewed by two experienced pathologists. Measurements and Main Results: In the 44 patients of the autopsy-verified cohort, 6 proven influenza-associated and 6 proven COVID-19-associated pulmonary aspergillosis diagnoses were identified. Fungal disease was identified as a missed diagnosis upon autopsy in 8% of proven cases (n = 1/12), yet it was most frequently found as confirmation of a probable antemortem diagnosis (n = 11/21, 52%) despite receiving antifungal treatment. Bronchoalveolar lavage galactomannan testing showed the highest sensitivity for VAPA diagnosis. Among both viral entities, an impeded fungal growth was the predominant histologic pattern of pulmonary aspergillosis. Fungal tracheobronchitis was histologically indistinguishable in influenza (n = 3) and COVID-19 (n = 3) cases, yet macroscopically more extensive at bronchoscopy in influenza setting. Conclusions: A proven invasive pulmonary aspergillosis diagnosis was found regularly and with a similar histological pattern in influenza and in COVID-19 ICU case fatalities. Our findings highlight an important need for VAPA awareness, with an emphasis on mycological bronchoscopic work-up.

Keywords: COVID-19; critical illness; histology; human influenza; invasive pulmonary aspergillosis.

Figure 1.

Patient flowchart. Flowchart representation of the autopsy and tracheobronchial tissue datasets. COVID-19 = coronavirus disease.

Figure 2.

Viral-associated pulmonary aspergillosis: unimpeded fungal growth pattern. (A–C) Histological images of a patient with influenza-associated pulmonary aspergillosis (IAPA). Histological image derived from left lower lobe, at a magnification of ×8.75; hematoxylin and eosin stain (A) and Grocott-Gomori’s methenamine silver stain (Grocott) (B). Multifocal unimpeded fungal growth within an area of coagulative necrosis is visualized, indicated by black circles and blue box. (C) Magnification of ×50 of the blue-boxed area, showing intrabronchial hyphal growth. (D and E) Lung slide Grocott staining of another patient with IAPA at ×10 (D) and ×50 (E), showing isometric centrifugal growth, invading into a bifurcating artery. PA = pulmonary artery.

Figure 3.

Viral-associated pulmonary aspergillosis: impeded fungal growth pattern. (A and B) Images derived from a case of coronavirus disease (COVID-19)-associated pulmonary aspergillosis, showing acute inflammation of alveolar tissue visualized with hematoxylin and eosin staining (A) and Grocott-Gomori’s methenamine silver (Grocott) staining (B) at ×200 magnification. Dispersed presence of hyphal structures within pneumonia, only apparent upon Grocott stain, is indicated with black box (with magnification). (C and D) Patient with influenza-associated pulmonary aspergillosis, type impeded fungal growth. Grocott staining visualizes bronchopneumonia with fragmented hyphae (black circles/box for magnification), overall low fungal burden, and important neutrophilic infiltration, ×100 magnification.

Figure 4.

Viral-associated invasive Aspergillus tracheobronchitis. Influenza-associated invasive Aspergillus tracheobronchitis: (A) Macroscopic image from bronchoscopy, showing extensive white nodular (red arrows) tracheobronchitis with central ulceration of noduli. (B and C) Microscopic hematoxylin and eosin–stained images at different magnifications, as indicated on the pictures of endobronchial biopsy, showing ulcerated epithelium with neutrophilic debris and acute-angle branching hyphae (black solid arrow) and hyphal invasion into tissue (black dashed arrow). Similar combination of macroscopic (D) and microscopic (E and F) evaluations from a case of coronavirus disease (COVID-19)–associated invasive Aspergillus tracheobronchitis. More extensive macroscopic inflammation visualized in influenza setting, yet comparable microscopic image in influenza and COVID-19 viral background.