IAPA has emerged as a severe complication of influenza, especially in ICU patients, and this secondary infection may occur in any patient, including those considered to be at low risk of developing IPA. The global epidemiology of IAPA may be variable, which might be partly due to underdiagnosis [24]. The clinical presentation of IAPA includes invasive Aspergillus tracheobronchitis, which requires bronchoscopic visualization of plaques in the airways to make a diagnosis. Aspergillus culture and BAL GM are positive in > 80% of IAPA cases, and ordering such tests is recommended in influenza cases in the ICU. The proposed case definition relies on an entry criterion based on an influenza-like illness and the detection of influenza virus. The case definition distinguishes between invasive tracheobronchitis and other pulmonary forms of IAPA, with demonstration of invasive fungal hyphae with positive mycology qualifying as proven infection. Detection of GM or positive Aspergillus culture in BAL is the main mycological criteria in probable case definition.