Table 3.

Differential diagnoses of several types of pneumonia in patients with HMs

Characteristics	Viral pneumonia						Fungal pneumonia	Drug-induced pneumonia
	COVID-19	Adenovirus pneumonia	CMV pneumonia	RSV pneumonia	Influenza virus pneumonia	HPIV pneumonia
Causative factor	SARS-CoV-2	Adenovirus	CMV	RSV	Influenza virus	HPIV	Pneumocystis jirovecii	Medicine (e.g., MTX, RTX)
Epidemiology	Travel history to an area with high prevalence or contact history with infected patients	Year-round	Mostly after allo-HCT	Seasonal variation of incidence	Seasonal variation of incidence	Year-round	Common in immunodeficiency patients
Symptoms and signs	Common symptoms: onset with symptoms of upper respiratory infection, such as fever, headache, sore throat, and nasal congestion. When it progresses to pneumonia, most develop a non-productive cough with persistent high fever, dyspnea, etc. Their manifestations vary from asymptomatic patterns to end-organ damage, such as ARDS.						Fever, non-productive cough, dyspnea, etc.	Dyspnea, fever, cough
	Common signs: diminished breath sounds with wheezing rales or crackles.
Laboratory findings	Most viral infection induces a reduction of leukocytes and lymphocytes, whereas a routine blood test is not always reliable and typical.						Special staining of the sample from BAL
	Combination of viral nucleic acid detection and antibody detection could differentiate various infections.
CT imaging	Diffuse bilateral ground-glass infiltrates small multifocal nodules, bronchial vascular thickening, and/or airspace consolidation.						Bilateral, patchy GGOs, and cystic lesions	Diffuse interstitial infiltrates
Distribution of lesions	Peripheral	Multifocal	Diffuse	Airway, multifocal	Airway, multifocal	Airway, multifocal
GGO	+#	+++	++++	+	+	+	Common (not as common as in patients without HMs)	Common
Consolidation	Uncommon	+++	++	+	+	+	Uncommon
Nodule	Rare	Centrilobular+	++	Centrilobular+++	++	Centrilobular++	Uncommon
Pleural effusion	Uncommon	Common	Rare	Common	Uncommon	Uncommon	Rare
References	Koo et al., 2018; Fontana and Strasfeld, 2019						Cordonnier et al., 2017	Atzeni et al., 2013

^# Involvement of lung was graded by “+/++/+++/++++”: +, 10%–<25%; ++, 25%–<50%; +++, 50%–<75%; ++++, no less than 75%. Allo-HCT, allogeneic hematopoietic cell transplantation; ARDS, acute respiratory distress syndrome; BAL, bronchoalveolar lavage; CMV, cytomegalovirus; GGO, ground-glass opacity; HMs, hematological malignancies; HPIV, human parainfluenza virus; MTX, methotrexate; RSV, respiratory syncytial virus; RTX, rituximab; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2