Influenza differential diagnosis

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For more information about non-human (variant) influenza viruses that may be transmitted to humans, see Zoonotic influenza

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Associate Editor(s)-in-Chief: Alejandro Lemor, M.D. [2]

Overview

Influenza should be differentiated from other conditions that cause fever, cough, myalgias, headache and fatigue, such as RSV infection, dengue fever, parainfluenza virus infection, ebola infection adenovirus infection, rhinovirus infection, and legionella infection.

Differential Diagnosis

Influenza should be differentiated from the following diseases or pathogens that cause upper or lower respiratory disease or flu-like symptoms:

Infectious Diseases

• Other influenza viruses, such as human influenza or swine influenza are in the differential diagnosis of avian influenza.
• Other infectious agents, including viruses, bacteria, fungi, and parasites, that are typically responsible for respiratory illness are also in the differential diagnosis of avian influenza:
  • Adenoviruses
  • Anthrax (caused by B. anthracis)
  • Arenaviruses
  • Cytomegalovirus (CMV)
  • Chlamydia pneumoniae
  • Coronaviruses (responsible for SARS and MERS)
  • Dengue fever
  • Echoviruses
  • Ebola virus infection
  • Hantavirus pulmonary syndrome
  • Herpes viruses
  • HIV disease
  • Histoplasmosis and other fungal causes of respiratory disease
  • Human metapneumovirus
  • Malaria
  • Measles
  • Parainfluenza virus
  • Poliovirus infection
  • Q fever
  • Rhinovirus
  • Respiratory syncytial virus
  • Other bacterial causes of nasopharyngeal and respiratory infection, such as S. pneumoniae, S. aureus, H. influenzae, M. pneumoniae, M. tuberculosis, L. pneumophila.

Non-infectious Diseases

• Asthma
• Bronchiectasis
• Chronic obstructive pulmonary disease and emphysema
• Drugs, such as interferons, monoclonal antibodies, bisphosphonates, and chemotherapeutic agents
• Hematologic malignancies (leukemias and lymphomas)
• Myocarditis
• Metal fume fever
• Pericarditis
• Pulmonary embolism
• Vaccinations (typically transient and mild flu-like illness)

Differentiating Flu and Common Cold

Symptoms	Flu	Common Cold
Fever	High fever (100-102° F)	Rare
Headache	Common	Rare
Cough	Common, moderate to severe	Mild to moderate
Body aches	Common, may be severe	Slight
Fatigue	Usual, can last up to 2-3 weeks	Sometimes
Nasal congestion	Sometimes	Common
Sneezing	Sometimes	Common
Sore throat	Sometimes	Common
Adapted from the National Institute of Allergy and Infectious Diseases (NIAID)

Disease	Clinical Manifestations							Lab findings			Imaging findings	Main treatment
	Cough	Sputum	Dyspnea	Sore throat	Headache	Confusion	Diarrhea	Hyponatremia	Leukopenia	Abnormal Liver function tests
Influenza	++	++	++	++	++	+/-	+/-	-	-	-	Bi-basal air-space opacities Perihilar reticular and alveolar infiltrates	Zanamivir, oseltamivir
Psittacosis	++	-	+	-	+++	+	Minimal	-	+	-	No changes seen	Doxycycline
C.pneumoniae pneumonia	+	+	+	+++	++	+	-	-	-	-	Minimal changes observed	Doxycycline, azithromycin
M. pneumoniae pneumonia	++	++	++	-	-	-	-	-	-	+	Bronchial wall thickening Centrilobular nodules Ground-glass attenuation Consolidation	Doxycycline
L. pneumophila infection	+	+++	+++	-	+	++	+	++	+	++	Often multifocal	Doxycycline
Endocarditis	++	++	+	-	-	-	-	-	+/-	+/-	Hazy opacities at lung bases bilaterally	Vancomycin
Coxiella burnetii infection	++	-	+	+/-	-	+/-	Minimal	-	+/-	+/-	Segmental or lobar opacification Occasional pleural effusions	Doxycycline
Leptospirosis	++	+	++	+	+	++	-	+++			Multiple ill-defined nodules in both lungs.	Doxycycline, azithromycin, amoxicillin
Brucellosis	++	-	+	-	++	+	-	+/-	+/-	+/-	Soft miliary mottling Parenchymal nodules Consolidation Chronic diffuse changes Hilar or paratracheal lymphadenopathy Pneumothorax	Doxycycline, rifampin

Key;

+: Occurs in some cases

++: Occurs in many cases

+++: Occurs frequently