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]


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:[1][2]

Infectious Diseases

Non-infectious Diseases

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) [3]
Disease Clinical Manifestations Lab findings Imaging findings Main treatment
Cough Sputum Dyspnea Sore throat Headache Confusion Diarrhea Hyponatremia Leukopenia Abnormal Liver function tests
Influenza ++ ++ ++ ++ ++ +/- +/- - - - Zanamivir, oseltamivir
Psittacosis ++ - + - +++ + Minimal - + -
  • No changes seen
C.pneumoniae pneumonia + + + +++ ++ + - - - -
  • Minimal changes observed
Doxycycline, azithromycin
M. pneumoniae pneumonia ++ ++ ++ - - - - - - + Doxycycline
L. pneumophila infection + +++ +++ - + ++ + ++ + ++
  • Often multifocal
Endocarditis ++ ++ + - - - - - +/- +/-
  • Hazy opacities at lung bases bilaterally
Coxiella burnetii infection ++ - + +/- - +/- Minimal - +/- +/- Doxycycline
Leptospirosis ++ + ++ + + ++ - +++
  • Multiple ill-defined nodules in both lungs.
Doxycycline, azithromycin, amoxicillin
Brucellosis ++ - + - ++ + - +/- +/- +/- Doxycycline, rifampin


+: Occurs in some cases

++: Occurs in many cases

+++: Occurs frequently


  1. Szewczuk, Elektra; Thapa, Kiran; Anninos, Terry; McPhie, Kenneth; Higgins, Geoff; Dwyer, Dominic E; Stanley, Keith K; Iredell, Jonathan R (2010). "Rapid semi-automated quantitative multiplex tandem PCR (MT-PCR) assays for the differential diagnosis of influenza-like illness". BMC Infectious Diseases. 10 (1): 113. doi:10.1186/1471-2334-10-113. ISSN 1471-2334.
  2. Liu, Ding Xiang; Schulze, Martin; Nitsche, Andreas; Schweiger, Brunhilde; Biere, Barbara (2010). "Diagnostic Approach for the Differentiation of the Pandemic Influenza A(H1N1)v Virus from Recent Human Influenza Viruses by Real-Time PCR". PLoS ONE. 5 (4): e9966. doi:10.1371/journal.pone.0009966. ISSN 1932-6203.
  3. "National Institute of Allergy and Infectious Diseases (NIAID)- Flu (Influenza)".

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