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

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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

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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

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* 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

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* 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

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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 | ++  | ++  | ++  | ++  | ++  | +/-  | +/-  | \-  | \-  | \-  |

* 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

## References

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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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