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Influenza

Signs and Symptoms of the Flu

Influenza, commonly called the “flu”, is a respiratory infection that is different from the “common cold” or the “stomach flu” (NIAID 2011). Influenza is primarily characterized by inflammation of tissues that line the nasal cavity, throat, the inner surface of the eyelids (ie, conjunctiva), and the lungs (NIH 2012a; Kim 2011; Sanders 2011; Snelgrove 2011). Common clinical symptoms of influenza include a sudden onset of fever, fatigue, headache, and muscle aches (Shobugawa 2012). Although both the flu and the common cold are caused by a viral infection of the respiratory system, symptoms of the common cold rarely include severe fever, headaches, or extreme exhaustion (NIAID 2011). More information is available in the Common Cold protocol.

Common Cold vs. The Flu: Comparison of Characteristics

Feature

Colds

Flu

Etiological Agent

>200 viral strains; rhinovirus most common

3 strains of influenza virus: influenza A, B, and C

Site of Infection

Upper respiratory tract

Entire respiratory system

Symptom Onset

Gradual: 1-3 days

Sudden: within a few hours

Fever, chills

Occasional, low grade (<101° F)

Characteristic, higher (>101° F),
lasting 2-4 days

Headache

Infrequent, usually mild

Characteristic, more severe

General aches, pains

Mild, if any

Characteristic, often severe and affecting the entire body

Sore throat

Common, usually mild

Sometimes present

Cough, chest congestion

Common; mild-to-moderate, with hacking, productive cough

Common; potentially severe dry, non-productive cough

Runny, stuffy nose

Very common, accompanied by bouts of sneezing

Sometimes present

Fatigue, weakness

Mild, if any

Usual, may be severe and last 2-3 weeks

Extreme exhaustion

Rarely

Frequent, usually in early stages of illness

Season

Year around, peaks in winter months

Most cases between November and February

Antibiotics helpful?

No, unless secondary bacterial infection develops

No, unless secondary bacterial infection develops

(Roxas 2007; MD Consult 2012; Utah Dept. Health 2010; CDC 2011e; Oklahoma State Dept. of Health 2011)