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| ==Overview== | | ==Overview== |
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| Influenza illness can include several non-specific symptoms, such as fever, muscle aches, headache, lack of energy, dry cough, sore throat, and possibly runny nose. The fever and body aches can last 3-5 days and the cough and lack of energy may last for 2 or more weeks. | | Influenza illness can include several non-specific symptoms, such as fever, muscle aches, headache, lack of energy, dry cough, sore throat, and possibly runny nose. The fever and body aches can last 3-5 days and the cough and lack of energy may last for 2 or more weeks. The symptoms of the flu are more severe than their common-cold equivalents. |
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| ==History and Symptoms== | | ==History and Symptoms== |
| Symptoms of influenza can start quite suddenly one to two days after infection. Usually symptoms start with chills and fever, which may be as high as 39 °C (103 °F). Patients may need to rest in bed for several days, with aches and pains throughout their bodies, which are worst in their backs and legs.
| | *The typical incubation period for influenza is 1—4 days. |
| | *Adults shed influenza virus from the day before symptoms begin through 5—10 days after illness onset. However, the amount of virus shed, and presumably infectivity, decreases rapidly by 3—5 days after onset in an experimental human infection model. |
| | *Young children also might shed virus several days before illness onset, and children can be infectious for 10 or more days after onset of symptoms. |
| | *Severely immunocompromised persons can shed virus for weeks or months. |
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| Symptoms of influenza may include:
| | *Uncomplicated influenza illness is characterized by the abrupt onset of constitutional and respiratory signs and symptoms, such as fever, myalgia, headache, malaise, nonproductive cough, sore throat, and rhinitis. |
| | *Among children, otitis media, nausea, and vomiting also are commonly reported with influenza illness. Uncomplicated influenza illness typically resolves after 3—7 days for the majority of persons, although cough and malaise can persist for >2 weeks. |
| | *However, influenza virus infections can cause primary influenza viral pneumonia; exacerbate underlying medical conditions (e.g., pulmonary or cardiac disease); lead to secondary bacterial pneumonia, sinusitis, or otitis media; or contribute to coinfections with other viral or bacterial pathogens. |
| | *Young children with influenza virus infection might have initial symptoms mimicking bacterial sepsis with high fevers, and febrile seizures have been reported in 6%—20% of children hospitalized with influenza virus infection. |
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| | ===Common Symptoms=== |
| * Body aches, especially joints and throat | | * Body aches, especially joints and throat |
| * [[Cough]] | | * [[Cough]] |
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| * Reddened eyes, skin (especially face), mouth, throat and nose | | * Reddened eyes, skin (especially face), mouth, throat and nose |
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| It can be difficult to distinguish between the common cold and influenza in the early stages of these infections, but usually the symptoms of the flu are more severe than their common-cold equivalents. Research on signs and symptoms of influenza found that the best findings for excluding the diagnosis of influenza were:<ref name="pmid15728170">{{cite journal | author = Call S, Vollenweider M, Hornung C, Simel D, McKinney W | title = Does this patient have influenza? | journal = JAMA | volume = 293 | issue = 8 | pages = 987-97 | year = 2005 | doi = 10.1001/jama.293.8.987 | id = PMID 15728170}}</ref>
| | ===Less Common Symtoms=== |
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| {| class="wikitable" style="text-align:center"
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| |+ Highest [[sensitivity (tests)|sensitive]] individual findings for diagnosing influenza<ref name="pmid15728170"/>
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| ! Finding: !! [[sensitivity (tests)|sensitivity]] !! [[specificity (tests)|specificity]]
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| |-
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| ! Fever
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| | 86% || 25%
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| |-
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| ! Cough
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| | 98% || 23%
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| |-
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| ! Nasal congestion
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| | 70–90% || 20–40%
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| |-
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| |}
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| Notes to table:
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| * [[Sensitivity (tests)|Sensitivity]] is the proportion of people that tested positive of all the positive people tested.
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| * [[Specificity (tests)|Specificity]] is the proportion of people that tested negative of all the negative people tested.
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| * All three findings, especially fever, were less sensitive in patients over 60 years of age.
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| Since anti-viral drugs are effective in treating influenza if given early (see treatment section, below), it can be important to identify cases early. Of the symptoms listed above, the combinations of findings below can improve diagnostic accuracy.<ref name="pmid11088084">{{cite journal | author = Monto A, Gravenstein S, Elliott M, Colopy M, Schweinle J | title = Clinical signs and symptoms predicting influenza infection. | journal = Arch Intern Med | volume = 160 | issue = 21 | pages = 3243–7 | year = 2000 | url http://archinte.ama-assn.org/cgi/content/abstract/160/21/3243 | id = PMID 11088084}}</ref> Unfortunately, even combinations of findings are imperfect. However, [[Bayes Theorem]] can combine pretest probability with clinical findings to adequately diagnose or exclude influenza in some patients. The pretest probability has a strong seasonal variation; the current prevalence of influenza among patients in the United States receiving sentinel testing is available at the [[Centers for Disease Control and Prevention|CDC]].<ref>Centers for Disease Control and Prevention. [http://www.cdc.gov/flu/weekly/ Weekly Report: Influenza Summary Update.] Accessed January 1, 2007.</ref> Using the CDC data, the following table shows how the likelihood of influenza varies with prevalence:
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| <table border="1" cellpadding="5" class="wikitable">
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| <caption>Combinations of findings for diagnosing influenza<ref name="pmid15728170"/></caption>
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| <tr>
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| <th rowspan="2">Combinations of findings </th>
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| <th rowspan="2">Sensitivity</th>
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| <th rowspan="2">Specificity</th>
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| <th colspan="2"><p>As reported in study<ref name="pmid15728170">.</ref><br/>and projected during local outbreaks<br/>
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| (prevalence= 66%)</p>
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| </th>
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| <th colspan="2">Projected during influenza season <br/>
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| (prevalence=25%)</th>
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| <th colspan="2">Projected in off-season<br/>
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| (prevalence=2%) </th>
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| </tr>
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| <tr>
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| <th>PPV</th>
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| <th>NPV</th>
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| <th>PPV</th>
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| <th>NPV</th>
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| <th>PPV</th>
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| <th>NPV</th>
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| </tr>
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| <tr>
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| <td>Fever and cough</td>
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| <td align="center">64%</td>
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| <td align="center">67%</td>
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| <td align="center">79%</td>
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| <td align="center">49%</td>
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| <td align="center">39%</td>
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| <td align="center">15%</td>
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| <td align="center">4%</td>
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| <td align="center">1%</td>
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| </tr>
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| <tr>
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| <td>Fever and cough and sore throat</td>
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| <td align="center">56</td>
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| <td align="center">71</td>
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| <td align="center">79</td>
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| <td align="center">45</td>
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| <td align="center">39</td>
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| <td align="center">17</td>
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| <td align="center">4</td>
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| <td align="center">2</td>
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| </tr>
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| <tr>
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| <td>Fever and cough and nasal congestion</td>
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| <td align="center">59</td>
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| <td align="center">74</td>
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| <td align="center">81</td>
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| <td align="center">48</td>
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| <td align="center">43</td>
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| <td align="center">16</td>
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| <td align="center">4</td>
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| <td align="center">1</td>
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| </tr>
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| </table>
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| Two [[decision analysis]] studies<ref name="pmif12361816">{{cite journal | author = Smith K, Roberts M | title = Cost-effectiveness of newer treatment strategies for influenza. | journal = Am J Med | volume = 113 | issue = 4 | pages = 300-7 | year = 2002 | doi = 10.1016/S0002-9343(02)01222-6 | id = PMID 12361816}}</ref><ref name="pimd12965940">{{cite journal | author = Rothberg M, Bellantonio S, Rose D | title = Management of influenza in adults older than 65 years of age: cost-effectiveness of rapid testing and antiviral therapy. | journal = Ann Intern Med | volume = 139 | issue = 5 Pt 1 | pages = 321-9 | year = 2003 | url = http://www.annals.org/cgi/content/abstract/139/5_Part_1/321 | id = PMID 12965940}}</ref> suggest that ''during local outbreaks'' of influenza, the prevalence will be over 70%<ref name="pimd12965940"/> and thus patients with any of the above combinations of symptoms may be treated with neuramidase inhibitors without testing. Even in the absence of a local outbreak, treatment may be justified in the elderly during the influenza season as long as the prevalence is over 15%.<ref name="pimd12965940"/>
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| Most people who get influenza will recover in one to two weeks, but others will develop life-threatening complications (such as [[pneumonia]]). According to the [[World Health Organization]]: "Every winter, tens of millions of people get the flu. Most are home, sick and miserable, for about a week. Some—mostly the elderly—die. We know the world-wide death toll exceeds a few hundred thousand people a year, but even in developed countries the numbers are uncertain, because medical authorities don't usually verify who actually died of influenza and who died of a flu-like illness."<ref>Peter M. Sandman and Jody Lanard [http://www.paho.org/English/DD/PIN/Number22_article1a.htm "Bird Flu: Communicating the Risk"] 2005 ''Perspectives in Health Magazine'' Vol. 10 issue 2.</ref> Even healthy people can be affected, and serious problems from influenza can happen at any age. People over 50 years old, very young children and people of any age with chronic medical conditions, are more likely to get complications from influenza: such as pneumonia, [[bronchitis]], [[sinus]], and [[ear infection]]s.<ref name=CDCkeyfacts> [http://www.cdc.gov/flu/protect/keyfacts.htm Key Facts about Influenza (Flu) Vaccine] CDC publication. Published October 17, 2006. Accessed 18 Oct 2006.</ref>
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| The flu can worsen chronic health problems. People with emphysema, chronic bronchitis or asthma may experience shortness of breath while they have the flu, and influenza may cause worsening of [[coronary heart disease]] or [[congestive heart failure]].<ref>Angelo SJ, Marshall PS, Chrissoheris MP, Chaves AM. "Clinical characteristics associated with poor outcome in patients acutely infected with Influenza A." ''Conn Med.'' 2004 Apr;68(4):199–205. PMID 15095826</ref> [[Tobacco smoking|Smoking]] is another [[risk factor]] associated with more serious disease and increased mortality from influenza.<ref>{{cite journal | author = Murin S, Bilello K | title = Respiratory tract infections: another reason not to smoke. | journal = Cleve Clin J Med | volume = 72 | issue = 10 | pages = 916-20 | year = 2005 | id = PMID 16231688}}</ref>
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| ==References== | | ==References== |
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| [[Category:Disease]] | | [[Category:Disease]] |
| [[Category:Mature chapter]]
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| [[Category:Pulmonology]] | | [[Category:Pulmonology]] |
| [[Category:Influenza| ]] | | [[Category:Influenza| ]] |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Alejandro Lemor, M.D. [2]
Overview
Influenza illness can include several non-specific symptoms, such as fever, muscle aches, headache, lack of energy, dry cough, sore throat, and possibly runny nose. The fever and body aches can last 3-5 days and the cough and lack of energy may last for 2 or more weeks. The symptoms of the flu are more severe than their common-cold equivalents.
History and Symptoms
- The typical incubation period for influenza is 1—4 days.
- Adults shed influenza virus from the day before symptoms begin through 5—10 days after illness onset. However, the amount of virus shed, and presumably infectivity, decreases rapidly by 3—5 days after onset in an experimental human infection model.
- Young children also might shed virus several days before illness onset, and children can be infectious for 10 or more days after onset of symptoms.
- Severely immunocompromised persons can shed virus for weeks or months.
- Uncomplicated influenza illness is characterized by the abrupt onset of constitutional and respiratory signs and symptoms, such as fever, myalgia, headache, malaise, nonproductive cough, sore throat, and rhinitis.
- Among children, otitis media, nausea, and vomiting also are commonly reported with influenza illness. Uncomplicated influenza illness typically resolves after 3—7 days for the majority of persons, although cough and malaise can persist for >2 weeks.
- However, influenza virus infections can cause primary influenza viral pneumonia; exacerbate underlying medical conditions (e.g., pulmonary or cardiac disease); lead to secondary bacterial pneumonia, sinusitis, or otitis media; or contribute to coinfections with other viral or bacterial pathogens.
- Young children with influenza virus infection might have initial symptoms mimicking bacterial sepsis with high fevers, and febrile seizures have been reported in 6%—20% of children hospitalized with influenza virus infection.
Common Symptoms
Less Common Symtoms
References
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