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Latest revision as of 22:24, 29 July 2020

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 illness can include several non-specific symptoms, such as fever, muscle aches, headache, lack of energy, dry cough, sore throat, and 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.

Influenza-like illness (ILI) t is defined as 'a fever (temperature ≥100.0°F [≥37.8°C], oral or equivalent) and cough and/or sore throat, without a known cause other than influenza."^[1]

History and Symptoms Adapted from CDC^[2]

The typical incubation period for influenza is 1-4 days.
Adults shed influenza virus from the day before symptoms manifest through 5-10 days after their 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 such as 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.

Image courtesy of Häggström, Mikael. "Medical gallery of Mikael Häggström 2014". Wikiversity Journal of Medicine 1^[3]

Common Symptoms

Fever (seen in the majority of patients)
Cough (seen in the majority of patients)
Chills
Dizziness
Flushed face
Myalgia
Sneezing
Rhinorrhea
Fatigue
Headache
Conjunctivitis
Nasal congestion
Sore throat

Less Common Symptoms

Nausea
Vomiting
Diarrhea
Reddened eyes, skin (especially face), mouth, throat and nose
Shortness of breath (especially in asthmatic patients)^[4]
Loss of appetite
Sweating
Muscle stiffness
Hemoptysis^[4]

History and physical examination

Since anti-viral drugs are effective in treating influenza if given early (see treatment section, below), it can be important to identify cases early. A systematic review by the Rational Clinical Examination concluded that the best findings for excluding the diagnosis of influenza are:^[5]

Most sensitive individual findings for diagnosing influenza^[5]
Finding:	Sensitivity	Specificity
Fever†	86%†	25%
Cough†	98%†	23%
Sore throat	~80%†	~30%
Nasal congestion†	70–90%†	20–40%
Headache†	70–90%†	20–40%
Myalgia†	60-90%†	~30%
Absence of vaccination	83-97%	14-19%^[6]^[7]
Note: † These findings, especially fever, were less sensitive in patients over 60 years of age.^[5]

Using the symptoms listed above, the combinations of findings below can improve diagnostic accuracy.^[8] Unfortunately, even combinations of findings are imperfect. Studies of combining symptoms have included use of recursive partitioning; however, this study combined two cohorts with different prevalences of influenza.^[9] 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 CDC.^[10] Using the CDC data, the following table shows how the likelihood of influenza varies with prevalence:

Combinations of findings for diagnosing influenza^[11]^[12]^[5]
Combinations of findings	Sensitivity	Specificity	Projected during local outbreaks (prevalence approx 66%^[13]^[14])		Projected during influenza season (prevalence=25%)		Projected in off-season (prevalence=2%)
Combinations of findings	Sensitivity	Specificity	PPV	NPV	PPV	NPV	PPV	NPV
Fever and cough	64% 61%^[12]	67% 80%^[12]	79% 86%^[12]	51% 51%^[12]	39% 50%^[12]	85% 86%^[12]	4% 6%^[12]	99% 99%^[12]
Fever and cough and sore throat	56	71	79	45	39	83	4	98
Fever and cough and nasal congestion	59	74	81	48	43	84	4	99
Fever and cough and acute onset^[12]	41	93	92	55	66	83	11	99
A score of 3 or more from: • New or increased cough (2 points) • Headache (1 point) • Subjective fever (1 point) • Triage temperature >100.4°C (1 point)^[11]	92	35	73	69	32	93	3	> 99

Clinical Prediction Rule

Per the bottom row of the table above, a score of 3 or more from^[11]:

New or increased cough (2 points)
Headache (1 point)
Subjective fever (1 point)
Triage temperature >100.4°C (1 point)

References

↑ Blanton L, Alabi N, Mustaquim D, Taylor C, Kniss K, Kramer N; et al. (2017). "Update: Influenza Activity in the United States During the 2016-17 Season and Composition of the 2017-18 Influenza Vaccine". MMWR Morb Mortal Wkly Rep. 66 (25): 668–676. doi:10.15585/mmwr.mm6625a3. PMID 28662019.
↑ "CDC Clinical Signs and Symptoms of Influenza".
↑ Häggström, Mikael (2014). "Medical gallery of Mikael Häggström 2014". Wikiversity Journal of Medicine. 1 (2). doi:10.15347/wjm/2014.008. ISSN 2001-8762.
↑ ^4.0 ^4.1 Gao, Hai-Nv; Lu, Hong-Zhou; Cao, Bin; Du, Bin; Shang, Hong; Gan, Jian-He; Lu, Shui-Hua; Yang, Yi-Da; Fang, Qiang; Shen, Yin-Zhong; Xi, Xiu-Ming; Gu, Qin; Zhou, Xian-Mei; Qu, Hong-Ping; Yan, Zheng; Li, Fang-Ming; Zhao, Wei; Gao, Zhan-Cheng; Wang, Guang-Fa; Ruan, Ling-Xiang; Wang, Wei-Hong; Ye, Jun; Cao, Hui-Fang; Li, Xing-Wang; Zhang, Wen-Hong; Fang, Xu-Chen; He, Jian; Liang, Wei-Feng; Xie, Juan; Zeng, Mei; Wu, Xian-Zheng; Li, Jun; Xia, Qi; Jin, Zhao-Chen; Chen, Qi; Tang, Chao; Zhang, Zhi-Yong; Hou, Bao-Min; Feng, Zhi-Xian; Sheng, Ji-Fang; Zhong, Nan-Shan; Li, Lan-Juan (2013). "Clinical Findings in 111 Cases of Influenza A (H7N9) Virus Infection". New England Journal of Medicine. 368 (24): 2277–2285. doi:10.1056/NEJMoa1305584. ISSN 0028-4793.
↑ ^5.0 ^5.1 ^5.2 ^5.3 Call SA, Vollenweider MA, Hornung CA, Simel DL, McKinney WP (2005). "Does this patient have influenza?". JAMA. 293 (8): 987–97. doi:10.1001/jama.293.8.987. PMID 15728170. Review in: Evid Based Nurs. 2005 Oct;8(4):121
↑ Hulson TD, Mold JW, Scheid D; et al. (2001). "Diagnosing influenza: the value of clinical clues and laboratory tests". J Fam Pract. 50 (12): 1051–6. PMID 11742606.
↑ van Elden LJ, van Essen GA, Boucher CA; et al. (2001). "Clinical diagnosis of influenza virus infection: evaluation of diagnostic tools in general practice". Br J Gen Pract. 51 (469): 630–4. PMC 1314072. PMID 11510391.
↑ Monto A, Gravenstein S, Elliott M, Colopy M, Schweinle J (2000). "Clinical signs and symptoms predicting influenza infection". Arch Intern Med. 160 (21): 3243–7. PMID 11088084.
↑ Afonso AM, Ebell MH, Gonzales R, Stein J, Genton B, Senn N (2012). "The use of classification and regression trees to predict the likelihood of seasonal influenza". Fam Pract. doi:10.1093/fampra/cms020. PMID 22427440.
↑ Centers for Disease Control and Prevention. Weekly Report: Influenza Summary Update. Accessed January 1, 2007.
↑ ^11.0 ^11.1 ^11.2 Dugas AF, Hsieh YH, Lovecchio F, Moran GJ, Steele MT, Talan DA; et al. (2019). "Derivation and Validation of a Clinical Decision Guideline for Influenza Testing in Four U.S. Emergency Departments". Clin Infect Dis. doi:10.1093/cid/ciz171. PMID 30843056.
↑ ^12.00 ^12.01 ^12.02 ^12.03 ^12.04 ^12.05 ^12.06 ^12.07 ^12.08 ^12.09 Ebell MH, Afonso AM, Gonzales R, Stein J, Genton B, Senn N (2012). "Development and validation of a clinical decision rule for the diagnosis of influenza". J Am Board Fam Med. 25 (1): 55–62. doi:10.3122/jabfm.2012.01.110161. PMID 22218625.
↑ Smith K, Roberts M (2002). "Cost-effectiveness of newer treatment strategies for influenza". Am J Med. 113 (4): 300–7. doi:10.1016/S0002-9343(02)01222-6. PMID 12361816.
↑ Rothberg M, Bellantonio S, Rose D (2003). "Management of influenza in adults older than 65 years of age: cost-effectiveness of rapid testing and antiviral therapy". Ann Intern Med. 139 (5 Pt 1): 321–9. PMID 12965940.

Template:WH Template:WS

[pmid28662019-1] Blanton L, Alabi N, Mustaquim D, Taylor C, Kniss K, Kramer N; et al. (2017). "Update: Influenza Activity in the United States During the 2016-17 Season and Composition of the 2017-18 Influenza Vaccine". MMWR Morb Mortal Wkly Rep. 66 (25): 668–676. doi:10.15585/mmwr.mm6625a3. PMID 28662019.

[2] "CDC Clinical Signs and Symptoms of Influenza".

[Häggström2014-3] Häggström, Mikael (2014). "Medical gallery of Mikael Häggström 2014". Wikiversity Journal of Medicine. 1 (2). doi:10.15347/wjm/2014.008. ISSN 2001-8762.

[GaoLu2013-4] 4.0 ^4.1 Gao, Hai-Nv; Lu, Hong-Zhou; Cao, Bin; Du, Bin; Shang, Hong; Gan, Jian-He; Lu, Shui-Hua; Yang, Yi-Da; Fang, Qiang; Shen, Yin-Zhong; Xi, Xiu-Ming; Gu, Qin; Zhou, Xian-Mei; Qu, Hong-Ping; Yan, Zheng; Li, Fang-Ming; Zhao, Wei; Gao, Zhan-Cheng; Wang, Guang-Fa; Ruan, Ling-Xiang; Wang, Wei-Hong; Ye, Jun; Cao, Hui-Fang; Li, Xing-Wang; Zhang, Wen-Hong; Fang, Xu-Chen; He, Jian; Liang, Wei-Feng; Xie, Juan; Zeng, Mei; Wu, Xian-Zheng; Li, Jun; Xia, Qi; Jin, Zhao-Chen; Chen, Qi; Tang, Chao; Zhang, Zhi-Yong; Hou, Bao-Min; Feng, Zhi-Xian; Sheng, Ji-Fang; Zhong, Nan-Shan; Li, Lan-Juan (2013). "Clinical Findings in 111 Cases of Influenza A (H7N9) Virus Infection". New England Journal of Medicine. 368 (24): 2277–2285. doi:10.1056/NEJMoa1305584. ISSN 0028-4793.

[pmid15728170-5] 5.0 ^5.1 ^5.2 ^5.3 Call SA, Vollenweider MA, Hornung CA, Simel DL, McKinney WP (2005). "Does this patient have influenza?". JAMA. 293 (8): 987–97. doi:10.1001/jama.293.8.987. PMID 15728170. Review in: Evid Based Nurs. 2005 Oct;8(4):121

[pmid11742606-6] Hulson TD, Mold JW, Scheid D; et al. (2001). "Diagnosing influenza: the value of clinical clues and laboratory tests". J Fam Pract. 50 (12): 1051–6. PMID 11742606.

[pmid11510391-7] van Elden LJ, van Essen GA, Boucher CA; et al. (2001). "Clinical diagnosis of influenza virus infection: evaluation of diagnostic tools in general practice". Br J Gen Pract. 51 (469): 630–4. PMC 1314072. PMID 11510391.

[pmid11088084-8] Monto A, Gravenstein S, Elliott M, Colopy M, Schweinle J (2000). "Clinical signs and symptoms predicting influenza infection". Arch Intern Med. 160 (21): 3243–7. PMID 11088084.

[pmid22427440-9] Afonso AM, Ebell MH, Gonzales R, Stein J, Genton B, Senn N (2012). "The use of classification and regression trees to predict the likelihood of seasonal influenza". Fam Pract. doi:10.1093/fampra/cms020. PMID 22427440.

[10] Centers for Disease Control and Prevention. Weekly Report: Influenza Summary Update. Accessed January 1, 2007.

[pmid30843056-11] 11.0 ^11.1 ^11.2 Dugas AF, Hsieh YH, Lovecchio F, Moran GJ, Steele MT, Talan DA; et al. (2019). "Derivation and Validation of a Clinical Decision Guideline for Influenza Testing in Four U.S. Emergency Departments". Clin Infect Dis. doi:10.1093/cid/ciz171. PMID 30843056.

[pmid22218625-12] 12.00 ^12.01 ^12.02 ^12.03 ^12.04 ^12.05 ^12.06 ^12.07 ^12.08 ^12.09 Ebell MH, Afonso AM, Gonzales R, Stein J, Genton B, Senn N (2012). "Development and validation of a clinical decision rule for the diagnosis of influenza". J Am Board Fam Med. 25 (1): 55–62. doi:10.3122/jabfm.2012.01.110161. PMID 22218625.

[pmif12361816-13] Smith K, Roberts M (2002). "Cost-effectiveness of newer treatment strategies for influenza". Am J Med. 113 (4): 300–7. doi:10.1016/S0002-9343(02)01222-6. PMID 12361816.

[pimd12965940-14] Rothberg M, Bellantonio S, Rose D (2003). "Management of influenza in adults older than 65 years of age: cost-effectiveness of rapid testing and antiviral therapy". Ann Intern Med. 139 (5 Pt 1): 321–9. PMID 12965940.

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@@ Line 1: / Line 1: @@
 __NOTOC__
 {{Influenza}}
+'''For more information about non-human (variant) influenza viruses that may be transmitted to humans, see [[Zoonotic influenza]]'''<br><br>
 {{CMG}}; {{AE}} {{AL}}
 ==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.
+Influenza illness can include several non-specific symptoms, such as [[fever]], [[muscle aches]], [[headache]], lack of energy, [[dry cough]], [[sore throat]], and [[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==
+Influenza-like illness (ILI) t is defined as 'a fever (temperature ≥100.0°F [≥37.8°C], oral or equivalent) and cough and/or sore throat, without a known cause other than influenza."<ref name="pmid28662019">{{cite journal| author=Blanton L, Alabi N, Mustaquim D, Taylor C, Kniss K, Kramer N et al.| title=Update: Influenza Activity in the United States During the 2016-17 Season and Composition of the 2017-18 Influenza Vaccine. | journal=MMWR Morb Mortal Wkly Rep | year= 2017 | volume= 66 | issue= 25 | pages= 668-676 | pmid=28662019 | doi=10.15585/mmwr.mm6625a3 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=28662019  }} </ref>
-*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.
+==History and Symptoms  <small><small><small><small>Adapted from CDC<ref>{{cite web| url=http://www.cdc.gov/flu/professionals/acip/clinical.htm| title=CDC Clinical Signs and Symptoms of Influenza}} </ref></small></small></small></small>==
+*The typical incubation period for influenza is 1-4 days.
+*Adults shed influenza virus from the day before symptoms manifest through 5-10 days after their 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 such as 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.
-*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.
+{|style="float:right"
-*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.
+|[[File:Symptoms of influenza.png|thumb|400px|Image courtesy of  Häggström, Mikael. "Medical gallery of Mikael Häggström 2014". Wikiversity Journal of Medicine 1<ref name="Häggström2014">{{cite journal|last1=Häggström|first1=Mikael|title=Medical gallery of Mikael Häggström 2014|journal=Wikiversity Journal of Medicine|volume=1|issue=2|year=2014|issn=20018762|doi=10.15347/wjm/2014.008}}</ref>]]
-*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===
-* Body aches, especially joints and throat
+*[[Fever]] (seen in the majority of patients)
-* [[Cough]]
+*[[Cough]] (seen in the majority of patients)
+*[[Chills]]
+*[[Dizziness]]
+*Flushed [[face]]
+*Myalgia
 *[[sneeze|Sneezing]]
-* Extreme coldness
+*Rhinorrhea
-*[[Fever]]
 *[[Fatigue]]
 *[[Headache]]
-*Irritated watering eyes
+*Conjunctivitis
 * [[Nasal congestion]]
-* [[Nausea]] and [[vomiting]]
+*[[Sore throat]]
+===Less Common Symptoms===
+* [[Nausea]]
+* [[Vomiting]]
+* [[Diarrhea]]
 * Reddened eyes, skin (especially face), mouth, throat and nose
+* [[Shortness of breath]] (especially in asthmatic patients)<ref name="GaoLu2013">{{cite journal|last1=Gao|first1=Hai-Nv|last2=Lu|first2=Hong-Zhou|last3=Cao|first3=Bin|last4=Du|first4=Bin|last5=Shang|first5=Hong|last6=Gan|first6=Jian-He|last7=Lu|first7=Shui-Hua|last8=Yang|first8=Yi-Da|last9=Fang|first9=Qiang|last10=Shen|first10=Yin-Zhong|last11=Xi|first11=Xiu-Ming|last12=Gu|first12=Qin|last13=Zhou|first13=Xian-Mei|last14=Qu|first14=Hong-Ping|last15=Yan|first15=Zheng|last16=Li|first16=Fang-Ming|last17=Zhao|first17=Wei|last18=Gao|first18=Zhan-Cheng|last19=Wang|first19=Guang-Fa|last20=Ruan|first20=Ling-Xiang|last21=Wang|first21=Wei-Hong|last22=Ye|first22=Jun|last23=Cao|first23=Hui-Fang|last24=Li|first24=Xing-Wang|last25=Zhang|first25=Wen-Hong|last26=Fang|first26=Xu-Chen|last27=He|first27=Jian|last28=Liang|first28=Wei-Feng|last29=Xie|first29=Juan|last30=Zeng|first30=Mei|last31=Wu|first31=Xian-Zheng|last32=Li|first32=Jun|last33=Xia|first33=Qi|last34=Jin|first34=Zhao-Chen|last35=Chen|first35=Qi|last36=Tang|first36=Chao|last37=Zhang|first37=Zhi-Yong|last38=Hou|first38=Bao-Min|last39=Feng|first39=Zhi-Xian|last40=Sheng|first40=Ji-Fang|last41=Zhong|first41=Nan-Shan|last42=Li|first42=Lan-Juan|title=Clinical Findings in 111 Cases of Influenza A (H7N9) Virus Infection|journal=New England Journal of Medicine|volume=368|issue=24|year=2013|pages=2277–2285|issn=0028-4793|doi=10.1056/NEJMoa1305584}}</ref>
+*[[Loss of appetite]]
+*[[Sweating]]
+*Muscle stiffness
+*[[Hemoptysis]]<ref name="GaoLu2013">{{cite journal|last1=Gao|first1=Hai-Nv|last2=Lu|first2=Hong-Zhou|last3=Cao|first3=Bin|last4=Du|first4=Bin|last5=Shang|first5=Hong|last6=Gan|first6=Jian-He|last7=Lu|first7=Shui-Hua|last8=Yang|first8=Yi-Da|last9=Fang|first9=Qiang|last10=Shen|first10=Yin-Zhong|last11=Xi|first11=Xiu-Ming|last12=Gu|first12=Qin|last13=Zhou|first13=Xian-Mei|last14=Qu|first14=Hong-Ping|last15=Yan|first15=Zheng|last16=Li|first16=Fang-Ming|last17=Zhao|first17=Wei|last18=Gao|first18=Zhan-Cheng|last19=Wang|first19=Guang-Fa|last20=Ruan|first20=Ling-Xiang|last21=Wang|first21=Wei-Hong|last22=Ye|first22=Jun|last23=Cao|first23=Hui-Fang|last24=Li|first24=Xing-Wang|last25=Zhang|first25=Wen-Hong|last26=Fang|first26=Xu-Chen|last27=He|first27=Jian|last28=Liang|first28=Wei-Feng|last29=Xie|first29=Juan|last30=Zeng|first30=Mei|last31=Wu|first31=Xian-Zheng|last32=Li|first32=Jun|last33=Xia|first33=Qi|last34=Jin|first34=Zhao-Chen|last35=Chen|first35=Qi|last36=Tang|first36=Chao|last37=Zhang|first37=Zhi-Yong|last38=Hou|first38=Bao-Min|last39=Feng|first39=Zhi-Xian|last40=Sheng|first40=Ji-Fang|last41=Zhong|first41=Nan-Shan|last42=Li|first42=Lan-Juan|title=Clinical Findings in 111 Cases of Influenza A (H7N9) Virus Infection|journal=New England Journal of Medicine|volume=368|issue=24|year=2013|pages=2277–2285|issn=0028-4793|doi=10.1056/NEJMoa1305584}}</ref>
+===History and physical examination===
+Since anti-viral drugs are effective in treating influenza if given early (see treatment section, below), it can be important to identify cases early. A [[systematic review]] by the [http://jama.ama-assn.org/cgi/collection/rational_clinical_exam Rational Clinical Examination] concluded that the best findings for excluding the diagnosis of influenza are:<ref name="pmid15728170">{{cite journal| author=Call SA, Vollenweider MA, Hornung CA, Simel DL, McKinney WP| title=Does this patient have influenza? | journal=JAMA | year= 2005 | volume= 293 | issue= 8 | pages= 987-97 | pmid=15728170
+| url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=15728170 | doi=10.1001/jama.293.8.987 }}  [http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=16247902 Review in: Evid Based Nurs. 2005 Oct;8(4):121]</ref>
-===Less Common Symtoms===
+{| class="wikitable"
+|+ Most [[sensitivity (tests)|sensitive]] individual findings for diagnosing influenza<ref name="pmid15728170"/>
+! style="text-align:center"|Finding: !! [[sensitivity (tests)|Sensitivity]] !! [[specificity (tests)|Specificity]]
+|-
+! Fever†
+| style="text-align:center"|86%† ||style="text-align:center"| 25%
+|-
+! Cough†
+| style="text-align:center"|98%† ||style="text-align:center"| 23%
+|-
+! Sore throat
+| style="text-align:center"|~80%† ||style="text-align:center"| ~30%
+|-
+! Nasal congestion†
+| style="text-align:center"|70–90%† || style="text-align:center"|20–40%
+|-
+! Headache†
+| style="text-align:center"|70–90%† || style="text-align:center"|20–40%
+|-
+! Myalgia†
+| style="text-align:center"|60-90%† ||style="text-align:center"| ~30%
+|-
+! Absence of vaccination
+| style="text-align:center"|83-97% || style="text-align:center"|14-19%<ref name="pmid11742606">{{cite journal |author=Hulson TD, Mold JW, Scheid D, ''et al'' |title=Diagnosing influenza: the value of clinical clues and laboratory tests |journal=J Fam Pract |volume=50 |issue=12 |pages=1051–6 |year=2001 |pmid=11742606 |doi= |url=http://www.jfponline.com/Pages.asp?AID=2406 |issn=}}</ref><ref name="pmid11510391">{{cite journal |author=van Elden LJ, van Essen GA, Boucher CA, ''et al'' |title=Clinical diagnosis of influenza virus infection: evaluation of diagnostic tools in general practice |journal=Br J Gen Pract |volume=51 |issue=469 |pages=630–4 |year=2001 |pmid=11510391 |pmc=1314072 |doi= |url=http://openurl.ingenta.com/content/nlm?genre=article&issn=0960-1643&volume=51&issue=469&spage=630&aulast=van |issn=}}</ref>
+|-
+| colspan="3" | '''Note:'''<br>† These findings, especially fever, were less sensitive in patients over 60 years of age.<ref name="pmid15728170"/>
+|-
+|}
+Using 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 | pmid= 11088084}}</ref> Unfortunately, even combinations of findings are imperfect. Studies of combining symptoms have included use of recursive partitioning; however, this study combined two cohorts with different prevalences of influenza.<ref name="pmid22427440">{{cite journal| author=Afonso AM, Ebell MH, Gonzales R, Stein J, Genton B, Senn N| title=The use of classification and regression trees to predict the likelihood of seasonal influenza. | journal=Fam Pract | year= 2012 | volume=  | issue=  | pages=  | pmid=22427440 | doi=10.1093/fampra/cms020 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=22427440  }} </ref> 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:
+:
+<table border="1" cellpadding="5" class="wikitable">
+<caption>Combinations of findings for diagnosing influenza<ref name="pmid30843056">{{cite journal| author=Dugas AF, Hsieh YH, Lovecchio F, Moran GJ, Steele MT, Talan DA et al.| title=Derivation and Validation of a Clinical Decision Guideline for Influenza Testing in Four U.S. Emergency Departments. | journal=Clin Infect Dis | year= 2019 | volume=  | issue=  | pages=  | pmid=30843056 | doi=10.1093/cid/ciz171 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=30843056  }} </ref><ref name="pmid22218625">{{cite journal| author=Ebell MH, Afonso AM, Gonzales R, Stein J, Genton B, Senn N| title=Development and validation of a clinical decision rule for the diagnosis of influenza. | journal=J Am Board Fam Med | year= 2012 | volume= 25 | issue= 1 | pages= 55-62 | pmid=22218625 | doi=10.3122/jabfm.2012.01.110161 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=22218625  }} </ref><ref name="pmid15728170"/></caption>
+  <tr>
+    <th rowspan="2">Combinations of findings </th>
+    <th rowspan="2">Sensitivity</th>
+    <th rowspan="2">Specificity</th>
+    <th colspan="2">Projected during local outbreaks<br/>(prevalence approx 66%<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>)
+    </th>
+    <th colspan="2">Projected during influenza season <br/>
+    (prevalence=25%)</th>
+    <th colspan="2">Projected in off-season<br/>
+      (prevalence=2%) </th>
+  </tr>
+  <tr>
+    <th>PPV</th>
+    <th>NPV</th>
+    <th>PPV</th>
+    <th>NPV</th>
+    <th>PPV</th>
+    <th>NPV</th>
+  </tr>
+  <tr>
+    <td>Fever and cough</td>
+    <td align="center">64%<br/>61%<ref name="pmid22218625"/></td>
+    <td align="center">67%<br/>80%<ref name="pmid22218625"/></td>
+    <td align="center">79%<br/>86%<ref name="pmid22218625"/></td>
+    <td align="center">51%<br/>51%<ref name="pmid22218625"/></td>
+    <td align="center">39%<br/>50%<ref name="pmid22218625"/></td>
+    <td align="center">85%<br/>86%<ref name="pmid22218625"/></td>
+    <td align="center">4%<br/>6%<ref name="pmid22218625"/></td>
+    <td align="center">99%<br/>99%<ref name="pmid22218625"/></td>
+  </tr>
+  <tr>
+    <td>Fever and cough and sore throat</td>
+    <td align="center">56</td>
+    <td align="center">71</td>
+    <td align="center">79</td>
+    <td align="center">45</td>
+    <td align="center">39</td>
+    <td align="center">83</td>
+    <td align="center">4</td>
+    <td align="center">98</td>
+  </tr>
+  <tr>
+    <td>Fever and cough and nasal congestion</td>
+    <td align="center">59</td>
+    <td align="center">74</td>
+    <td align="center">81</td>
+    <td align="center">48</td>
+    <td align="center">43</td>
+    <td align="center">84</td>
+    <td align="center">4</td>
+    <td align="center">99</td>
+  </tr>
+<tr>
+    <td>Fever and cough and acute onset<ref name="pmid22218625"/></td>
+    <td align="center">41</td>
+    <td align="center">93</td>
+    <td align="center">92</td>
+    <td align="center">55</td>
+    <td align="center">66</td>
+    <td align="center">83</td>
+    <td align="center">11</td>
+    <td align="center">99</td>
+  </tr>
+<tr>
+    <td>A score of 3 or more from:<br/>• New or increased cough (2 points)<br/>•  Headache (1 point)<br/>• Subjective fever (1 point)<br/>•  Triage temperature >100.4°C (1 point)<ref name="pmid30843056"/></td>
+    <td align="center">92</td>
+    <td align="center">35</td>
+    <td align="center">73</td>
+    <td align="center">69</td>
+    <td align="center">32</td>
+    <td align="center">93</td>
+    <td align="center">3</td>
+    <td align="center">> 99</td>
+  </tr>
+</table>
+====Clinical Prediction Rule====
+Per the bottom row of the table above, a score of 3 or more from<ref name="pmid30843056"/>:
+* New or increased cough (2 points)
+* Headache (1 point)
+* Subjective fever (1 point)
+* Triage temperature >100.4°C (1 point)
 ==References==
 {{Reflist|2}}
+{{WH}}
+{{WS}}
 [[Category:Disease]]
 [[Category:Pulmonology]]
 [[Category:Influenza| ]]
-[[Category:Infectious disease]]
-[[Category:Primary care]]
-{{WH}}
-{{WS}}