Influenza history and symptoms
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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
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.
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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]
| 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 | Sensitivity | Specificity | Projected during local outbreaks (prevalence approx 66%[13][14]) |
Projected during influenza season (prevalence=25%) |
Projected in off-season (prevalence=2%) |
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|---|---|---|---|---|---|---|---|---|
| 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.