Influenza is a rather common viral upper respiratory tract infection among humans. It is caused by influenza A (and less commonly B) viruses, and the pathogenesis, as well as transmission, involves several animal hosts and human-to-human spread through air droplets via inhalation, coughing, or sneezing [1] [2]. After an incubation period of a few days, constitutional symptoms of myalgia, fatigue, malaise, anorexia, fever, and a dry cough are main manifestations of influenza infection and usually last for 7-10 days [1] [3] [4]. It must be noted that the majority of infections are seen during the winter, and rarely in other parts of the year when pandemic or epidemic outbreaks occur [1] [2] [4]. In some patients, the infection is self-limiting, but numerous complications may arise, one of them being influenza pneumonia [1] [2] [3] [4] [5] [6]. It is regarded as the most severe complication and appears more frequently in the presence of various risk factors [5]. In children, concomitant cardiorespiratory illnesses (eg. asthma), diabetes mellitus, immunosuppression, long-term use of aspirin, and other diseases that increase the risk of hypertension are well-established risk factors, whereas pregnancy, chronic diseases, obesity, and residency in chronic care facilities are strongly associated with the development of influenza complications in adults and the elderly [2] [4] [5]. Influenza pneumonia represents the dissemination of the virus into the lower respiratory tract and the lung parenchyma, but secondary bacterial infections of the lungs might also be the culprit in influenza-infected patients, as the virus indirectly promotes bacterial adhesion to the respiratory epithelium [1] [2] [4] [5] [7]. For this reason, a clear distinction between primary influenza pneumonia and secondary bacterial pneumonia may be difficult to make. Nevertheless, approximately 2-5 days after the appearance of signs and symptoms typical for influenza, dyspnea, hypoxia, hemoptysis, cyanosis, and rapidly ensuing acute respiratory distress are hallmarks of influenza pneumonia [2] [3] [4] [8]. In addition, cognitive impairment, gastrointestinal complaints (diarrhea, abdominal pain) and myalgia are reported, and are sometimes the only symptoms, particularly in the elderly population [6]. In fact, pneumonia is one of the most important causes of death from this viral infection, and fatal outcomes might be seen within 24 hours [3] [5] [8] [9].

• Fever

  Getty Images 6/7 Fever Due To Vector Borne Diseases These diseases include malaria, dengue, yellow fever, and chikungunya - all of which have high fever as one of their first symptoms and many others are similar to flu or viral fever. [economictimes.indiatimes.com]

  A 47-year-old man with a fever was highly suspected of having influenza A infection since his wife and son who lived with him had been diagnosed with influenza A. [ncbi.nlm.nih.gov]

  Symptoms include: chills fever hearing loss ear drainage vomiting mood changes An adult with ear pain or discharge should see their doctor as soon as possible. [healthline.com]

• Fatigue

  The patient required mechanical ventilation for 2 days due to respiratory failure and fatigue. Since his recovery from this pneumonia, he has developed obliterative bronchiolitis and currently awaits re-transplantation. [ncbi.nlm.nih.gov]

  Flu symptoms include: Body aches and pains Dry cough Extreme fatigue Fever above 100.4 degrees Headache Pneumonia symptoms include: Bluish fingernails and lips Chills Confusion (most common in older adults) Coughing Decreased appetite Extreme fatigue [piedmont.org]

  Influenza—the flu—is caused by a virus, with symptoms including coughing, fatigue, and fever. While the flu is not typically fatal, it is highly contagious and can be deadly to children, seniors, and other vulnerable populations. [livestories.com]

  Then, they’ll get worse all of a sudden with very high fever, phlegm and fatigue. That can be bacterial pneumonia that can develop after they’ve had the flu. We call that a "super infection." [keranews.org]

  Aches, Pains, and Fatigue Muscle and body aches, headaches, and fatigue are telltale symptoms of the flu, but they can also indicate pneumonia. [dignityhealth.org]

• Sepsis

  More than half of the patients developed sepsis, septic shock, respiratory failure or acute respiratory distress syndrome. The median duration from symptom onset to hospital visit was 3 days, and from hospital visit to death was 4 days. [ncbi.nlm.nih.gov]

  IQV, jolta oli evätty pääsy asiakirjaan, ei voisi vastata tällaisiin kysymyksiin en Infections and infestations Common: sepsis (including fatal outcome), pneumonia (including bacterial, viral, and fungal), upper respiratory tract infection/inflammation [fi.glosbe.com]

  Worldwide, one-third of people who develop sepsis die. [sepsis.org]

  Surviving Sepsis Campaign: international guidelines for management of severe sepsis and septic shock, 2012. Intensive Care Med 2013;39(2):165-228. 26. [bestprac.fi]

• Malaise

  […] might notice a persistent, productive cough (mucus or phlegm comes out), sometimes with yellow-green phlegm; chest pain, particularly during deep breathing; shortness of breath doing things that wouldn't otherwise leave you winded; overall fatigue and malaise [shape.com]

  However, if they are symptomatic, they typically present with sudden onset of high fever, headache, muscle/joint aches, nonproductive cough, and severe malaise. Inflammatory markers are usually normal or slightly elevated. [amboss.com]

  After an incubation period of a few days, constitutional symptoms of myalgia, fatigue, malaise, anorexia, fever, and a dry cough are main manifestations of influenza infection and usually last for 7-10 days. [symptoma.com]

  The clinical features of Mycoplasma pneumonia resemble influenza: The patient has gradual onset of headache, malaise, fever, sore throat, and cough. [mdedge.com]

  The other symptoms, especially cough and malaise, may persist for up to 2 weeks. Unlike adults, children may present with vomiting and diarrhea. [thermofisher.com]

• Hypoxemia

  […] hyponatremia, unexplained metabolic acidosis, elevated lactate, cirrhosis, asplenia Major Criteria • Invasive mechanical ventilation • Septic shock requiring vasopressors Diagnostic Tests • Physical exam: º Crackles or rales, bronchial breath sounds, hypoxemia [empr.com]

  In addition to severity of hypoxemia, further clinical trials would assist in clarifying the survival benefits of prone positioning in the specific risk factors. [annalsofintensivecare.springeropen.com]

  Bacteria: most frequently Streptococcus pneumoniae, but also other typical pneumonia pathogens such as S. aureus and Haemophilus influenzae Signs suggestive of secondary infection with S. aureus Hyperacute onset of symptoms Hypoxemia Hemoptysis Multiple [amboss.com]

  Hypoxemia increases progressively to the point of respiratory failure requiring intubation and mechanical ventilation, often after only one day of hospitalization [14]. [ncbi.nlm.nih.gov]

• Cough

  Conclusions: For outpatient adults with acute cough due to suspected pneumonia, we suggest the following clinical symptoms and signs are suggestive of pneumonia: cough; dyspnea; pleural pain; sweating, fevers, or shivers; aches and pains; temperature [mayoclinic.pure.elsevier.com]

  The Expert Cough Panel agreed on the following clinical symptoms as criteria suggestive of pneumonia in outpatient adults: cough, dyspnea, pleural pain, sweating, shivers, aches, temperature of ≥38°C, tachypnea, and new and localizing chest examination [clinicaladvisor.com]

  But a cough that lasts more than two weeks — or is accompanied by a high fever, shortness of breath, chest pain or coughing up blood — needs prompt attention, particularly during the winter months, when influenza is rampant. [aarp.org]

  You may also experience pain in your ribs from frequent, hard coughing. Coughing – Both the flu and pneumonia cause coughing. A flu cough is likely to be a dry cough. A pneumonia cough is likely to bring up phlegm that has built up in your lungs. [augustahealth.com]

  Cough on the other hand, is also a major symptom of pneumonia. However, the cough in case of pneumonia is different from flu. Pneumonia cough will also cause dark coloured phlegm which may even contain blood. [ndtv.com]

• Dyspnea

  Case Report: We report a case of a 78-year-old woman admitted to the emergency department in January 2007 for fever and dyspnea. On admission, she had a temperature of 38.8°C and dyspnea. There were wheezing on auscultation. [amjcaserep.com]

  Pure influenza viral pneumonia was observed in 94 cases, which were most frequently young adults with chief complaints of non-productive cough and dyspnea. Radiological imaging showed diffuse ground-glass opacity. [ncbi.nlm.nih.gov]

  Conclusions: For outpatient adults with acute cough due to suspected pneumonia, we suggest the following clinical symptoms and signs are suggestive of pneumonia: cough; dyspnea; pleural pain; sweating, fevers, or shivers; aches and pains; temperature [mayoclinic.pure.elsevier.com]

  The Expert Cough Panel agreed on the following clinical symptoms as criteria suggestive of pneumonia in outpatient adults: cough, dyspnea, pleural pain, sweating, shivers, aches, temperature of ≥38°C, tachypnea, and new and localizing chest examination [clinicaladvisor.com]

  Nevertheless, approximately 2-5 days after the appearance of signs and symptoms typical for influenza, dyspnea, hypoxia, hemoptysis, cyanosis, and rapidly ensuing acute respiratory distress are hallmarks of influenza pneumonia. [symptoma.com]

• Dry Cough

  Although her clinical and laboratory findings were consistent with the diagnosis of H1N1 pneumonia, e.g., fever, sore throat, dry cough, arthralgias, myalgias, thrombocytopenia, relative lymphopenia, and elevated serum transaminases, some findings suggested [ncbi.nlm.nih.gov]

  […] a more severe dry cough that produces small amounts of mucus > A bluish color to the lips; this occurs in some cases These are symptoms of the flu: > Headache > Chills > Dry cough > Muscle aches (myalgia) > Fever > Stuffy nose > Sore throat The fever [weather.com]

  You may also experience pain in your ribs from frequent, hard coughing. Coughing – Both the flu and pneumonia cause coughing. A flu cough is likely to be a dry cough. A pneumonia cough is likely to bring up phlegm that has built up in your lungs. [augustahealth.com]

  After an incubation period of a few days, constitutional symptoms of myalgia, fatigue, malaise, anorexia, fever, and a dry cough are main manifestations of influenza infection and usually last for 7-10 days. [symptoma.com]

  Learn more Cryptogenic Organizing Pneumonia (COP) Symptoms, Causes and Risk Factors The cause of COP is unknown and in most cases, gradual onset of shortness of breath and dry cough are the most common symptoms. [lung.org]

• Tachypnea

  Conclusions: For outpatient adults with acute cough due to suspected pneumonia, we suggest the following clinical symptoms and signs are suggestive of pneumonia: cough; dyspnea; pleural pain; sweating, fevers, or shivers; aches and pains; temperature ≥ 38°C; tachypnea [mayoclinic.pure.elsevier.com]

  The Expert Cough Panel agreed on the following clinical symptoms as criteria suggestive of pneumonia in outpatient adults: cough, dyspnea, pleural pain, sweating, shivers, aches, temperature of ≥38°C, tachypnea, and new and localizing chest examination [clinicaladvisor.com]

  These factors are being male, thoracic pain, hypothermia, systolic hypotension, tachypnea, diabetes, neurologic disease, cancer, leukopenia, and multilobar infiltration [4, 13, 15, 29]. [hindawi.com]

  Her condition then rapidly deteriorated with development of fever to 38.5°C, hemodynamic instability (sinus tachycardia to 160 beats per minute, blood pressure of 82/53), and respiratory decompensation (tachypnea of 62 breaths per minute, oxygen saturation [frontiersin.org]

  When pneumonia develops, cough, followed by dyspnea, tachypnea, and chest pain, are reported. [medscape.com]

• Rales

  Rales and decreased breath sounds in lung segments are best heard with deep breaths. [mdedge.com]

  Physical examination may demonstrate evidence of conjunctivitis, nasal discharge, hyperemic pharyngeal mucosa without exudate, cervical adenopathy, and, rarely, rales. [thermofisher.com]

  If patients have lower respiratory tract symptoms and signs (eg, dyspnea, rales noted during lung examination), pulse oximetry to detect hypoxemia and a chest x-ray to detect pneumonia should be done. [merckmanuals.com]

  […] alcoholism/alcoholic withdrawal, hyponatremia, unexplained metabolic acidosis, elevated lactate, cirrhosis, asplenia Major Criteria • Invasive mechanical ventilation • Septic shock requiring vasopressors Diagnostic Tests • Physical exam: º Crackles or rales [empr.com]

  Harsh breath sounds from the larger airways that are transmitted through the inflamed lung are termed bronchial breathing and are heard on auscultation with a stethoscope.[20] Crackles (rales) may be heard over the affected area during inspiration.[20 [en.wikipedia.org]

• Chest Pain

  Young healthy adults without a cardiac history who have H1N1 and chest pain usually have either acute myocardial infarction or acute myocarditis. [ncbi.nlm.nih.gov]

  “Both can have the symptoms of coughing, fever and chest pain.” [health.clevelandclinic.org]

  If the doctor diagnoses bacterial pneumonia, treatment typically includes antibiotics and possibly other medications to help relieve coughing and chest pain. [weather.com]

  Soreness and Pain – Muscle soreness is common with flu symptoms. Pneumonia typically causes pain in the chest. You may also experience pain in your ribs from frequent, hard coughing. Coughing – Both the flu and pneumonia cause coughing. [augustahealth.com]

  The most common, similar signs and symptoms of lung cancer and pneumonia are cough, chest pain or discomfort, and shortness of breath. [emedicinehealth.com]

• Tachycardia

  With H1N1 pneumonia, clinicians should be alert for otherwise unexplained tachycardia or chest pain that may represent acute myocardial infarction or myocarditis. [ncbi.nlm.nih.gov]

  She was ill-appearing in mild respiratory distress with left lower lung field crackles, tachycardia without murmurs, and bilateral lower extremity pitting edema. [frontiersin.org]

  The latter presented more frequently with fever and tachycardia. [erj.ersjournals.com]

• Cyanosis

  After typical symptoms of upper respiratory tract infection and fever appear, severe respiratory decline with hypoxia and cyanosis can ensue without early recognition and appropriate therapy. [symptoma.com]

  […] that usually worsens when taking a deep breath, known as pleuritic pain fast heartbeat fatigue and weakness nausea and vomiting diarrhea sweating headache muscle pain confusion or delirium, especially in older adults dusky or purplish skin color, or cyanosis [medicalnewstoday.com]

  The symptoms may worsen with time, and new respiratory symptoms, such as dyspnea and cyanosis, may appear. This form is the least common but the most severe in terms of pulmonary complications. [medscape.com]

• Confusion

  CAP severity scores PSI (Pneumonia Severity Index), CURB-65 (confusion, urea, respiratory rate, blood pressure, age ≥ 65 years) and CRB-65 (confusion, respiratory rate, blood pressure, age ≥ 65 years) were calculated. [ncbi.nlm.nih.gov]

  “It’s easy for patients to confuse the flu and pneumonia,” says Dr. Atoyebi. “We see that all the time. When people have upper respiratory symptoms like a cough, runny nose or wheezing, they often come in concerned about pneumonia or flu.” [piedmont.org]

  What could be fueling the confusion is that norovirus is often referred to as the stomach flu – but, in fact, there is no such thing as stomach flu. [belmarrahealth.com]

  Headache and Confusion Headaches, sometimes severe, can occur with both flu and pneumonia. Confusion, difficulty with short-term memory, or other changes in cognition sometimes occur with pneumonia, especially for seniors 65 and older. Viral vs. [arcare.net]

• Tremor

  Symptoms include: severe headache high fever vomiting light sensitivity drowsiness clumsiness Though rare, this condition may also cause tremors and difficulty with movement. [healthline.com]

Mortality rates of influenza pneumonia are very high without early therapy, thus a detailed and comprehensive clinical, radiological, and microbiological assessment is vital in preventing the onset of respiratory decline. Firstly, physicians must obtain a complete patient history that will note the course and progression of symptoms and reveal any preexisting comorbidities that could predispose patients to a more severe form of infection. The physical examination is important in guiding the physician toward the lungs as the primary source of infection, after which both imaging studies and microbiological evaluation are necessary. Plain radiography is a valuable tool for visualizing the changes in the lung parenchyma for many infections, including influenza, and bilateral reticular or reticulonodular opacities, as well as patchy areas of consolidation (although other authors suggest that consolidation is absent) are principal features of influenza pneumonia [2] [3] [5] [9]. Unfortunately, not all patients exhibit typical X-ray findings [6]. Thus, confirmation of influenza virus as the underlying cause through microbiological testing is crucial. Several tests are available [1] [2] [5] [6]:

• Rapid influenza diagnostic test (RIDT) - Very fast results (within 15-30 minutes), the ability to discern between influenza A and B, and very high specificity are the reasons why RIDT is quite often performed in standard practice [1] [3] [4] [5].
• Reverse transcriptase-polymerase chain reaction (RT-PCR) - Although it is more expensive and requires advanced technical equipment, the RT-PCR test detects viral genetic material and possesses very high sensitivity and specificity rates [2] [5]. Because of its fast turnaround time (1-4 hours), it is considered to be the optimal diagnostic procedure [3] [5].
• Viral culture - Long waiting times (several days) are the main limitation of viral cultivation in the setting of influenza pneumonia, despite the fact that the specificity rate is virtually 100%. However, newly designed tests can yield conclusive results within 1-3 days [5].
• Serology - Detection of specific influenza antibodies is now being replaced by faster and more reliable methods for the diagnosis of influenza, and serology is often used as a retrospective analysis [5].

• Pulmonary Infiltrate

  Early diagnosis of the pulmonary infiltrates was accomplished by obtaining bronchial secretions with fiberoptic bronchoscopy and staining them with influenza-A fluorescent conjugate. [ncbi.nlm.nih.gov]

  […] eosinophilia due to drugs (J70.2-J70.4) pulmonary eosinophilia due to specified parasitic infection (B50-B83) pulmonary eosinophilia due to systemic connective tissue disorders (M30-M36) pulmonary infiltrate NOS (R91.8) J82) aspiration pneumonia NOS [icd10data.com]

  We have adapted a scoring system described by Opravil to grade the severity of pulmonary infiltrates in CXR: each lung is divided into four equal quadrants and each quadrant is scored on a scale of 0–3 (0: normal, 1: subtle increase interstitial markings [journalpulmonology.org]

• Bilateral Pulmonary Infiltrates

  The initial chest radiograph may be normal, but several days later, bilateral pulmonary infiltration indicating pulmonary edema develops (55). Pleural effusion is common. [pubs.rsna.org]

• Leukopenia

  […] findings were consistent with the diagnosis of H1N1 pneumonia, e.g., fever, sore throat, dry cough, arthralgias, myalgias, thrombocytopenia, relative lymphopenia, and elevated serum transaminases, some findings suggested an alternate diagnosis, e.g., leukopenia [ncbi.nlm.nih.gov]

  […] necessitating vasopressors, or acute respiratory failure requiring intubation and mechanical ventilation º ICU admission recommended: 1 major criteria or 3 minor criteria are present Severe CAP Criteria Minor Criteria • Hypothermia ( • PaO 2 /FiO 2 ratio ≤250 • Leukopenia [empr.com]

  Three of the four had significant leukopenia (WBC < 1.0 × 103/L). Type A influenza virus pneumonia was confirmed in all patients by findings of a direct fluorescent antibody against influenza virus in bronchoalveolar lavage fluid. [ajronline.org]

  Significant differences also related to the inflammatory response, with more novel H1N1 patients having leukocyte counts <10,000 cells·μL−1 (61.6% versus 32.7%; p = 0.001) or leukopenia (<4,000 cells·μL−1) (13.7% versus 0%; p = 0.005). [erj.ersjournals.com]

The range of absolute risk differences in mortality between the early treatment group and the late treatment group was 26% to 50% (pooled risk difference, 41% [CI, 29% to 54%]). [ncbi.nlm.nih.gov]

In outpatient adults with acute cough and suspected influenza, the panel suggests antiviral treatments within 48 hours; antiviral treatments may be linked to lower use of antibiotics, fewer hospitalizations, and optimal outcomes. [clinicaladvisor.com]

In patients with seasonal influenza, treatment was as follows. [erj.ersjournals.com]

The prevention and treatment of influenza as control strategies aid in reducing the transmission and in treatment of those who are already infected; however, the treatment poses a danger of development of drug resistance. [hindawi.com]

Moreover, metabolomics is a highly sensitive and specific tool for the 90-day prognosis of mortality in H1N1 pneumonia. [ncbi.nlm.nih.gov]

Plasma metabolomics for the diagnosis and prognosis of H1N1 influenza pneumonia. Crit. Care. 21:97 (2017) [bioanalysis-zone.com]

Prognosis Prevention Influenza vaccine Recommendation Annual flu shot for all persons aged 6 months and older every flu season as soon as the vaccine becomes available Egg allergy is no longer considered a contraindication Vaccines Live attenuated or [amboss.com]

[…] been described 2 : initial chest radiographs usually show central or peripheral pulmonary ground-glass opacities (GGO) and consolidations that have a patchy or nodular appearance multizonal and bilateral peripheral opacities are associated with adverse prognosis [radiopaedia.org]

Differentiation between a bacterial and viral etiology for the pulmonary infiltrates frequently presents a diagnostic dilemma. Rapid diagnosis is essential; and once established, the patient requires careful supportive therapy. [ncbi.nlm.nih.gov]

When pneumonia is documented, another reason for a query would be to identify the etiology of the pneumonia. Documented etiology could change the MS-DRG assignment. [hcpro.com]

Indications of the Etiology or Etiologies of Pneumonia in Patients with Influenza-Related Lower Respiratory Tract Disease. [nejm.org]

All have agreed as to the uniform character of the disease influenza wherever it has appeared in its swing across the continent, but conflicting views have been presented as to its etiology and as to the relation of various bacteria discovered in the [jamanetwork.com]

Research Article Epidemiology Sourya Shrestha 1, 2, *, Betsy Foxman 3, Daniel M. [stm.sciencemag.org]

Rohani is a professor of ecology and evolutionary biology, a professor of complex systems and a professor of epidemiology at the School of Public Health. [ns.umich.edu]

The recent epidemiology findings have helped to partially resolve the contribution of different pathogens. [journals.lww.com]

Article Figures/Media 22 Citing Articles Article We are now facing a pandemic caused by an epidemiologically distinct, novel virus, the 2009 pandemic influenza A (H1N1) virus (swine flu), against which few persons born since 1970 have antibodies. [nejm.org]

INTRODUCTION: Comparisons of the characteristics between the influenza A (H1N1) pdm09 and common seasonal influenza are important for both clinical management and epidemiological studies. [ncbi.nlm.nih.gov]

Etiology Virus: Influenza virus A and B (and rarely influenza C) Person-to-person transmission: directly via respiratory droplets (sneezing or coughing) or indirectly through contact with contaminated surfaces References:[2][3] Classification Pathophysiology [amboss.com]

Out of this work, the distinction between viral and bacterial strains was noticed.[8] Pathophysiology[edit] Viruses must invade cells in order to reproduce. [en.wikipedia.org]

《Pathophysiology: The Biologic Basis for Disease in Adults and Children》 7판. Elsevier Health Sciences. 498쪽. [ko.wikipedia.org]

The pathophysiology of such conditions is most likely attributable to her overall degree of critical illness as well as bacterial coinfection with MRSA, but is also within the realm of influenza-associated morbidity (6, 15–19), especially in non-vaccinated [frontiersin.org]

Centers for Disease Control and Prevention (CDC). Available at http://www.bt.cdc.gov/HAN/han00347.asp. Accessed: July 22, 2013. Preventing Seasonal Flu With Vaccination. Centers for Disease Control and Prevention. [medscape.com]

Prevention To prevent contracting the flu people can take everyday precautions such as regularly washing their hands and avoiding those who are sick, but the best way to prevent the flu is by receiving the flu vaccination every year. [statista.com]

The Centers for Disease Control and Prevention (CDC) recommends annual influenza vaccinations for everyone age 6 months or older. [news.vanderbilt.edu]

Control by Prevention Measures Only Simulations are done when there is no control strategy in place and when there are controls involving prevention of wild-type influenza strain, prevention of influenza resistant strain, and prevention of pneumonia. [hindawi.com]

“Infection risk can be modified through the use of preventive measures or appropriate management protocols. [contagionlive.com]

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