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Influenza

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Influenza is acommon infectious disease caused by the Influenza virus.


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Onset is sudden with fever, rhinorrhea, sore throat and headache. Severe myalgias coupled with respiratory tract symptoms are typical of influenza [7]. Patients may also have red, watery eyes and cough. There can also be tachycardia and dyspnea but with hypotension. Vomiting and diarrhea may also occur, but are rare findings associated with the disorder.

Cough
  • It causes a fever, runny nose, sore throat, cough, headache, muscle aches (myalgias), and a general feeling of illness (malaise).[merckmanuals.com]
  • Yet differing symptoms of the cold are: sore throat; productive, phlegmy coughs; and sneezing.[3dscience.com]
  • […] mild to moderate, hacking cough common; often severe with painful cough For most people, the flu lasts 1 or 2 weeks, but it can last for up to 1 month.[medbroadcast.com]
  • If you don't have a tissue, cough or sneeze into your elbow or sleeve. Wash your hands often with soap and water, especially after you cough or sneeze. If you don't have soap and water, you can use an alcohol-based hand cleaner.[girlshealth.gov]
  • Perform good cough etiquette at all times. This includes coughing into a tissue and disposing of it immediately, or coughing into your sleeve. Good hand hygiene is also important.[betterhealth.vic.gov.au]
Sneezing
  • If you don't have a tissue, cough or sneeze into your elbow or sleeve. Wash your hands often with soap and water, especially after you cough or sneeze. If you don't have soap and water, you can use an alcohol-based hand cleaner.[girlshealth.gov]
  • Contain your coughs and sneezes. Cover your mouth and nose when you sneeze or cough. To avoid contaminating your hands, cough or sneeze into a tissue or into the inner crook of your elbow. Avoid crowds.[mayoclinic.org]
  • Sneeze into your elbow Sneeze into your elbow instead of your hands, or cover your face with a tissue when you cough or sneeze and throw used tissues in a rubbish bin. Clean your hands Wash your hands thoroughly and often.[health.nsw.gov.au]
  • The virus is spread by inhaling droplets coughed or sneezed out by an infected person or by having direct contact with an infected person's nasal secretions.[merckmanuals.com]
Common Cold
  • Due to the fact that influenza infections and common colds spread easily via droplets and contact, public prevention measures, such as hand washing and facial masks, are recommended for influenza prophylaxis.[ncbi.nlm.nih.gov]
  • How can I tell the difference between a common cold and influenza? Many cold and influenza symptoms are similar. Both common cold and influenza are caused by viruses. There are some differences with influenza.[my.clevelandclinic.org]
  • Influenza is distinctly different from the common cold (see Common Cold ). It is caused by a different virus and produces symptoms that are more severe. Also, influenza affects cells much deeper down in the respiratory tract.[merckmanuals.com]
  • Unlike the common cold, the flu can cause serious illness and can be life-threatening. Each year, influenza is estimated to be responsible for at least 9 million cases of disease, 140,000 hospitalizations, and 12,000 deaths.[healthvermont.gov]
  • Symptoms of the flu come on suddenly and are worse than those of the common cold. They may include Body or muscle aches Chills Cough Fever Headache Sore throat Is it a cold or the flu? Colds rarely cause a fever or headaches.[medlineplus.gov]
Dry Cough
  • The dry cough and fatigue of influenza can last two to three weeks. Signs that influenza is getting worse include fever, shaking chills, and shortness of breath.[my.clevelandclinic.org]
  • Influenza symptoms often begin suddenly, with fever, headache, tiredness, dry cough, sore throat, nasal congestion and body aches. The best way to prevent influenza is to get vaccinated each year.[dhs.wisconsin.gov]
  • Infected individuals usually experience a rapid onset of flu symptoms which typically include: muscle aches, high fever, head ache, chills, fatigue, dry cough and runny/stuffy nose.[3dscience.com]
  • A bout of the flu typically follows this pattern: Days 1–3: Sudden appearance of fever, headache, muscle pain and weakness, dry cough, sore throat and sometimes a stuffy nose. Day 4: Fever and muscle aches decrease.[betterhealth.vic.gov.au]
  • The symptoms of flu can include: fever sore throat dry cough headache muscle and joint pain tiredness or extreme exhaustion In the elderly, fever may be absent and the only signs and symptoms of flu may be: confusion shortness of breath worsening of a[conditions.health.qld.gov.au]
Nasal Congestion
  • Influenza usually comes on suddenly and may include these symptoms: fever, headache, malaise (a feeling of being ill and without energy that can be extreme), cough, sore throat, nasal congestion and body aches.[fda.gov]
  • Influenza symptoms often begin suddenly, with fever, headache, tiredness, dry cough, sore throat, nasal congestion and body aches. The best way to prevent influenza is to get vaccinated each year.[dhs.wisconsin.gov]
  • Common signs and symptoms of the flu include: Fever over 100.4 F (38 C) Aching muscles, especially in your back, arms and legs Chills and sweats Headache Dry, persistent cough Fatigue and weakness Nasal congestion Sore throat When to see a doctor Most[mayoclinic.org]
  • The most common side effects seen with administration of the nasal vaccine include runny nose or nasal congestion in recipients of all ages, fever more than 100 degrees Fahrenheit in children two to six years of age, and sore throat in adults.[fda.gov]
Fever
  • ‘It also caused post-flood diseases for children like influenza, diarrhea and fever.’ ‘Other viral illnesses include influenza, the common cold, Lassa fever, and ebola.’[en.oxforddictionaries.com]
  • You can also take medicine to relieve aches and fever. Do not give aspirin to children with fever. The drug of choice for children is acetaminophen. Rest. Bed rest and increased intake of fluids.[cedars-sinai.org]
  • Stay home at least 24 hours after your fever goes away to make sure that it's not coming back. (It counts only if your fever stays down by itself, without help from medicines that lower fever.) Read more about treating the flu .[girlshealth.gov]
  • Moderate to high fever Dry cough Headache Sore throat Chills Runny nose Loss of appetite Muscle aches Tiredness Many conditions — such as a common cold, diarrhea, and vomiting — are called "the flu," but are not influenza.[my.clevelandclinic.org]
  • […] for at least 24 hours without the use of a fever-reducing medicine.[kidshealth.org]
Chills
  • Moderate to high fever Dry cough Headache Sore throat Chills Runny nose Loss of appetite Muscle aches Tiredness Many conditions — such as a common cold, diarrhea, and vomiting — are called "the flu," but are not influenza.[my.clevelandclinic.org]
  • They may include Body or muscle aches Chills Cough Fever Headache Sore throat Is it a cold or the flu? Colds rarely cause a fever or headaches. Flu almost never causes an upset stomach.[fpnotebook.com]
Fatigue
  • An 88-year-old woman presented to our emergency room with complaints of fever, coryza, barking cough and generalised fatigue for 2 days. Physical examination showed stridor, tachypnoea with use of accessory muscles of respiration on admission.[ncbi.nlm.nih.gov]
  • Infected individuals usually experience a rapid onset of flu symptoms which typically include: muscle aches, high fever, head ache, chills, fatigue, dry cough and runny/stuffy nose.[3dscience.com]
  • 1 a : an acute, highly contagious, respiratory disease caused by any of three orthomyxoviruses: ( 1 ) or influenza A : moderate to severe influenza that in humans is marked especially by sudden onset, fever, sore throat, fatigue, muscle aches, inflammation[merriam-webster.com]
  • People infected with the seasonal flu virus feel miserable with fever, chills, muscle aches, coughing, congestion, headache and fatigue for a week or so.[niaid.nih.gov]
High Fever
  • Moderate to high fever Dry cough Headache Sore throat Chills Runny nose Loss of appetite Muscle aches Tiredness Many conditions — such as a common cold, diarrhea, and vomiting — are called "the flu," but are not influenza.[my.clevelandclinic.org]
  • Infected individuals usually experience a rapid onset of flu symptoms which typically include: muscle aches, high fever, head ache, chills, fatigue, dry cough and runny/stuffy nose.[3dscience.com]
  • People usually become very sick with several, or all, of the following symptoms: Cough, often becoming severe Extreme exhaustion Fatigue for several weeks Headache High fever Runny or stuffy nose Severe aches and pains Sneezing at times Sometimes a sore[cedars-sinai.org]
  • fever for more than three days If you are at high risk for developing complications, your doctor may want you to take antiviral medications, such as Tamiflu.[sepsis.org]
  • See your doctor or call 13 HEALTH (13 43 25 84) if you: are concerned about your symptoms are in a high-risk group and have a cough and or high fever (38 degrees Celsius or more) that is not improving Health outcome Most people recover from the flu within[conditions.health.qld.gov.au]
Weakness
  • A bout of the flu typically follows this pattern: Days 1–3: Sudden appearance of fever, headache, muscle pain and weakness, dry cough, sore throat and sometimes a stuffy nose. Day 4: Fever and muscle aches decrease.[betterhealth.vic.gov.au]
  • Fever, cough, shaking chills, body aches, and extreme weakness are common symptoms. • You can catch influenza from people who cough, sneeze, or even just talk around you.[vaccineinformation.org]
  • Cough, weakness, sweating, and fatigue may persist for several days or occasionally weeks.[merckmanuals.com]
  • Influenza A symptoms If you have influenza, you will have some or all of these symptoms: fever and chills headache and muscle aches feeling tired and weak sneezing, and stuffy or runny nose sore throat and cough Children may also have abdominal pain,[healthdirect.gov.au]
  • After 5 days, fever and other symptoms have usually disappeared, but a cough and weakness may continue. All symptoms usually are gone within a week or two.[kidshealth.org]
Loss of Appetite
  • Moderate to high fever Dry cough Headache Sore throat Chills Runny nose Loss of appetite Muscle aches Tiredness Many conditions — such as a common cold, diarrhea, and vomiting — are called "the flu," but are not influenza.[my.clevelandclinic.org]
  • Other common symptoms include sore throat, runny nose, headache, chills, loss of appetite, and fatigue. Some adults will also experience stomach ache, vomiting and diarrhea, but these symptoms are more common with children.[ccohs.ca]
  • Other symptoms can be: chills aching behind the eyes loss of appetite sore throat runny or stuffy nose.[betterhealth.vic.gov.au]
  • Symptoms, which usually begin about 2 days after exposure to the virus, can include: fever chills headache muscle aches dizziness loss of appetite tiredness cough sore throat runny nose nausea or vomiting weakness ear pain diarrhea Infants with the flu[kidshealth.org]
Abdominal Pain
  • Influenza A symptoms If you have influenza, you will have some or all of these symptoms: fever and chills headache and muscle aches feeling tired and weak sneezing, and stuffy or runny nose sore throat and cough Children may also have abdominal pain,[healthdirect.gov.au]
  • pain in children Rare Mild Children are more likely to have gastrointestinal symptoms (nausea, vomiting and diarrhoea).[conditions.health.qld.gov.au]
Chest Pain
  • You should also get help straight away if you feel chest pain , short of breath, dizzy or confused , or you are vomiting a lot.[healthdirect.gov.au]
  • When to call the doctor You should consult your doctor if symptoms such as clouded/altered consciousness, breathlessness, or severe chest pain occur, and if you are concerned.[medinfo.co.uk]
  • See your doctor if you are concerned, and seek immediate medical attention if you experience any of the following symptoms: difficulty breathing chest pain sudden dizziness confusion severe vomiting fever with a rash.[betterhealth.vic.gov.au]
  • Danger signs Seek urgent medical advice if you have: a high fever that doesn’t come down, especially if you are pregnant chills or severe shaking difficulty breathing or chest pain purple or bluish discolouration of your lips, skin, fingers or toes seizures[health.govt.nz]
Tachycardia
  • There can also be tachycardia and dyspnea but with hypotension. Vomiting and diarrhea may also occur, but are rare findings associated with the disorder.[symptoma.com]
  • Typical signs and symptoms include the following (not necessarily in order of prevalence): Cough and other respiratory symptoms Fever Sore throat Myalgias Headache Nasal discharge Weakness and severe fatigue Tachycardia Red, watery eyes Cough and other[emedicine.medscape.com]
Photophobia
  • Ocular symptoms develop in some patients with influenza and include photophobia, burning sensations, or pain upon motion. Some patients with influenza develop rhinitis of varying severity, but it is generally not the chief symptom.[emedicine.medscape.com]
Flushing
  • The skin may be warm and flushed, especially on the face. The mouth and throat may redden, the eyes may water, and the whites of the eyes may become bloodshot. People, especially children, may have nausea and vomiting.[merckmanuals.com]
Myalgia
  • It is marked by inflammation of the NASAL MUCOSA; the PHARYNX; and conjunctiva, and by headache and severe, often generalized, myalgia.[fpnotebook.com]
  • It causes a fever, runny nose, sore throat, cough, headache, muscle aches (myalgias), and a general feeling of illness (malaise).[merckmanuals.com]
  • Women are followed throughout pregnancy through twice weekly surveillance for influenza symptoms (  1 of myalgia, cough, runny nose, sore throat, or difficulty breathing) and have mid-turbinate nasal swabs collected for influenza virus testing during[ncbi.nlm.nih.gov]
  • Influenza is an acute viral disease of the respiratory tract which is characterized by fever, headache, myalgia, prostration, coryza, sore throat and cough.[ncbi.nlm.nih.gov]
Headache
  • They may include Body or muscle aches Chills Cough Fever Headache Sore throat Is it a cold or the flu? Colds rarely cause a fever or headaches. Flu almost never causes an upset stomach.[fpnotebook.com]
Guillain-Barré Syndrome
  • After the 1976 swine flu epidemic, in which millions of people received the influenza vaccine, a larger than usual number of people had a nerve disorder called Guillain-Barré syndrome (see Guillain-Barré Syndrome (GBS) ).[merckmanuals.com]
  • […] eggs People who have had a severe reaction in the past after getting the flu shot People who are sick with a fever (these people should get vaccinated after they have recovered) Babies who are age 6 months old or younger People who have a history of Guillain-Barré[cedars-sinai.org]
  • Talk to your doctor to see if the vaccine is still recommended if your child: has ever had a severe reaction to a flu vaccination has Guillain-Barré syndrome (a rare condition that affects the immune system and nerves) In the past, it was recommended[kidshealth.org]
  • Individuals who developed Guillain-Barré Syndrome within 6 weeks of receiving a flu vaccine. Children under 6 months old. Individuals experiencing a fever with a moderate-to-severe illness should wait until they recover before being vaccinated.[medicalnewstoday.com]

Workup

Laboratory tests

  • Complete blood count
  • Nasal or throat wash
  • Nasal or throat swab
  • PCR
  • Cell-culture based tests
  • FLU OIA test and QUICKVUE Influenza test based on detection of viral antigens by using monoclonal antibodies [7].
  • ZSTATFLU test based on detection of viral neuraminidase using a substrate of colour-changing enzyme.
  • Alere I Influenza A & B test a new point-of-care influenza test that delivers highly accurate molecular results in less than 15 minutes, approved by FDA in June 2014.

Imaging 

Imaging studies are generally not required. In case of complications such as bacterial pneumonia, chest radiography may be advised.

Test results

A clinical examination and history is sufficient to form a diagnosis. Laboratory tests can help confirm the diagnosis.

Treatment

Pharmacological treatment

Lam et al suggested that cases of suspected severe influenza infection should be treated early and aggressively, even before diagnostic tests can be confirmed [8]. Commonly used antivirals include neuraminidase inhibitors like oseltamivir and zanamivir. M2 protein ion channel inhibitors, which are adamantine derivatives, like amantidine and rimantidine can also be used. Due to a marked increase in resistant isolates, the Advisory Committee on Immunization Practices (ACIP) recommends that adamantanes not be used in the United States for the treatment of influenza, except in selected circumstances [9].

Non-pharmacological treatment

It includes bed rest, the increased intake of fluids and a light but healthy diet during the flu. Typically, flu will resolve within a few days without any treatment.

Prognosis

Influenza has an excellent prognosis. Like all infectious diseases, it has a certain duration of action after which the symptoms begin to slowly subside. When there are no complications, acute symptoms subside within 3-7 days. Post-influenza asthenia may last for a few weeks.

The mortality associated with influenza is due to the complications associated with the disease. As a result of these complications, influenza can be deadly, especially for the weak, young and old, or chronically ill [6]. They include bacterial pneumonia, bronchitis, myositis, Reye syndrome in children, myocarditis and in some rare cases, multiorgan failure.

Etiology

Causative factors

There are 3 basic causative factors of this disease: Influenza A, B and C virus. They belong to the Orthomyxovirus family. Of the three, Influenza A virus is considered to be the most pathogenic and has at least 4 different recognized strains.

Transmission

Although the respiratory tract is presumed to be the primary site for the acquisition of infection, one study has suggested that transocular entry of influenza virus can occur [2]. Infection can be transmitted through sneezing and coughing and is thought to be transmitted primarily via large particle droplets (>5 microns) [3]. It is an airborne infection and close contact with a person with an active infection can transmit the disease.

Epidemiology

Incidence

According to a recent estimate by World Health Organization, 3 to 5 million cases of severe cases occur worldwide annually. 250,000 to 500,000 deaths have also been reported [4].

Age

Influenza affects young and old alike. Elderly patients with low immunity and immunocompromised individuals are particularly susceptible.

Sex

Influenza occurs equally in both sexes.

Sex distribution
Age distribution

Pathophysiology

Influenza A is a genetically labile virus with mutation rates as high as 300 times that of other microbes [5]. It is known to cause pandemics worldwide. Influenza B is usually associated with smaller outbreaks. Influenza C has been reported to cause epidemics in children but mainly causes only mild respiratory infections.

After the virus has been inhaled, an incubation period of 12-24 hours ensues. A special substance present in the form of spikes on the virus is hemagglutinin. It binds to cell surface receptors to initiate infection. Another substance, neuroaminidase, present in the virus is an enzyme that degrades the protective layer of mucus in the respiratory tract. It also cleaves neuraminic acid to release progeny virus from the infected cells. It is the action of these two moieties that result in the symptoms of influenza as well as necrosis of the superficial layers of the respiratory epithelium.

Prevention

The main mode of prevention is the influenza vaccine that typically contains two strains of Influenza A virus and one strain of Influenza B virus. Annual influenza vaccination is an important public health measure for preventing influenza infection [10]. Currently, there are two types of vaccines available in the US. First is a killed vaccine containing purified protein subunits of the virus (hemagglutinin and neuraminidase). It has two versions, namely ‘split virus’ vaccine and ‘purified subunit’ vaccine. Both are administered intramuscularly. The second type is a live vaccine which contains temperature sensitive mutants of Influenza A and B virus. 

Some antiviral drugs may also help in preventing the infection, particularly in elderly, non-vaccinated individuals.

Summary

Influenza is a common household occurrence. Commonly known as the ‘flu’, influenza is an infectious disease caused by a virus. Although it is often confused with other influenza-like illnesses, especially the common cold, influenza is a more severe disease [1]. It has been known to cause epidemics and pandemics worldwide. Influenza has a seasonal variation, being much more common in winter and in the rainy season. It has variations which pose to be a much bigger threat like the avian flu and the swine flu, however, our section deals with the general concept of this disease.

Patient Information

Definition

Influenza, simply called the flu, is a very common infectious disease of viral origin.

Cause

It is caused by Influenza virus A, B or C. Transmission is through airborne aerosol droplets that contain the infectious particles. It can be spread by close contact with a person having an active infection. Simple acts such as coughing, sneezing and even laughing can transmit the infection.

Signs and symptoms

Signs and symptoms include sudden high grade fever associated with chills, sore throat, runny nose and cough. Headache and body aches are commonly present. There may also be difficulty in breathing, increased heart rate, vomiting and diarrhea. Symptoms may go away on their own eventually within 3-7 days.

Diagnosis

Diagnosis is made based on clinical findings. Some laboratory tests may be performed to confirm the diagnosis. In case of complications such as pneumonia, a more through series of tests will be required.

Treatment

Treatment is not necessary as symptoms often resolve by themselves. Bed rest and fluids help speed up recovery. Some antiviral drugs may be used if needed along with painkillers to relieve headaches and muscle pain.

References

Article

  1. Eccles R. Understanding the symptoms of the common cold and influenza. Lancet Infect Dis 5 (11): 718–25, 2005. 
  2. Bischoff WE, Reid T, Russell GB, Peters TR. Transocular entry of seasonal influenza-attenuated virus aerosols and the efficacy of n95 respirators, surgical masks, and eye protection in humans. J Infect Dis 2011; 204:193.
  3. Mubareka S, Lowen AC, Steel J, et al. Transmission of influenza virus via aerosols and fomites in the guinea pig model. J Infect Dis 2009; 199:858. 
  4. Lozano R. Global and regional mortality from 235 causes of death for 20 age groups in 1990 and 2010: a systematic analysis for the Global Burden of Disease Study 2010. Lancet 380 (9859): 2095–128, 2012
  5. Drake JW. Rates of spontaneous mutation among RNA viruses. Proc Natl Acad Sci U S A. May 1 1993;90(9):4171-5.
  6. Hilleman M. Realities and enigmas of human viral influenza: pathogenesis, epidemiology and control. Vaccine. Aug 2002. 20 (25–26): 3068–87. 
  7. Warren L. Review of Medical Microbiology and Immunology. 11th ed. Pa: McGraw Hill, 2010. ISBN 978-0-07-170028-3. 
  8. Lam J, Nikhanj J, Ngab T, et al. Severe Cases of Pandemic H1N1 Pneumonia and Respiratory Failure Requiring Intensive Care. J Intensive Care Med. 5;26:318-25.
  9. Fiore AE, Fry A, Shay D, et al. Antiviral agents for the treatment and chemoprophylaxis of influenza --- recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep 2011; 60:1. 
  10. Grohskopf LA, Olsen SJ, Sokolow LZ, et al. Prevention and control of seasonal influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices (ACIP) -- United States, 2014-15 influenza season. MMWR Morb Mortal Wkly Rep 2014; 63:691.

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