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Relating to, marked by, or resulting from influenza.
Farlex Partner Medical Dictionary © Farlex 2012


Relating to, marked by, or resulting from influenza.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012


(in?floo-en'za) [Italian influenza, influence (of the stars)]
An acute contagious respiratory infection marked by fevers, chills, muscle aches, headache, prostration, runny nose. watering eyes, cough, and sore throat. The disease usually strikes during the winter. In patients with serious pre-existing illnesses (such as diabetes, chronic obstructive lung disease, heart disease or renal failure) and people over 65, influenza frequently is fatal. The disease spreads primarily by inhalation of infectious aerosols, although spread by direct personal contact also is possible. Epidemics or pandemics arise intermittently around the world during periods of viral evolution; in the winter of 1918 to 1919, an influenza pandemic claimed 20 million victims. Sporadic cases occur each year in the U.S., where the disease is responsible for an average of 36,000 deaths annually. Synonym: flu; grippecold; influenzal (-zal), adjective


The responsible virus is either influenza A (about 65% of cases) or influenza B (about 35% of cases). A negligible number of infections are caused by influenza C.


The incubation period of influenza is about 1 to 3 days, and the acute course of the illness typically lasts less than a week. Bacterial superinfection may occur, causing secondary pneumonias, sinusitis, or otitis media. Many patients lack energy and feel fatigued during their recuperation from acute infection.


The classification and naming of Influenza viruses depends on several elements—the nucleoprotein of the virus; the geographic location from which it is first isolated, its surface antigens, the year when it was first isolated in a laboratory, the adaptation of the virus to animals other than humans (such as birds, pigs, or horses), and its strain number.

Whether an influenza virus is called influenza A or influenza B depends on its nucleoprotein. This is a protein within the nucleus of the virus, that packages the viral ribonucleic acid (RNA) and helps transcribe its genetic contents.

The location where the virus is first identified (the viral geographic source) is usually the name of a city, state, or country, e.g. Stockholm, Texas, Panama.

If the virus was first identified as a cause of disease in 2009, it is a 2009 virus. This identifier is the viral year.

The next feature in the naming system is linked to the two proteins that the virus uses to enter into and explode out of infected cells in the respiratory tract. These proteins are called hemagglutinin and neuraminidase, respectively; and are abbreviated H and N (or HA and NA). Fifteen hemagglutinins have been identified. Most of these infect water fowl, e.g., geese and ducks. Three of them are known to infect people. Several of them can infect both birds and people (and other animals like swine).

When an animal cell is infected with more than one influenza virus at the same time, reassortment of viral genes can occur, and new viruses with new mixtures of disease-causing proteins can emerge. The influenza virus has eight major components, and pieces of one virus may link with pieces of others to form novel, and occasionally deadly combinations. A virus that emerges from a pig (after it has been infected with an avian virus and a human virus) with parts that are mostly found in pigs is called a swine flu virus. Similarly, a virus that mutates on its own within a pig and becomes infectious to people is also called a swine flu virus.

Newly mutated and reassorted viruses appear fairly frequently around the world every year, and are carried (by migrating birds) rapidly from one place to another. People can also carry influenza viruses rapidly around the globe if they travel when they are actively infected.

Public health data clearly have shown that about 30,000 people die of infection with influenza each year.


Worldwide surveillance for new influenza antigens is an ongoing public health project; each year, updated vaccines are developed to counteract new strains of the disease. In the U.S., about 70 million people are vaccinated each year. Vaccination is offered in the late autumn, prior to the start of flu season. The trivalent vaccine offered is based on the previous year’s virus. Vaccination should be offered to people over 65 and individuals with underlying cardiac, pulmonary, renal, or hepatic disease, cancer, diabetes mellitus, and other chronic or debilitating illness, as well as all health care professionals. Vaccination of the general population prevents epidemic disease and prevents significant economic losses caused by employee absenteeism. Influenza vaccines are more than 70% effective in older adults and about 90% effective in younger recipients.

Vaccination in Pregnancy

Women in the second and third trimesters of pregnancy are among the target groups for immunization: they, more than other members of the general population, should be recruited to receive influenza vaccination. Pregnant women with underlying heart, lung, or other chronic illnesses (such as diabetes mellitus) should receive influenza vaccination at any stage of pregnancy.

Recipients must be asked about hypersensitivity to eggs and egg products because the vaccine is made from chick embryos and must not be given to anyone with such allergies. Recipients also should be advised about possible adverse effects of the vaccine: local discomfort, low-grade fever, malaise, and the rare complication of Guillain-Barré syndrome, a form of ascending flaccid paralysis.


Children with influenza-like illnesses should avoid aspirin products because of the risk of Reye syndrome. All patients receiving influenza vaccines should review federally mandated Vaccine Information Sheets carefully before getting their injections.


Influenza A virus is treatable with antiviral drugs. These agents have an impact on the duration of infection with either influenza A or B virus. Symptom-based treatment with acetaminophen, NSAIDs, cough remedies (such as dextromethorphan, an antitussive or guaifenesin, an expectorant), and other over-the-counter remedies alleviate some of the misery the illness causes.

Patient care

Warm shower, baths, or heating pads help to relieve myalgias. All hospitalized patients should be protected from visitors who may have the flu (during flu season), and health care personnel should not provide patient care if they are ill or feel as if they may be coming down with flu. For the hospitalized patient, respiratory and blood and body fluid precautions are followed. Vital signs and fluid balance are monitored. Respiratory function is assessed for signs and symptoms of developing pneumonia, such as inspiratory crackles, increased fever, pleuritic chest pain, dyspnea, and coughing accompanied by purulent or bloody sputum. Prescribed analgesics, antipyretics, and decongestants are administered. Bedrest and increased oral fluid intake are encouraged, and intravenous fluids administered if prescribed. Oxygen therapy is administered if necessary. The patient is assisted to return to normal activities gradually. Nonalcoholic mouthwash or warm saline gargles are provided to ease throat soreness. The patient is taught proper cough etiquette and thorough hand hygiene to prevent spread of the virus. The patient treated at home is taught about all of the above supportive care measures as well as about signs and symptoms of serious complications to be reported.

Asian influenza

Influenza caused by a variant strain of influenza virus type A.

avian influenza

Abbreviation: AI
One of several influenza A viruses that primarily infects birds and poultry, and may occasionally cause a febrile illness in human beings. Symptoms in people include cough, muscle aches, sore throat and headache. Severe cases may cause viral pneumonia or acute respiratory distress syndrome. A pandemic of avian influenza (type H5N1) in the early 20th century killed millions of people worldwide.
Synonym: bird flu

highly pathogenic avian influenza

Abbreviation: HPAI
Any genetic variant of avian influenza A that causes serious illness, or carries a high probability of death, in infected birds.

low pathogenic avian influenza

Abbreviation: LPAI
Any genetic subtype of avian influenza A that causes mild, nonfatal disease in infected birds.

swine influenza

Any of several influenza A viruses that primarily infects cells that line the respiratory tracts of pigs. It can spread to humans or birds when a pig is infected with more than one strain of influenza at the same time and the nucleic acids from the separate species mix, forming a new, potentially dangerous combination. Synonym: swine flu
Medical Dictionary, © 2009 Farlex and Partners
References in periodicals archive ?
Deaths during the years 1918-1920 were recorded for 1,229 individuals who died from influenzal illnesses and 825 individuals who died from pneumonia and related illnesses.
Influenzal encephalopathy and postinfluenzal encephalitis.
In the LRTI category, we included acute bronchitis and bronchiolitis, acute lower respiratory infections NOS, chest infections NOS, laryngotracheobronchitis, tracheobronchitis, bacterial and viral pneumonia, bronchopneumonia, influenzal pneumonia, and pneumonitis.
The investigators noted that an estimated 500,000 neurologic deaths following the 1918 influenza pandemic were be-lieved to be caused by postinfectious influenzal encephalopathy, although they conceded that "the association remains controversial."
50 YEARS AGO: The Queen is suffering from an influenzal cold and is remaining in her rooms at Buckingham Palace for the present.