What is the Flu?

Influenza is an acute respiratory disease of viral etiology that occurs with symptoms of general intoxication and respiratory tract damage. It refers to airborne anthroponoses.

Flu is currently the most common infectious disease. In a short time covers huge masses of the population. An increase in the incidence associated with the most virulent and contagious virus A is recorded annually. Once every 3-4 years, there is an increase in the number of patients with influenza B. The influenza C virus causes sporadic diseases or outbreaks in children’s groups. Susceptibility to influenza appears to be absolute. It is believed that a person has a weak immune response gene for influenza and influenza-like diseases. Due to the type-specific immunity, the emergence of new mutant forms of the virus leads to the overcoming of collective immunity, developed after a previous flu epidemic.

The most susceptible to influenza and other forms of SARS are individuals with signs of a secondary immunodeficiency state. Hypothermia, negative stressful situations, nervous shocks, emotional and physical overloads, alcohol abuse, work in the microwave field lead to the development of immunodeficiency.

Seasonality: from November to March, as the flu virus is better preserved at moderately low temperatures and high humidity.

Causes of Flu

Until 1933, the wand of Afanasyev-Pfeiffer was considered the causative agent of the flu. The viral nature of influenza was established in 1933 in England by Smith, Andrews and Laydlow, who isolated a specific pneumotropic virus from lung hamsters infected with nasopharyngeal swabs of patients with influenza and designated them as influenza A virus. In 1940, Francis and Magil discovered the influenza virus In, and in 1947, Taylor identified another new version of the influenza virus – type C.

Influenza viruses of types B and C practically do not change their antigenic structure, whereas the type A influenza virus changes rapidly, forming new subtypes and antigenic variants. The antigenic structure of influenza A viruses has undergone significant changes. In 1946-1957 new variants of influenza A virus – A1 and A2 have been identified, and the viruses isolated in subsequent years differ significantly in antigenic properties from the influenza A2 virus.

Influenza viruses belong to the group of RNA-containing orthomyxoviruses with a particle size of 80-120 nm. Influenza viruses contain various antigens. S-antigen, or internal nucleocapsid includes ribonucleic acid and viral protein, accounting for 40% of the mass of the virion. The outer shell of the virion contains a surface V-antigen. In its structure hemagglutinin and neuraminidase.

A change in hemagglutinin or neuraminidase causes the appearance of new subtypes of the virus within type A. New antigenic variants of the virus cause more severe and more widespread influenza epidemics.

According to the modern nomenclature of the influenza A type virus, adopted by WHO in 1980, the influenza viruses isolated from humans were found to have 3 subtypes of the H antigen (H 1, H2, N3) and 2 subtypes of the N antigen (N1 and N2). In accordance with this nomenclature, influenza viruses circulating in the population up to 1957 have the general antigen formula A (H 1N1), from 1957 to 1968 – A (H2N2), and since 1968 – A (H3N2).

Influenza viruses have a low resistance to physical and chemical factors and are destroyed at room temperature for several hours, while at low temperatures (from -25 ° C to -70 ° C) persist for several years. They die quickly when heated, dried, and when exposed to small concentrations of chlorine, ozone, and ultraviolet radiation.

The source of influenza infection is only a sick person with obvious and erased forms of the disease. The route of transmission is airborne. The maximum infectiousness is observed in the first days of the disease, when, when coughing and sneezing with droplets of mucus, the virus is released into the external environment. Virus isolation in an uncomplicated course of the flu ends by the 5th-6th day of the onset of the disease. At the same time, with pneumonia complicating the flu, the virus is detected in the body up to 2-3 weeks from the onset of the disease.

Increased incidence and outbreaks of flu occur during the cold season. Epidemics caused by the type A influenza virus recur every 2 to 3 years and are explosive in nature (20–50% of the population falls ill within 1–1.5 months). Epidemics of influenza B spread more slowly, lasting 2-3 months. and affect no more than 25% of the population.

Due to the fact that not all of the population suffers from the flu at the same time and the duration of immunity is different, a considerable non-immune stratum is periodically formed, especially susceptible to new, alien variants of the virus. Local strains of influenza viruses often cause only a seasonal increase in the incidence.

Pathogenesis during the Flu

The influenza virus selectively affects the epithelium of the respiratory tract (mainly the trachea). Multiplying in the cells of the cylindrical epithelium causes their degenerative changes, using the contents of the epithelial cells to build new viral particles. Massive release of mature viral particles is often accompanied by the death of epithelial cells, and necrosis of the epithelium and the associated destruction of the natural protective barrier leads to viremia. The toxins of the influenza virus, along with the decay products of epithelial cells, have a toxic effect on the cardiovascular, nervous (central and vegetative) and other systems of the body. Influenza infection leads to immunosuppression, and the introduction of secondary bacterial flora through the necrotic surface of the mucous membrane of the respiratory tract can cause various complications.

In the pathogenesis of influenza there are five main phases of the pathological process:

  • I – reproduction of the virus in the cells of the respiratory tract;
  • II – viremia, toxic and toxic-allergic reactions;
  • III – lesion of the airways with preferential localization of the process in any part of the respiratory tract;
  • IV – possible bacterial complications of the respiratory tract and other body systems;
  • V – reverse development of the pathological process.

Circulatory disorders, caused by impaired tone, elasticity and permeability of the vascular wall, especially the capillaries, play the leading role in the basis of the defeat of various organs and systems during the flu. Increased permeability of the vascular wall leads to impaired microcirculation and the occurrence of hemorrhagic syndrome (nosebleeds, hemoptysis, and in severe cases – hemorrhage into the substance and the lining of the brain, into the alveoli, which is manifested by the syndrome of infectious-toxic encephalopathy or hemorrhagic toxic lung edema).

Influenza causes a decrease in immunological reactivity. This leads to the exacerbation of various chronic diseases, as well as to the emergence of secondary bacterial complications. The most frequent and serious complication of influenza is acute pneumonia. It is now generally recognized that pneumonia in influenza is of mixed viral and bacterial nature, regardless of the timing of its occurrence.

The inflammatory process in the lungs may be due to the accession of various bacterial flora (often pneumococci), but in recent years, Staphylococcus aureus has become increasingly important.

Flu Symptoms

The incubation period lasts from 12 to 48 hours. The following clinical forms of the disease are distinguished: typical influenza and atypical (afebrile, akatoralny and fulminant); by severity – mild, moderate, severe and very severe flu; by the presence of complications – complicated and uncomplicated influenza.

Typical flu begins acutely, in most cases with chills or chills. The body temperature in the first day reaches the maximum level (38 -40 ° C). The clinical picture is manifested by a syndrome of general toxicity and signs of pores in the respiratory tract. Simultaneously with fever, general weakness, fatigue, weakness, excessive sweating, muscle pain, severe headache with a characteristic localization in the frontal region and superciliary arches appear. Appear pain in the eyeballs, aggravated by the movement of the eyes or when pressed on them, photophobia, lacrimation.

The defeat of the respiratory tract is characterized by the appearance of sore throat, dry cough, nagging pain behind the sternum (along the trachea), nasal congestion, hoarse voice.

An objective examination marked hyperemia of the face and neck, vascular injection of the sclera, moist luster of the eyes, increased sweating. In the future, you may receive a herpetic rash on the lips and near the nose. There is a hyperemia and a peculiar granularity of the mucous membrane of the pharynx. On the part of the respiratory organs, signs of rhinitis, pharyngitis, and laryngitis are detected. Particularly characteristic is the defeat of the trachea, more pronounced compared with other parts of the respiratory tract. Bronchitis occurs much less frequently, and damage to the lungs (the so-called influenza pneumonia) is considered as a complication. In addition to the general toxic symptoms, disease-specific meningeal symptoms (stiff neck, Kernig, Brudzinsky symptoms) may appear at the height of the disease, which disappear after 1 -2 days. In the cerebrospinal fluid pathological changes are not detected. The blood picture with uncomplicated influenza is characterized by leukopenia or normocytosis, neutropenia, eosinopenia, and relative lympho-monocytosis. ESR is not increased.

Depending on the level of intoxication and the severity of catarrhal syndrome, influenza can occur in mild, moderate, severe and very severe form.

A mild form of influenza is characterized by an increase in body temperature of not more than 38 ° C, moderate headache and catarrhal symptoms. Pulse less than 90 beats / min. Systolic blood pressure 115-120 mm Hg. Art. Respiratory rate less than 24 in 1 min.

With moderate form of influenza – body temperature in the range of 38.1-40 ° C. Moderately expressed intoxication syndrome. Pulse 90-120 beats / min. Systolic blood pressure less than 110 mm Hg. Art. Respiratory rate more than 24 in 1 min. Dry, painful cough with pain behind the sternum.

Severe flu is characterized by an acute onset, high (over 40 °) and its long fever with pronounced symptoms of intoxication (severe headache, aching all over, insomnia, delirium, anorexia, nausea, vomiting, meningeal symptoms, and sometimes encephalitic syndrome) . Pulse more than 120 beats / min, weak filling, often arrhythmic. Systolic blood pressure less than 90 mm Hg. Art. Heart sounds are deaf. Respiratory rate more than 28 in 1 min. Painful, painful cough, pain behind the sternum.

Very severe forms of influenza are rare, characterized by fulminant with rapidly developing symptoms of intoxication, without catarrhal phenomena and end in most cases lethal. A variant of the lightning form can be the rapid development of hemorrhagic toxic pulmonary edema and the sad outcome from parenchymal respiratory and cardiovascular insufficiency in the event of late provision of emergency and specialized medical care.

During epidemic outbreaks, the flu is more severe with the prevalence of typical forms of the disease. In interepidemic time, light and atypical forms of influenza are more often observed, when intoxication symptoms are mild, and the body temperature either remains normal (afebrile form of influenza), or rises no more than 38 ° C. In the clinical picture of the disease to the fore the symptoms of rhinitis, pharyngitis. If the inflammatory process is localized in the trachea with a visible absence of rhinitis and pharyngitis, then we are talking about the so-called acatal form of flu.

Influenza in children

Influenza in children differs from the disease in adults in a more severe course of the process, more frequent development of complications, reduces the reactivity of the child’s body and aggravates the course of other diseases. Disruption of the general condition, febrile reaction and lesions of the upper respiratory tract are more pronounced and prolonged, often reaching 5-8 days.

People of all ages are susceptible to the flu, from baby to deep old man. Persons 60 years and older suffer from the flu more severely than young people. The specific features of the course of influenza in elderly and senile patients are longer periods of time throughout the course of the disease, a more severe course with frequent complications. Persons of this age group have a more gradual development of the disease and they have cardiovascular disorders (shortness of breath, cyanosis of the nasolabial triangle and mucous membranes, acrocyanosis against the background of tachycardia and a sharp decrease in blood pressure). The phenomena of general intoxication in them are less pronounced and in the clinical picture recede into the background. The duration of the febrile period reaches 8 -9 days, the temperature decreases slowly, remaining subfebrile for a long time.

The duration of the illness with uncomplicated influenza in general in elderly people is 1.5 times longer compared with young patients and is 1-1.5 weeks. Influenza in the elderly and the elderly is complicated by pneumonia 2 times more often than in young and middle-aged people.


With no infectious disease, early detection of complications does not represent as many diagnostic difficulties as with the flu. Complications of influenza infection are very frequent (10 -15% of all cases of influenza). In their clinical diversity, the leading position (80 -90%) is occupied by acute viral-bacterial pneumonia, which were detected up to 10% of all patients and about half of the hospitalized patients with influenza, mainly severe and moderate forms. The second most common place is occupied by complications of the ENT organs (sinusitis, otitis, frontitis, sinusitis); less often – pyelonephritis, pyelocystitis, cholangitis, etc.

Pneumonia, which complicates the course of the flu, can develop in any period of the disease, however, in young people, early pneumonia prevails in 60% of cases, occurring on days 1-5 of the onset of the disease, usually with marked catarrhal syndrome and general intoxication, which makes it much harder timely diagnosis of these complications.

In typical cases, the course of influenza complicated by pneumonia is characterized by prolonged fever (more than 5 days) or the occurrence of a second temperature wave after a short-term normalization of body temperature. During the course of the flu disease there is no positive dynamics in the patient’s state or well-being. Remains severe weakness, sweating, chills, shortness of breath. A cough joins with a purulent or bloody sputum. During auscultation, fine-bubbling moist rales, crepitus may be heard in the position of the patient on the affected side (Kuravitsky method) or after short coughing. The majority of patients in the blood – leukocytosis, increased ESR.

For the purpose of early diagnosis (prediction) of acute pneumonia in the very initial phase, before the formation of distinct clinical and radiological manifestations, it is recommended in the outpatient setting (for home treatment) to use a complex of clinical and laboratory indicators, including an increase in body temperature above 39 ° C, symptoms of tracheobronchitis , dyspnea more than 24 breaths per 1 min, leukocytosis more than 8 × 109 / l and ESR above mm / h. This complex was detected in 65% of patients with influenza with the subsequent development of pneumonia, confirmed radiographically. Identification of such a complex in patients with influenza provides the basis for transferring these patients to an infectious disease hospital and carrying out a poison with anti-influenza etiotropic and pathogenetic treatment of the antibiotic therapy cycle. In case of suspicion of complications on the part of ENT agencies, an otorhinolaryngologist consultation is indicated.

Diagnosis of Influenza

Diagnosis and differential diagnosis. Recognition of influenza during an epidemic outbreak is not difficult when its clinical manifestations are typical, and the proportion of influenza among all acute respiratory infections reaches 90%. In interepidemic time when atypical forms of influenza prevail, it is clinically difficult to differentiate it from other acute respiratory infections, since the share of influenza in this period accounts for 3-5% of the total number of acute respiratory infections.

At this time, the diagnosis of influenza can be made only after laboratory confirmation.

For rapid diagnosis of influenza using the rapid method of detecting influenza virus using fluorescent antibodies. The test material is taken from the nose in the first days of the disease. The smears prepared from it are treated with specific influenza fluorescent sera. The resulting antigen-antibody complex glows brightly in the nucleus and cytoplasm of the cells of the cylindrical epithelium and is clearly visible in the fluorescent microscope. The answer can be obtained in 2 to 3 hours.

Serological tests help retrospective diagnosis of influenza. Investigate paired serum taken from patients during the acute period of the disease (up to the 5th day from the onset of the disease) and during the recovery period with an interval of 12-14 days. The most indicative in serological diagnostics are the reaction of complement fixation (RSK) with influenza antigens and the reaction of hemagglutination inhibition (HI). Diagnostic is the increase in antibody titer 4 times or more.

Differential diagnosis of influenza should be carried out both with acute respiratory diseases and with a number of other infections, since the onset of many of them resembles the flu due to intoxication and catarrhal symptoms.

Influenza and other acute respiratory infections vary in localization of airway lesions and a number of clinical manifestations. With the flu, all parts of the respiratory tract suffer, but tracheitis prevails, manifested by dry cough and pain along the trachea. With parainfluenosis, the larynx is mainly affected and laryngitis occurs in the form of hoarseness and coarse strong cough. Adenovirus infection is manifested by lesions of the mucous membranes of the eyes, nose, throat, tonsils with the most pronounced changes in the pharynx. In rhinovirus infection, the leading symptoms of the disease are rhinitis and rhinorrhea.

With differential diagnosis with other frequently occurring infectious diseases, it must be remembered that in their initial period there may be a syndrome of general intoxication and catarrhal syndrome, which, however, have no relation to the flu. Thus, when measles is accompanied by severe intoxication, the respiratory tract is always affected (rhinitis, pharyngitis, laryngitis, tracheitis, and sometimes bronchitis). However, a number of signs (conjunctivitis, and especially Filatov-Belsky-Koplik spots on the cheek mucosa) allow diagnosing measles before the appearance of a characteristic measles exanthema.

Inflammatory changes in the upper respiratory tract, along with fever and general intoxication, are a characteristic manifestation of the catarrhal (influenza-like) variant of the initial (pre-Alert) period of viral hepatitis.

From the group of typhoid paratyphoid diseases, differential diagnosis should be performed with paratyphoid A. In the initial period of this disease, catarrhal syndrome often occurs (rhinopharyngitis, tracheobronchitis, conjunctivitis). But unlike the flu, paratyphoid A begins gradually, with each day the height of the fever increases, and the pronounced effects of the general intoxication syndrome do not correspond to mild inflammatory changes in the respiratory tract. Fever of the permanent type, and the appearance on the 4th-7th day of illness of a polymorphic rash exclude the likelihood of influenza.

For meningococcal infection, its localized form – nasopharyngitis is characterized by moderate manifestations of general intoxication, sore throat, sore throat, runny nose, difficulty in nasal breathing. When viewed from – bright hyperemia and swelling of the mucous membrane of the posterior pharyngeal wall, the nasal mucosa. In the blood – leukocytosis with a neutrophilic shift to the left, increased ESR. Signs of meningism are possible. Constant observation of this kind of patients, repeated examination of blood and cerebrospinal fluid in the dynamics allow us to exclude the flu or to diagnose the transition to a generalized form of meningococcal infection.

Influenza Treatment

Treatment for influenza is used a complex of etiotropic, pathogenetic and symptomatic agents aimed at the causative agent of the disease, detoxification of the body, increase of protective forces, elimination of inflammatory and other changes.

Treatment of mild and moderate forms of influenza is carried out at home, severe and complicated – in an infectious diseases hospital. During the febrile period, the patient with influenza needs bed rest, warmth, and abundant hot drinking with a large amount of vitamins, especially C and P (tea, compote, dogrose infusion, fruit juices, fruit drink, 5% glucose solution with ascorbic acid). For the prevention of hemorrhagic complications, especially older people with elevated blood pressure, green tea, jam or chokeberry juice (aronia), grapefruits, and vitamins of group P (rutin, quercetin) in combination with 300 mg of ascorbic acid per day are needed.

To reduce severe headache and muscle pain, shorten toxicosis and inflammatory changes in the airways, use the complex preparation “anti-influenza” (acetylsalicylic acid 0.5; ascorbic acid 0.3; calcium lactate 0.1 g; rutin and dimedrol 0.02 d) within 3-5 days, 1 powder 3 times a day. You can also use coldrex or aspirin oops with vitamin C, after having dissolved the pill of these drugs in warm water half a glass, or analgesics-amidopirin, panadol, tempalgin, with edalgin 1 tablet 2-3 times a day. Antipyretics (acetylsalicylic acid more than 0.5 times) should be taken only at high body temperature, reaching 39 ° C or more and 38 ° C in children and the elderly.

It is necessary to prescribe a complex of vitamins, ascorbic acid, up to 600-800 mg / day, and strengthening the blood vessels of vitamin P, up to 150 -300 mg / day.

The antiviral drug rimantadine is effective in the treatment of influenza caused by the type A virus, and only with its early use – in the first hours and days of the onset of the disease (0.05 g 3 times a day for 3-4 days).

To improve the drainage function of the bronchi and enhance the evacuation of mucus and sputum, it is necessary to conduct warm, wet inhalations containing soda and bronchodilators (solutan, aminophylline, ephedrine).

Inhalations are carried out up to 15 minutes 2 times a day for 4 days. In case of pronounced rhinitis, a 2–5% solution of ephedrine, a 0.1% solution (or emulsion) of sanorin, naphthyzinum, and galazolin are used for and entranasal administration. The prescription of antibiotics or sulfonamides for the prevention of complications (pneumonia) in patients with uncomplicated influenza is unjustified, since it often contributes to the development of these complications.

Complex treatment of patients with severe forms of influenza, in addition to pathogenetic and symptomatic, includes specific etiotropic therapy. The most effective anti-influenza donor immunoglobulin (gamma -globulin), administered in the early stages of the disease at 3-6 ml intramuscularly with an interval of 8 -12 hours (children – 0.15-0.2 ml per 1 kg of body weight per day) to obtain pronounced therapeutic effect.

Pathogenetic detoxification therapy is enhanced by intravenous administration of neocompensan (hemodez) 200-300 ml, reopolyglukine 400 ml, 5% glucose solutions with ascorbic acid, Ringerlaktivat (lactasol) – up to 1.5 l / day against the background of forced diuresis using 1% solution of lasix (furosemide) 2-4 ml to avoid pulmonary and brain edema.

For very severe forms of influenza with severe toxic manifestations, corticosteroid preparations are prescribed – prednisone 90-120 mg / day or equivalent doses of other glucocorticoids, 10,000-20000 IU contrikala, as well as cardiac medications (0.06% corglycon solution 1 ml or 0.05% solution of strophanthin K 1 ml intravenously, in a drip). Oxygen therapy is performed with moistened oxygen through nasal catheters. With an increase in respiration of more than 40 in 1 min with violations of the respiratory rhythm of patients transferred to artificial respiration.

In extremely severe forms of influenza, anti-staphylococcal antibiotics are indicated (oxacillin, methicillin, cephalosporins in injections of 1.0 four times a day).

Prevention of Influenza

Prevention is reduced to isolating patients at home or in hospital and restricting sick visits to clinics and pharmacies. Servicing patients should wear 4–6 ply gauze masks and use intranasal 0.25–0.5% oxolinic ointment.

Vaccine prevention

For vaccine prophylaxis, inactivated influenza vaccines are used intracutaneously and under the skin. Chemoprophylaxis of influenza A is carried out by taking rimantadine (at 0.1 g / day), which is given throughout the outbreak. In the outbreak carry out the current and final disinfection.


With uncomplicated flu, work capacity is restored after 7 -10 days, with the accession of pneumonia – no earlier than 3-4 weeks. Severe forms (with encephalopathy or pulmonary edema) can be life threatening. Soldiers are discharged after clinical recovery, normal blood and urine tests not earlier than the 4th day of normal body temperature with release from work for 3 days. After transferring severe forms of influenza complicated by pneumonia, patients are referred for IHC to provide sick leave for up to 1 month.

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