Influenza is an acute viral respiratory infection caused by RNA–containing influenza A, B and C viruses, manifested by fever, intoxication and damage to the epithelial lining of the upper respiratory tract. Influenza is included in the group of acute respiratory viral infections – ARVI. The greatest infectious danger of a person with influenza is in the first 5-6 days from the onset of the disease. The way of transmission of influenza is aerosol. The duration of the disease, as a rule, does not exceed a week. However, with the flu, complications such as otitis, sinusitis, pneumonia, cystitis, myositis, pericarditis, hemorrhagic syndrome can be observed. Flu is especially dangerous for pregnant women, because it can lead to the threat of termination of pregnancy..
Influenza virus belongs to the genus Influenzavirus, type A virus can infect humans and some animals, types B and C reproduce only in the human body. Influenza viruses are characterized by high antigenic variability (highly developed in viruses of type A and b, less in C). Antigenic polymorphism contributes to frequent epidemics, multiple morbidity during the season, and also does not allow developing a sufficiently reliable group-specific prevention. The flu virus is unstable, easily dies when the temperature rises to 50-60 degrees, under the influence of chemical disinfectants. At 4 ° C, it can remain viable for up to 2-3 weeks.
The reservoir and source of infection is a sick person (with obvious clinical manifestations or an erased form of infection). The maximum release of the virus takes place in the first 5-6 days of the disease, the contagiousness depends on the severity of catarrhal symptoms and the concentration of the virus in the secret of the mucous membrane of the respiratory tract. The influenza A virus is also isolated from sick pigs, horses and birds. One of the modern theories suggests that migratory birds play a certain role in the spread of the influenza virus on a global scale, mammalian animals serve as a reservoir of infection and contribute to the formation of new strains that can subsequently infect humans.
The mechanism of transmission of influenza is aerosol, the virus is spread by airborne droplets. The discharge occurs with saliva and sputum (when coughing, sneezing, talking), which in the form of a fine aerosol spreads in the air and is inhaled by other people. In some cases, it is possible to implement a contact-household transmission path (mainly through dishes, toys).
The natural susceptibility of humans to the influenza virus is high, especially with respect to new serotypes. Immunity is type–specific, its duration reaches 1-3 years with influenza type A, type B – 3-4 years. Breastfed children receive antibodies from their mother, but often this immunity does not protect against the development of infection. The prevalence of the flu virus is ubiquitous, epidemics regularly break out, often on a global scale.
The incubation period of influenza usually ranges from several hours to three days, the onset is mainly acute, the course can be mild, moderate, severe, with or without complications. The clinical picture of influenza is represented by three main symptom complexes: intoxication, catarrh and hemorrhage.
The development of intoxication syndrome begins from the first hours of the disease, body temperature can rise up to 40 degrees, chills, headache and dizziness, general weakness are noted. There may be moderate myalgia and arthralgia, convulsions, disorders of consciousness. The intensity of the intoxication syndrome determines the severity of the course of uncomplicated influenza and can vary very widely, from moderate malaise to intense feverish reaction, vomiting of a central nature, convulsions, confusion and delirium.
Fever often occurs in two waves, the symptoms usually begin to subside by the 5-7 day of the disease. When examined during the febrile period, hyperemia of the face, hyperthermia and dry skin are noted, tachycardia is detected, there may be some decrease in blood pressure. Catarrhal symptoms manifest themselves shortly after the development of intoxication (sometimes expressed weakly or may be absent altogether). Patients complain of dry cough, discomfort and soreness in the throat and nasopharynx, runny nose. The clinic of laryngitis and bronchitis may manifest itself: hoarseness of the voice, soreness behind the sternum with a dry, increasing intensity, strained cough. On examination, sometimes there is a slight hyperemia of the pharynx and the posterior wall of the pharynx, tachypnea.
In 5-10% of cases, the flu can contribute to the development of hemorrhagic symptoms. At the same time, catarrhal phenomena are joined by small hemorrhages in the mucous membrane of the oropharynx, nosebleeds. With the development of severe hemorrhage, its progression to acute pulmonary edema is possible. Influenza is usually not accompanied by symptoms from the abdominal cavity and pelvic organs, if such a clinic takes place, then it is predominantly neurogenic in nature.
Intestinal disorders with influenza in young children are associated with intoxication syndrome. Diarrhea with influenza in adults, most likely, indicates the presence of chronic diseases of the digestive system, provoked to exacerbation by infection. The duration of the flu on average does not exceed 3-5 days, in the future, sometimes general asthenia persists for several days. There have been cases of atypical flu, mild, erased forms, as well as infection combined with other viruses.
Influenza can be complicated by a variety of pathologies both in the early period (usually caused by a bacterial infection that has joined) and later. Severe complicated course of influenza is usually found in young children, elderly and weakened persons suffering from chronic diseases of various organs.
Quite rarely, with extremely severe intoxication, the flu is complicated by a severe, life–threatening condition – acute hemorrhagic pulmonary edema. At the same time, there is a sharp increase in breathing difficulties, and cyanosis, bloody foamy sputum is released. The result of acute hemorrhagic pulmonary edema is progressive respiratory failure and hypoxic coma, often leading to death.
The addition of infection during the course of the flu most often contributes to the development of pneumonia, the lungs are mainly affected by streptococcal and staphylococcal flora, pneumonia of this etiology proceeds with a tendency to destruction of lung tissue, may be complicated by pulmonary bleeding, edema, provoke infectious and toxic shock. After pneumonia, residual phenomena often persist in the form of bronchiectasis, pneumosclerosis.
Influenza can contribute to the development of otitis media, as well as be complicated by sinusitis, sinusitis, and frontitis. From other organs and systems, nephritis, pyelocystitis, myositis, inflammation of the heart sac (pericarditis) may be noted. Complications from the heart in influenza are considered to be the cause of an increase in the frequency of myocardial infarctions during the epidemic, the development of acute cardiovascular insufficiency. In pregnant women, the flu can cause miscarriage or stillbirth.
Preliminary diagnosis is carried out on the basis of the clinical picture and the data of the rapid diagnosis of RNIF or ELISA (detection of influenza virus antigen in smears taken in the nasal cavity), serological diagnostic methods serve as confirmation of the diagnosis: the increase in the titer of antibodies is determined using RTGA, RSC, RNGA, ELISA. The diagnostic value has more than a fourfold increase.
If pneumonia is suspected, a patient with influenza may need to consult a pulmonologist and perform a lung radiography. With the development of complications from the ENT organs, an otolaryngologist examination with otolaryngology and rhinoscopy is necessary.
Influenza is treated mainly on an outpatient basis, hospitalizing only patients with severe and complicated forms of infection. In addition, children from orphanages and boarding schools are subject to hospitalization.
For the period of fever, patients are recommended bed rest, copious drinking, a balanced full-fledged diet, vitamins. As a means of etiotropic therapy in the first days of the disease, remantadine is prescribed (it has contraindications: age up to 14 years, pregnancy and lactation, kidney and liver pathology), oseltamivir. Late administration of antiviral drugs is ineffective. The appointment of interferons may be recommended. In addition to antiviral therapy, vitamin C, calcium gluconate, rutin, antipyretics, antihistamines are prescribed.
A severe course of influenza often requires detoxification measures (parenteral infusion of hemodesis solutions, rheopolyglucine) with the forcing of diuresis. Euphyllin, ascorbic acid, and diphedrol are often added to detoxification solutions. With developing edema of the lungs or brain, the dosage of saluretics is increased, prednisone is prescribed intravenously, and the necessary intensive care measures are carried out. Developing cardiovascular insufficiency is an indication for the appointment of thiamine pyrophosphate, sulfocamphoric acid with procaine, potassium and magnesium preparations. At the same time, the necessary correction of internal acid-base homeostasis is performed, the patency of the respiratory tract is monitored.
Prognosis and prevention
Mainly, the prognosis of influenza infection is favorable, recovery occurs in 5-6 days. The deterioration of the prognosis causes a severe course in young children, the elderly, the development of life-threatening complications. The prognosis of pregnancy is unfavorable – the flu often provokes its termination.
Currently, measures have been developed for specific prevention of influenza, which is carried out against the most common strains. The multi-antigenic structure of influenza epidemics does not allow vaccination to completely eliminate the possibility of influenza, but the sensitized organism tolerates infection much easier, the risk of severe complications in immunized children is significantly reduced. It is advisable to vaccinate against influenza a few weeks before the predicted epidemic period. Influenza immunity is short–term, it is desirable to immunize every year.
General prevention during periods of mass epidemics includes the usual measures to prevent the spread of airborne infections. Personal prevention consists in avoiding contact with patients, crowded places, wearing a gauze mask covering the respiratory tract, preventive administration of antiviral drugs in case of a risk of infection, as well as measures aimed at strengthening the immune properties of the body.