Flu

Influenza (Grippus, Influenza) is an acute infectious disease with an aerosol transmitting mechanism of the pathogen, characterized by a massive spread, short-term fever, intoxication and airway disease, and a high incidence of complications.

Influenza is a specific acute respiratory viral disease of the respiratory tract with a high fever, runny nose, cough, headache, malaise. It occurs mainly in the form of epidemics in the winter. A lethal outcome is possible during epidemics, especially among high-risk patients (for example, in organized groups, in old age, with pulmonary heart failure, in late pregnancy). In severe cases, severe weakness, hemorrhagic bronchitis, pneumonia. Flu is usually diagnosed clinically. To prevent the flu can be through an annual vaccination. It is received by patients who have a high risk of disease, medical personnel, people with a large number of contacts, children from 6 to 24 months. Influenza A and B types are treated with zanamivir (neuraminidase inhibitor) and acetamivir; Flu A is treated with amantadine and remantadine.

ICD-10 code

• J10. Influenza caused by an identified influenza virus.
  • J10.0. Influenza with pneumonia, influenza virus identified.
  • J10.1. Influenza with other respiratory manifestations, the influenza virus is identified.
  • J10.8. Influenza with other manifestations, the influenza virus is identified.
• J11. Flu, the virus is not identified.
  • J11.0. Influenza with pneumonia, the virus is not identified.
  • J11.1. Influenza with other respiratory manifestations, the virus is not identified.
  • J11.8. Influenza with other manifestations, the virus is not identified.

Influenza: Epidemiology

Every year at the end of autumn - early winter, the flu virus causes sporadic morbidity. Large epidemics in the United States occur approximately every 2-3 years. The influenza A virus causes flu-like flu. The influenza B virus causes mild flu. But it can be the cause of epidemics with a 3-5-year cycle. Usually an epidemic is caused by a single serotype, although there may be different viruses in one region and cause morbidity simultaneously or alternate; and one can dominate.

Seasonal flu often has two waves: the first in school children and those who contact them (usually young people), and the second - in individuals from closed collectives and permanently in the house (especially the elderly).

The flu spreads from person to person by airborne droplets (the most significant route); In addition, virus-containing droplets can settle on objects and also cause infection.

Flu is severe in people with cardiopulmonary diseases, metabolic diseases (diabetes mellitus), requiring constant medical supervision, kidney failure, hemoglobinopathies and immunodeficiency. Also, severe influenza with fatalities occurs in pregnant women in the 2nd and 3rd trimesters, young children (less than 24 months), elderly (over 65 years) and bedridden patients.

What causes the flu?

Influenza is a disease that is caused by the influenza virus, and the use of this term for diseases caused by other respiratory viruses is not legal. Influenza viruses are classified according to nucleoproteins and protein matrix into types A, B and C. The influenza C virus does not cause a typical flu and is not discussed here.

Nucleocapsid is coated with a membrane containing two main glycoproteins, one of which has haemagglutinin (HA) activity and the other with neuraminidase enzymatic activity (NA). Hemagglutinin allows the virus to contact the cell. The virus is absorbed by the cell by endocytosis, its membrane merges with the endosome membrane, and the genetic material is released into the cytoplasm. Within the cell, replication takes place, and new virions are collected from the resulting viral components on the cell surface, which are budded with the participation of viral neuraminidase (removes sialic acids from the surface of the host cell). Small mutations in these agglutinins lead to a high incidence of the formation of new viral serotypes (antigenic drift). A consequence of this is a decrease in the protective effect of antibodies that were formed upon contact with previous serotypes. In contrast to antigenic drift, large mutations of influenza A glycoproteins (antigenic shift) are longer (10-40 years over the last 100 years); thus, there is no immunity to the new virus in the population, which is the cause of pandemics.

What symptoms does the flu have?

The flu has an incubation period of 1-4 days (an average of 48 hours). In mild cases, the symptoms resemble the symptoms of a cold (a throat, a runny nose), mild conjunctivitis. The flu begins suddenly with the appearance of chills and a fever of 39-39,5 C, there is a sharp weakness and generalized pains (most pronounced in the back and legs). But especially the patient is concerned with a headache, often combined with photophobia and retrobulbar pains. In the beginning, the flu symptoms from the airway may not be expressed, limited to a sore throat, burning behind the sternum, a dry cough and sometimes a runny nose. Later, influenza symptoms reflecting the defeat of the lower respiratory tract become prevalent; cough intensifies and turns into productive. Children have nausea and vomiting. Usually after 2-3 days acute symptoms of influenza disappear and the temperature drops, but it can last up to 5 days without complications. Usually, bronchio-ciliary drainage and bronchiolar resistance are disturbed. Weakness, sweating and fatigue do not last several days, sometimes weeks.

Pneumonia is indicated by shortness of breath, the appearance of purulent or bloody sputum, cyanosis, hemoptysis, wheezing and a secondary increase in temperature or relapse.

Sometimes, usually during the recovery period, the flu can be complicated by diseases such as encephalitis, myocarditis and myoglobinuria. The causes are not clear, but such complications are often given by influenza A. Reye's syndrome, characterized by encephalopathy, fatty hepatosis, hypoglycemia and lipidemia, is associated with the epidemic of influenza A, especially in children taking aspirin.

How is the flu diagnosed?

The flu is diagnosed on the basis of a clinical picture of the disease and epidemiological situation in the community. Although many diagnostic tests are available, their sensitivity and specificity vary widely in different studies. The use of such tests in a separate group of patients gave conflicting results. Specify the diagnosis of "influenza" allows the cell culture to scrape from the nasopharynx and determine the titer of antibodies in paired sera. These tests require 2 days or more and are needed to assess the epidemic situation and determine the serotype of the virus.

In the detection of lower respiratory tract symptoms, such as dyspnoea, hypoxia, wheezing in the lungs, X-rays are performed to exclude pneumonia, which often accompanies the flu. A typical primary influenza pneumonia is detected as diffuse interstitial infiltrates or manifests as an acute respiratory distress syndrome. Secondary bacterial pneumonia is more often focal or lobar.

How is the flu treated?

Uncomplicated influenza usually ends in recovery, although it may take 1-2 weeks. In some patients, especially from these high-risk groups, viral pneumonia and other complications can lead to death. Antiviral treatment of influenza in these cases is unknown. Specific antimicrobial chemotherapy reduces mortality from severe secondary pneumonia.

In most cases, the flu is treated symptomatically, bed rest and rest, copious drink, antipyretic drugs are shown, but in children, aspirin should be avoided.

Antiviral drugs prescribed within 1-2 days from the onset of symptoms, can reduce their duration. Influenza is also treated with antiviral drugs, which are recommended for patients from high-risk groups in those who develop flu-like symptoms, but there is no evidence of efficacy of such treatment.

When influenza is treated, resistance to amantadine and rimantadine often develops, and the development of resistance to either of them causes inefficiency of both. Resistance that develops during treatment does not affect the effectiveness of treatment in other patients, but can lead to the transmission of resistant viruses. Resistance to acetylamivir and zanamivir is not clinically significant. The administration of acetylamivir in children can reduce the incidence of otitis media, but there is no other evidence indicating that influenza treatment prevents the development of complications.

Influenza A is treated with amantadine and remantadine; it inhibits the penetration of the virus into the cell. Influenza treatment is discontinued after 3-5 days or 1-2 days after the symptoms stop. For both drugs, 100 mg 2 times a day. To avoid side effects, as a result of accumulation of the drug, for children the dose is reduced (2.5 mg / kg 2 times a day, but not more than 150 mg per day for children under 10 years or 200 mg per day for children over 10 years old). In patients with impaired renal function, the dose is reckoned in accordance with the creatinine clearance. If there is a violation of liver function, the dose of remantadine should not exceed 100 mg per day. Dose-dependent effects from the central nervous system occur in 10% of individuals receiving amantadine (causing increased excitability, insomnia), and 2% receiving remantadine. These effects can be observed within 48 hours after the start of treatment, the most pronounced in the elderly and people with CNS pathology or impaired renal function, and often go through with the continuation of admission. Anorexia, nausea and constipation may also occur.

Influenza A and B are also treated with neuraminidase inhibitors oseltamivir and zanamivir. Dosage of zanavir 10 mg (2 inhalations) 2 times a day, oseltamivir - 75 mg 2 times a day for patients over 12 years. The dose is reduced in younger patients. These drugs have relatively minor side effects. Zanamivir should not be given to patients with hyperreactivity of the bronchi, as it causes bronchospasm with inhalation. Oseltamivir can cause nausea and vomiting.

Influenza: antiviral treatment

Influenza can be prevented by vaccination, but some antiviral drugs are also effective. Antiviral treatment of influenza is indicated for individuals who had been vaccinated less than 2 weeks ago; patients to whom vaccination is contraindicated, as well as immunocompromised patients in whom the immune response to the vaccine may not be sufficient. Taking medication does not affect the development of specific immunity. Admission of antiviral drugs may be discontinued 2 weeks after vaccination; In the absence of vaccination, they should be taken throughout the epidemic.

As measures of prevention against the influenza A virus, amantadine and remantadine are used. Neuraminidase inhibitors oseltamivir and zanamivir are effective against influenza A and B. The dosage of these drugs is the same as for treatment, with the exception of oseltamivir, 75 mg once a day.

Vaccines against influenza

Influenza vaccines are modified annually to include the most frequent serotypes (usually serotype 2 of influenza A and 1 of influenza B). If the vaccine against influenza contains the serotype of the virus that circulates in the population, the incidence in adults can be reduced by 70-90%. In the elderly who are in nursing homes, the effectiveness of vaccination is somewhat lower, but it allows to reduce the lethality from pneumonia by 60-80%. If the antigenic composition of the virus changes significantly (antigenic drift), the vaccine provides only weak immunity.

Vaccination is especially important for the elderly; for those suffering from cardiac, pulmonary and other chronic diseases; for persons caring for patients at home or in medical institutions; for pregnant women, who have the 2nd and 3rd trimester of pregnancy for the winter period. Vaccination by intramuscular injection is best done in the autumn, so that by the time of the greatest incidence of influenza (in the US from November to March) antibody titers were high. Vaccination of all children aged 6-24 months and persons in contact with them is recommended. Regardless of the change in the vaccine strain, immunization should be done annually to maintain high antibody titers.

Inactivated influenza vaccine is given intramuscularly. Adults inject 0.5 ml. Among children there are few who have already had flu, and if there was no previous immunization, both primary and repeated vaccination (at the age of 6 months to 3 years, 0.25 ml, from 3 to 10 years - 0.5 ml) at intervals of 1 month. Adverse reactions are rare and insignificant - there may be pain at the injection site, occasionally - fever, myalgia. Vaccination is contraindicated in individuals who have a history of anaphylactic reactions to chicken meat or egg whites.

In the US, a live attenuated influenza vaccine has been made available for vaccination of healthy individuals aged 5-50 years. The vaccine against influenza is contraindicated in patients of high risk, pregnant women, medical personnel working with immunodeficient patients, children receiving aspirin therapy. The flu vaccine is given intranasally, 0.25 ml per nostril. Children aged 5-8 years who were not vaccinated before attenuated vaccine should receive a second dose of the vaccine, maximum 6 weeks after the first dose. Side effects are easy, often a small rhinorrhea.

How to prevent the flu?

The flu can be prevented through the implementation of an annual vaccination. In certain situations, antiviral chemoprophylaxis is useful. Prevention is indicated to all patients, but is especially important for people from high-risk groups and medical personnel.