Influenza - Diagnosis

Diagnosis of flu during an epidemic outbreak is not difficult. It is based on identifying typical manifestations of the disease (intoxication, catarrhal syndrome mainly in the form of tracheitis).

Rapid diagnostics of influenza is based on the immunofluorescence method (virus antigens are detected in smears and nasal prints). To establish a final diagnosis, it is necessary to isolate the pathogen from the clinical material obtained from the patient by infecting cell cultures or chicken embryos and identify the isolated virus. Retrospectively, the diagnosis is established by an increase in the antibody titer in paired blood serums of patients.

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Indications for hospitalization

Patients with severe or complicated cases of influenza, as well as with a number of concomitant diseases, are subject to hospitalization: severe forms of diabetes mellitus, chronic coronary heart disease, chronic non-specific lung diseases, blood diseases, and diseases of the central nervous system.

Syndromic indications for hospitalization include:

• high fever (above 40 °C);
• disturbances of consciousness;
• repeated vomiting;
• meningeal syndrome:
• hemorrhagic syndrome;
• convulsive syndrome;
• respiratory failure;
• cardiovascular failure.

Hospitalization and isolation of patients are also carried out according to epidemiological indications. (Dormitories, boarding schools, orphanages, hotels, transport, military units, penitentiary institutions.)

Differential diagnosis of influenza

Differential diagnosis of influenza is carried out with two groups of infectious diseases:

• diseases accompanied by catarrhal-respiratory syndrome;
• diseases characterized by the early development of febrile-intoxication syndrome.

The first group includes other acute respiratory viral infections, in which (unlike flu) cough, runny nose, pain and sore throat precede the rise in temperature and are not accompanied by general symptoms of intoxication (absent or appear on the 2-3rd day of the disease; expressed moderately, but can last longer than with flu). The combination of fever, intoxication and lymphadenopathy with catarrhal phenomena allows to exclude flu and assume the presence of measles, yersiniosis or infectious mononucleosis. Since the digestive organs are not involved in the pathological process with flu, this allows to exclude this disease with a combination of fever and catarrhal phenomena with dyspeptic syndrome. In this case, the presence of viral diarrhea (rotavirus, Norwalk virus ), as well as yersiniosis or measles in adults is possible.

In many acute forms of infectious diseases, a flu-like clinical picture is expressed in the first 1-2 days of the disease. In this case, the distinctive features of influenza should be taken into account: severe chills are rarely detected; the peak of intoxication is on the 1-2nd day of the disease; lymphadenopathies, enlargement of the spleen and liver never occur; tracheitis is expressed from the 2-3rd day; the duration of fever (in the uncomplicated form) is 3-4 days (no more than 5-6 days): relative bradycardia or the correspondence of the heart rate to the body temperature level is characteristic.

In practice, flu is misdiagnosed in staphylococcal diseases (scarlet fever, tonsillitis, erysipelas), community-acquired pneumonia (before the appearance of characteristic symptoms), meningococcal infection, malaria, pyelitis, rickettsiosis, typhoid fever and salmonellosis (before the appearance of dyspeptic syndrome), leptospirosis (in the warm season), viral hepatitis A, hemorrhagic fevers, trichinosis.

In difficult to diagnose cases, the doctor must assess the severity of the patient's condition, the need and timing of a repeat examination or emergency hospitalization. In this case, antibiotics and antipyretic drugs should be avoided, as they can significantly complicate further diagnostics and create the illusion of improvement in the patient's condition.

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