Hong Kong flu is an acute respiratory disease caused by the H3N2 serotype of the influenza A virus. The clinical features of the disease are damage to the respiratory and digestive systems, as well as poorly controlled high fever. Symptoms of this type of flu are dry cough, sore throat, headache, nasal congestion, pronounced weakness, dyspepsia. Diagnostics includes methods for detecting the pathogen in the body’s biological fluids, as well as antibodies to it. Treatment consists of etiotropic antiviral therapy and symptomatic methods (detoxification, antipyretic drugs, mucolytics and others).
Hong Kong flu is an infection of the respiratory tract caused by the avian influenza virus mutated in the middle of the twentieth century. The pathology was first known in 1968-1969, when the first outbreak of this disease occurred in Hong Kong, Vietnam, Singapore, the USA, Australia and some African countries with more than half a million deaths. The repeated mutation of the virus led to the emergence of new outbreaks around the globe in 2016-2017. The seasonality of the disease is determined by the cold season (autumn and winter); the greatest number of deaths and complications occur in early childhood (up to 5 years) and the elderly (over 65).
The causative agent of the disease is influenza virus type A (H3N2), belonging to the family of Orthomyxoviruses. The pathogen is unstable in the environment, dies during boiling, when exposed to standard doses of disinfection solutions, ultraviolet irradiation. The source of infection is a sick person, the transmission routes are airborne (when sneezing, coughing, runny nose) and contact (when using common hygiene items and cutlery without treatment, non–compliance with “cough etiquette”).
The risk groups for morbidity are children, elderly people, pregnant women, HIV-infected people, patients with chronic somatic pathologies, malignant neoplasms receiving immunosuppressive therapy; medical workers, military personnel, students, schoolchildren, teachers, service sector employees. The prevalence of this nosology is ubiquitous, but Southeast Asia is traditionally considered a high-risk region.
The penetration of the influenza virus into the epithelial cells of the nasopharynx, trachea, bronchi is manifested by massive destruction of epithelial cells, a decrease in the barrier function of the mucous membrane. The consequence of this is the ingress of the pathogen, the products of its vital activity and cell necrosis into the blood. The proteins neuraminidase and hemagglutinin contained on the surface of the virus cause neurotoxic action and violation of the rheological properties of blood. All together, it has a pronounced intoxicating effect, in severe cases leading to infectious and toxic shock. A feature of the pathogenesis of Hong Kong flu is considered to be a rapid immune response of the body to the presence of this virus and its more favorable course. Most likely, this effect is associated with the antigenic structure of the pathogen and the characteristics of immunity. It has been proven that antibodies to neuraminidase persist in the human body for up to 20 years or more, protective proteins to hemagglutinin also persist for a long time.
The incubation period of infection is 1-2 days. The disease is characterized by a rapid onset, prolonged course (10-14 days) and pronounced symptoms of intoxication. The onset of the disease is acute, with a sharp rise in body temperature (up to 39.5 ° C and above), while often the patient can even name the exact time of the onset of the deterioration of well-being. Soon, headache, redness of the eyes, soreness when moving the eyeballs, terrific chills, muscle and joint pain, digestive disorders (nausea, less often vomiting, liquid watery stools up to 10 or more times a day), decreased appetite and pronounced weakness are added. After a day or two, sore throat, nasal congestion, dry cough are added.
Dangerous symptoms for the prognosis of the course of pathology are considered to be a violation of productive contact with the patient, episodes of convulsions and loss of consciousness, the occurrence of gushing vomiting at the height of headache, progressive muscle weakness in the extremities, the appearance of nasal, gingival, organ bleeding and small-point (petechial) rash on the body, increasing respiratory failure (shortness of breath, acrocyanosis), decreased the amount of urine.
Timely seeking medical help and taking effective medications almost always neutralize possible complications. The most frequent consequences of influenza are bacterial inflammatory processes in various organs and systems. First of all, it is pneumonia, inflammation of the paranasal sinuses (sinusitis, frontitis), otitis, as well as pyelonephritis, myocarditis, less often meningoencephalitis, infectious and toxic shock. In addition, many diagnostic and therapeutic manipulations can lead to a violation of the integrity of the skin and mucous membranes and cause the appearance of local purulent processes (abscesses, phlegmons), as well as a generalized septic process in immunodeficient individuals.
To diagnose Hong Kong flu, it is mandatory to consult an infectious disease specialist, a pulmonologist (after the appearance of symptoms of lung damage), a gastroenterologist (in the presence of gastroenteritis). If this type of flu is suspected , the following diagnostic methods are used:
- Objective inspection. Physical examination reveals the presence of respiratory insufficiency (forced posture, shortness of breath, acrocyanosis phenomena), deafness of heart tones, the degree of impaired consciousness, symptoms of damage to the meninges and brain matter. When examining the oropharynx, hyperemia of the pharynx, nasal mucosa is determined, single or diffuse dry wheezes can be heard in the lungs.
- Laboratory blood tests. In a general clinical blood test, leukopenia, lymphocytosis, and moderate acceleration of ESR are recorded. At the peak of fever, minor proteinuria and microhematuria may appear in the general urine analysis (with a decrease in body temperature, these indicators normalize). Biochemical blood testing is usually within the physiological norm, there may be an increase in CRP.
- Identification of infectious pathogens. PCR diagnostics is carried out by examining nasal discharge, sputum, smears from the nasopharynx, throat. Antibodies to the virus are registered with the help of ELISA, while venous blood is taken twice with an interval of 2-3 weeks to detect the growth of the antibody titer (twice or more). There are express tests (sensitivity 99%, specificity 98-99%) for the diagnosis of influenza at home and on an outpatient basis, based on the immunochromatographic method. The nasopharyngeal contents usually serve as the material for the study.
- Radiation diagnostics. Chest x-ray and paranasal sinuses, ultrasound of the abdominal cavity and kidneys is necessary for the early detection of infectious complications and differential diagnosis of Hong Kong flu.
Differential diagnosis is carried out with other acute respiratory infections, sepsis, meningococcal infection, typhoid fever, tuberculosis, malaria, paratyphs A and B, generalized salmonellosis, typhus. A similar clinical picture is observed in pneumonia, bronchitis, tonsillitis, debuts of diffuse connective tissue diseases, pyelonephritis, purulent processes in the abdominal cavity (hepatic abscesses), retroperitoneal space (kidney carbuncle), chest (clouded pleurisy), pelvis (adnexitis).
In the presence of clinical and epidemic indications, patients with suspected infection are subject to hospitalization, sometimes treatment at home is possible. No special diet has been developed, frequent fractional nutrition and dairy-vegetable food are recommended. Much attention is paid to quitting smoking (in order to improve gas exchange in the lungs) and the use of a large amount of liquid (mainly rehydrate or boiled water), since dehydration may occur with prolonged increase in body temperature, increased sweating and dyspepsia. Bed rest is recommended until a steady decrease in body temperature for 2-3 days.
The specific treatment of Hong Kong flu is antiviral drugs, which should be prescribed as early as possible (the first day of the disease and earlier). The most effective drugs are considered to be oseltamivir, zanamivir, imidazolylethanamide of pentanedioic acid; currently, the drug baloxavir is in clinical trials.
The means of symptomatic therapy are detoxification drugs (glucose, saline solution, chlosol, trisol, reamberin), antipyretics (diclofenac, celecoxib), local antiseptics (solutions of furacilin, chlorhexidine, calendula), mucolytics (acetylcysteine), vasoconstrictive nasal drops and others. With the phenomena of liquid stools, nausea, vomiting, sorbents (colloidal silicon dioxide, activated carbon), enzymes (pancreatin, lipase) are prescribed.
Prognosis and prevention
The prognosis for Hong Kong flu is favorable, the mortality rate is no more than 0.5%, which is associated with possible immunity among people who suffered the disease in the middle of the last century, restriction of mass events (quarantine), provision of proper medical care and the use of antiviral and antibacterial agents (for timely treatment of bacterial complications).
The only method of effective specific prevention of influenza is vaccination. Vaccines contain surface antigens of the most relevant influenza viruses in this epidemic season (at least 15 micrograms of hemagglutinin according to WHO recommendations). The addition of immunomodulators (polyoxidonium, sovidone) to influenza vaccines has no proven effectiveness. Nonspecific prevention of influenza consists in avoiding crowded places, using masks and respirators indoors, maintaining an adequate microclimate, wet cleaning, washing hands and face with soap after coming home.