Causes

Causes

Influenza spreads rapidly and can cause seasonal epidemics every year. Outbreaks can occur in places where people gather, such as schools, childcare institutions, and nursing homes.

A global study showed an infection rate of 10.7% and a prevalence rate of 4.4% in adults and 7.2% in people over 65 years of age.

The annual periodicity of influenza in my country changes with the increase of latitude, and shows a variety of spatial patterns and seasonal characteristics:

1.    The northern provinces north of 33 degrees north latitude show a winter epidemic pattern, with a single annual peak in January and February every year;

2.    The southernmost provinces south of 27 degrees north latitude have a single annual peak from April to June every year;

3.    In the mid-latitude regions between the two, there are double-cycle peaks in January-February and June-August every year.

According to the World Health Organization (WHO), seasonal influenza can cause 3 to 5 million severe cases and 290,000 to 650,000 deaths worldwide each year.

All children under 5 years of age are considered at high risk for severe influenza, but children under 2 years of age are at highest risk, and infants under 6 months of age have the highest rates of hospitalization and death.

High-risk groups such as pregnant women, infants, the elderly, and patients with chronic underlying diseases have a higher risk of severe illness and death after contracting influenza.

Influenza vaccination is the most effective means of preventing influenza virus infection and its serious complications.

Source of infection

Influenza patients and asymptomatic infections are the main sources of infection.

The patient is contagious 1 to 7 days after the onset of the disease, and the most contagious is the 2 to 3 days at the beginning of the disease.

Way for spreading

Influenza is mainly transmitted by droplets such as sneezing and coughing. Influenza virus survives in the air for about half an hour, and can be infected through direct or indirect contact with mucous membranes such as the mouth, nose, eyes, etc., and can also be infected by contact with items contaminated by the virus.