Health Care Professionals Influenza Flu Resources

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Influenza is a public health problem with considerable epidemiological, clinical and economic impact. This is attributable to several factors: the ubiquity and contagiousness of the disease, the antigenic variability of viruses, the epidemic (and periodically pandemic) and seasonal trend, the possibility check it out of serious complications in some categories of subjects (children, the elderly, people with comorbidities and chronic diseases), management costs in case of complications and social costs (lost working days, loss of productivity, etc.).

Influenza is an acute respiratory disease caused by influenza viruses. It is a seasonal disease that, in the western hemisphere, occurs during the winter period. The first isolation in humans dates back to 1933 in England (but previously influenza viruses had already been isolated in both chickens and pigs).

Since then, four different types have been identified

All belonging to the Orthomixoviridae family: types A and B, responsible for classic flu symptoms; type C, of little clinical relevance (generally asymptomatic); type D, whose possibility of infecting humans is not yet clear. Influenza A viruses are further divided into subtypes based on molecular differences in the two surface glycoproteins hemagglutinin (HA) and neuraminidase (NA).

The epidemiology of influenza is based on the marked tendency of influenza viruses to mutate, i.e. present antigenic variations in the two glycoproteins HA and NA which allow them to evade the host’s immune response due to previous infections and therefore find a large part of the immunologically susceptible population and can therefore spread widely and rapidly.

Since then, four different types have been identified

These molecular variations must be taken into account in the preparation of vaccines, the composition of which must be updated every year and in this the surveillance activities are essential to select the specific strains to be included on the basis of the degree of epidemiological and serological difference with respect to what has circulated in previous seasons.

Pandemics occur at unpredictable time intervals and in this century they occurred in 1918 (Spanish, H1N1 subtype responsible for at least 20 million deaths), in 1957 (Asian, H2N2 subtype), in 1968 (Hong Kong, H3N2 subtype). The last flu pandemic, due to the A(H1N1)pdm09 virus occurred in 2009. Consult the dedicated page. However, it is important to underline that the appearance of a strain with radically new surface proteins, therefore of an influenza virus completely different from those previously circulating, is not in itself sufficient for the occurrence of a pandemic. It is also necessary that the new virus is capable of being transmitted from man to man effectively.

The H5N1 subtype viruses isolated from various individuals in Hong Kong

In 1997 did not, fortunately, possess this characteristic. A similar event occurred in 1999, when two children, also from Hong Kong, were found to be suffering from influenza caused by the subtype A(H9N2) virus, usually infectious on birds. Again, however, the virus did not spread to other individuals and no new cases were reported after April 1999.

The unique characteristics of influenza make surveillance activities essential.

And the H5N1 subtype viruses isolated from various individuals in Hong Kong

In particular, it is important to identify the onset, duration and intensity of the seasonal epidemic and the geographical distribution using the estimate of the incidence of influenza-like syndromes (ILI, Influenza Like Illness) and through the early identification of circulating viral strains .

Influenza viruses are mainly transmitted by air and spread very easily through the droplets of saliva that the patient produces by coughing, sneezing or simply talking, especially in crowded and closed environments.

Transmission also occurs by direct contact with infected people (for example through contaminated hands on the eyes, nose or mouth) or through tools or objects, given that the influenza virus can persist for a very long time and penetrate the body through the mucous membranes.

Infected people are contagious from a day or two before symptoms appear until about five days after symptoms start, sometimes up to 10 days afterward. This means that the virus can also be transmitted by apparently healthy people. Children and people with weakened immune systems can be contagious for an even longer time.

The frequency with which cases of flu arise, although very different from internships General informations

Influenza is a public health problem with considerable epidemiological, clinical and economic impact. This is attributable to several factors: the ubiquity and contagiousness of the disease, the antigenic variability of viruses, the epidemic (and periodically pandemic) and seasonal trend, the possibility of serious complications in some categories of subjects (children, the elderly, people with comorbidities and chronic diseases), management costs in case of complications and social costs (lost working days, loss of productivity, etc.).

Mode of transmission

Influenza is an acute respiratory disease caused by influenza viruses.

It is a seasonal disease that, in the western hemisphere, occurs during the winter period. The first isolation in humans dates back to 1933 in England (but previously influenza viruses had already been isolated in both chickens and pigs).

Since then, four different types have been identified, all belonging to the Orthomixoviridae family: types A and B, responsible for classic flu symptoms; type C, of little clinical relevance (generally asymptomatic); type D, whose possibility of infecting humans is not yet clear.

Mode of transmissionInfluenza A viruses are further divided into subtypes based on molecular differences in the two surface glycoproteins hemagglutinin (HA) and neuraminidase (NA).

The epidemiology of influenza is based on the marked tendency of influenza viruses to mutate, i.e. present antigenic variations in the two glycoproteins HA and NA which allow them to evade the host’s immune response due to previous infections and therefore find a large part of the immunologically susceptible population and can therefore spread widely and rapidly.

These molecular variations must be taken into account in the preparation of vaccines, the composition of which must be updated every year and in this the surveillance activities are essential to select the specific strains to be included on the basis of the degree of epidemiological and serological difference with respect to what has circulated in previous seasons.

Pandemics occur at unpredictable time intervals and in this century they occurred in 1918 (Spanish, H1N1 subtype responsible for at least 20 million deaths), in 1957 (Asian, H2N2 subtype), in 1968 (Hong Kong, H3N2 subtype). The last flu pandemic, due to the A(H1N1)pdm09 virus occurred in 2009.

The unique characteristics of influenza make surveillance activities essential

In particular, it is important to identify the onset, duration and intensity of the seasonal epidemic and the geographical distribution using the estimate of the incidence of influenza-like syndromes (ILI, Influenza Like Illness) and through the early identification of circulating viral strains .

Influenza viruses are mainly transmitted by air and spread very easily through the droplets of saliva that the patient produces by coughing, sneezing or simply talking, especially in crowded and closed environments.

Transmission also occurs by direct contact with infected people (for example through contaminated hands on the eyes, nose or mouth) or through tools or objects, given that the influenza virus can persist for a very long time and penetrate the body through the mucous membranes.

Infected people are contagious from a day or two before symptoms appear until about five days after symptoms start, sometimes up to 10 days afterward.

This means that the virus can also be transmitted by apparently healthy people. Children and people with weakened immune systems can be contagious for an even longer time.