Influenza

Symptoms usually appear suddenly, with a high fever above 38°C, accompanied by chills, headache, muscle and joint pain, and a dry, persistent cough. Intense fatigue, loss of appetite and a general feeling of malaise are common. These signs indicate a marked systemic infection, much more severe than a simple cold. The rapid onset of symptoms is one of the distinguishing features of influenza compared to other more common viral respiratory infections.
In children, clinical manifestations may include nausea, vomiting or abdominal pain accompanied by diarrhoea, in addition to the usual respiratory signs.
In elderly or immunocompromised individuals, fever may be absent, giving way to a deterioration in general health, confusion or extreme fatigue.
The incubation period varies between one and four days. The illness lasts on average one week to ten days, but coughing and fatigue can persist for several weeks, especially in vulnerable individuals.
The so-called ‘classic’ forms of influenza systematically combine respiratory symptoms (cough, sore throat, nasal congestion) and general signs (fever, muscle aches, headaches), although the intensity and combination of symptoms may vary depending on age, health status or the viral strain in circulation

Influenza is caused by a viral infection linked to the influenza A or B viruses. The virus is mainly transmitted through the air, via respiratory droplets expelled when coughing, sneezing or even talking. Contact with contaminated surfaces, followed by contact with the nose, eyes or mouth, can also cause infection.
Each year, one to two subtypes of the Influenza A virus and type B lineages (Victoria, Yamagata) cause seasonal epidemics. The ability of these viruses to mutate, a phenomenon called antigenic drift, complicates the acquisition of lasting immunity in the population. This also explains the need for an annually updated vaccine.

The virus infects respiratory epithelial cells via two surface proteins: haemagglutinin (HA) and neuraminidase (NA). These proteins determine viral subtypes and are responsible for the regular emergence of new strains, against which the population is only partially immune. The contagious period begins about one day before the onset of symptoms and lasts up to 7 days after their onset. This period may be longer in children or immunocompromised individuals.

Influenza can affect anyone, regardless of age or health status. However, certain situations expose individuals to a higher risk of developing a severe form of the disease or associated complications. Medical data show that age is an important determining factor.
Infants, young children and people aged 65 and over are more vulnerable to influenza infection. In these populations, the immune system often responds less effectively to viral attack, leading to a longer or more severe illness.
The presence of chronic diseases is also a recognised risk factor. People with respiratory, cardiovascular, metabolic or neurological conditions, as well as those with kidney or liver failure, are more susceptible to complications from influenza. Immunodeficiency, whether related to an underlying disease or medication, also increases the likelihood of severe forms of the disease. Pregnancy, particularly in the second and third trimesters, is associated with a higher risk of complications due to the physiological and immune changes it induces.
Other factors, such as severe obesity or living in a community setting, particularly in medical-social establishments, promote transmission and complicated forms of the disease. All of these factors explain why specific recommendations for prevention and management are made for certain population groups.

The diagnosis of influenza is based primarily on clinical assessment, particularly during seasonal epidemics. The sudden onset of suggestive symptoms (fever, dry cough, myalgia, headache, intense fatigue) in an unvaccinated patient or a patient belonging to a risk group strongly suggests influenza infection. However, biological confirmation remains important in certain contexts: hospitalisation, severe forms, immunodepression, or in the context of epidemiological surveillance.
The following tests are available:

• Rapid antigen detection tests (RIDTs): accessible and quick, but not very sensitive. A negative result therefore does not rule out influenza.
• Molecular tests (RT-PCR): the gold standard. Highly sensitive and specific, they can identify the type and subtype of the virus.
• Viral culture: rarely used in clinical practice as it takes several days, but remains valuable for virological surveillance and assessing sensitivity to antivirals.

In hospitalised patients, if influenza is highly suspected despite a negative antigen test, it is recommended to continue investigations using RT-PCR on a nasopharyngeal or sputum sample, or even on a sample from the lower respiratory tract in cases of severe lung involvement

Although influenza is generally self-limiting, it may require medication in some cases, particularly in people at risk or with severe forms of the disease. Treatment focuses on two main areas: symptomatic relief and the use of antivirals.

Symptom relief

Fever, headaches and muscle aches can be alleviated by administering paracetamol or non-steroidal anti-inflammatory drugs (NSAIDs), unless contraindicated. In children, the use of aspirin should be avoided due to the risk of Reye's syndrome.
Good hydration is essential. Rest is recommended, and it is advisable to avoid exposure to public places for as long as the fever persists.

Antiviral treatment

Antiviral drugs are recommended in several situations: hospitalisation, severe progressive disease, or the presence of risk factors. They are most effective when administered within the first 48 hours after the onset of symptoms.

In patients with severe disease or influenza pneumonia, prolonged treatment (up to 10 days) may be considered, particularly in cases of immunosuppression or persistence of the virus in respiratory samples.

In most healthy individuals, influenza resolves within about ten days, although some symptoms, such as cough and fatigue, may persist longer. However, in some situations, the infection can develop into severe, even life-threatening forms.
Pneumonia is the most common complication. It can be primary, of viral origin, or secondary, linked to a bacterial superinfection. The latter often manifests itself as an initial improvement followed by a relapse with fever, purulent sputum and deterioration of the general condition.
Other serious complications include:

• Encephalitis and convulsions, particularly in children.
• Myositis or rhabdomyolysis, causing severe muscle pain and elevated muscle enzymes.
• Cardiac complications, such as myocarditis, pericarditis, or myocardial infarction.

In elderly people or those with chronic conditions, influenza can also exacerbate pre-existing conditions such as heart failure, diabetes or COPD, significantly increasing the risk of hospitalisation and mortality

Influenza prevention is based on a set of measures aimed at reducing the risk of infection and limiting the spread of the virus within the population. Vaccination is the most effective and widely recommended prevention strategy. Influenza vaccines are adapted each year to match the viral strains most likely to circulate during the winter season. This regular adjustment is necessary due to the genetic variability of influenza viruses. In Switzerland, vaccination is available at pharmacies in most cantons. Vaccination is particularly recommended for people at increased risk of complications, such as the elderly, pregnant women, infants, people with chronic diseases and immunocompromised individuals. It is also recommended for the people around them and for healthcare professionals, in order to limit transmission in healthcare settings. Although vaccination does not guarantee absolute protection against infection, it significantly reduces the risk of severe forms of the disease, hospitalisation and serious complications.
In addition to vaccination, simple hygiene measures play an important role in prevention. Regular hand washing, ventilating enclosed spaces, cleaning frequently touched surfaces and adopting behaviours that limit the spread of respiratory droplets help to reduce the circulation of the virus. These measures are particularly relevant during seasonal epidemics, when influenza is highly transmissible

Although influenza is usually mild, certain situations should raise alarm bells and prompt an immediate visit to the doctor.
It is recommended that you seek medical advice in the event of:

• High fever persisting for more than three days or reappearing after initial improvement, suggesting a possible secondary infection.
• Difficulty breathing, shortness of breath at rest, chest pain or cyanosis.
• Altered state of consciousness, confusion, unusual drowsiness.
• Signs of dehydration, such as dry mouth, decreased urine output or dizziness.
• Severe muscle pain, extreme weakness, convulsions.

In children, particular attention should be paid to rapid breathing, unusual irritability, difficulty drinking or eating, or a pale or greyish complexion.
In elderly people, flu can present in a more atypical way, with no fever but disorientation or a sudden decline in independence.
Finally, any worsening of a chronic condition (asthma, diabetes, heart disease) must be taken seriously and treated appropriately by a doctor

At Hôpital de La Tour, the care of patients with influenza is based on a multidisciplinary and personalised approach. Upon arrival, patients with respiratory symptoms are referred according to a rigorous triage protocol, ensuring the safety of all.
In the event of complications, patients may be admitted to units providing continuous care, intensive care or internal medicine, ensuring a high level of medical follow-up.
Hôpital de La Tour also emphasises prevention: every autumn, a vaccination campaign is offered to its employees with the aim of protecting the community.

Is influenza a dangerous disease?

Influenza is generally mild, but it can lead to serious complications, particularly respiratory or cardiac complications, in vulnerable individuals.

What is the difference between influenza and a common cold?

A cold starts gradually and mainly causes nasal symptoms. Influenza, on the other hand, starts suddenly with a high fever, muscle aches and intense fatigue.

Do you need to get vaccinated every year?

Yes. The influenza virus is constantly changing. The vaccine is therefore updated every year to be effective against the circulating strains.

Can you catch influenza if you have been vaccinated?

Yes, but the symptoms are generally milder. The vaccine mainly reduces the risk of complications and hospitalisation.

What are the warning signs that require urgent medical attention?

Difficulty breathing, chest pain, persistent fever, confusion, severe weakness, or worsening of a chronic illness are signs that warrant immediate medical attention.

Are antibiotics useful against influenza?

No, because influenza is a viral infection. Antibiotics are only indicated in cases of proven bacterial superinfection.

How long are you contagious when you have influenza?

Contagiousness begins about one day before symptoms appear and generally lasts 5 to 7 days. In children or immunocompromised individuals, this period may be prolonged.

Can antiviral medication be taken without a prescription?

No. Antiviral medication must be prescribed by a doctor and is reserved for certain specific cases, particularly high-risk individuals or severe forms of the disease.