Influenza and Radiology: be aware that pneumonia can develop following poorly treated influenza.
Winter is coming. The media are talking about the flu. You have a persistent cough, a fever that won't go down. You think: "It's just the flu, it'll pass."
However, for some people, the flu doesn't "go away". It becomes complicated.
Each year in Switzerland, influenza causes several thousand hospitalizations (approximately 3,500 during the winter of 2022-2023) and several hundred deaths. The 2024/2025 influenza epidemic was particularly severe, beginning in early December and lasting for three months.
The problem? Pneumonia often strikes without warning. And without rapid medical imaging, it can become serious very quickly.
That's why we, radiologists, would like to explain to you: how to recognize when the flu is getting worse, and above all, why chest radiology is your best ally to avoid the worst.
Flu: The illness that is thought to be benign, but which can become serious
What exactly is it?
- High fever (around 39°C)
- Intense fatigue (asthenia)
- Dry cough (no mucus, just an irritating cough)
- Muscle and joint pain (aches and pains)
- Chills M
- to the head
In most healthy people, the flu clears up within a week. But fatigue can last 3-4 weeks afterwards.
The problem: In some people, the virus creates a "breach" — it weakens the immune system so much that bacteria enter the lungs and create a secondary infection: pneumonia.
Who is at risk of complications?
Vulnerable individuals are at increased risk of severe flu:
- Elderly people (over 65 years old)
- Pregnant women
- Infants (< 6 months)
- People with chronic illnesses: diabetes, asthma, COPD, heart or kidney failure, respiratory failure
- Immunocompromised individuals (HIV, cancer, after chemotherapy)
- Obese people
The silent complication: Post-flu pneumonia
How pneumonia occurs
Here's what's happening on the medical front:
When you have the flu, your immune system fights the virus. This fight temporarily weakens your defenses against bacteria. The three most common bacteria that take advantage of this are:
- Streptococcus pneumoniae (pneumococcus)
- Staphylococcus aureus
- Haemophilus influenzae
They travel up to the lungs and cause inflammation. The alveoli fill with fluid or pus, preventing oxygen from passing properly into the blood.
The figures that should alarm you
Here's what medical studies say:
- 75% of flu patients who develop pneumonia have a secondary bacterial infection, not just a viral one. These bacterial pneumonias are one of the most frequent causes of sepsis (a generalized blood infection).
- In 2008, a study in the United Kingdom found that pneumonia accounted for 46% of all sepsis cases.
- The case fatality rate of untreated bacterial pneumonia ranges from 5% to 30%, depending on the severity.
In short: The flu that turns into pneumonia can very quickly become a matter of life or death.
Symptoms that should alert you
You have the flu, and you notice:
- A cough that worsens (instead of improving after 5-7 days)
- A fever that rises again after having decreased (fever again > 39°C)
- Shortness of breath or difficulty breathing during daily activities
- Chest congestion or pain when breathing (side stitches)
- Expectoration of sputum with color (yellow, green, or tinged with blood)
- Fatigue that worsens instead of improving
- Mental confusion or abnormal behavior
- A very high fever (> 40°C)
If you have ONE of these symptoms, consult your doctor. If you have MORE than ONE, go to the emergency room. Don't delay.
How radiology detects pneumonia before it's too late
Why a clinical examination is not enough
Your doctor can listen to your lungs, ask you to cough, and take a blood sample. But the human ear can't see inside the lungs. Blood tests can show an infection, but not exactly where it is.
This is where medical imaging comes in.
Chest X-ray:
the first (and often the only) examination needed
A chest X-ray allows visualization of the lungs and detection of pneumonia. It shows:
- An opacity (a white or grey area) in the lungs — that's an infection
- A localized focus of infection (pneumococcal pneumonia, usually unilateral — affecting only one lung)
- A diffuse infiltrate (if it is viral or Mycoplasma pneumonia, several areas may be affected)
- An effusion (fluid accumulates around the lungs — this is a sign of severity)
Advantages of radiography:
- Quick (5-10 minutes)
- Very little exposure to X-rays (much less than a CT scan)
- Inexpensive
- Widely available
- Sufficient for 90% of uncomplicated pneumonias
Limitations:
- Less detail than an MRI or a CT scan
- May not show some small foci in very early stages
Chest CT scan: when more detail is needed
If the X-ray shows nothing but the symptoms worsen, or if your doctor suspects a complication (lung abscess, large effusion), a chest CT scan may be requested.
At CID Lausanne, we have an Ultra Low Dose CT scanner specifically designed for the lungs. It offers:
- Superior precision
- An 80% reduction in radiation exposure compared to conventional scanners
- An ability to detect even small pulmonary nodules
- Regular monitoring is possible without radiative guilt.
This is particularly important if you have had previous pneumonia or are a frail person: you can be monitored regularly without accumulating dangerous doses.
Early detection vs. late emergency: the importance of timing
The Classic Mistake: "It'll pass, I'll just wait"
Many people wait. They tell themselves: "It's just the flu, my body will fight it off." And for healthy people without risk factors, that's often true.
But not always.
And when it gets worse, it gets worse FAST.
Between 48 and 72 hours, untreated pneumonia can go from "manageable at home with antibiotics" to "hospitalization in intensive care with mechanical ventilation".
The real clinical case
Imagine Margot, 68 years old, a chronic diabetic. She has the flu. She stays home, takes paracetamol, and drinks a lot. On day 5, her cough worsens, she's tired, but she tells herself it's normal.
On day 7, she felt suffocated while climbing the stairs. She went to the emergency room.
A chest x-ray reveals: bilateral pneumonia (both lungs are affected), with the beginning of sepsis.
She was hospitalized. She received IV antibiotics. She spent 8 days in the hospital. She was lucky: she pulled through.
But what if she had consulted a doctor on day 5? An X-ray would have shown the early signs of pneumonia. Oral antibiotics would have stopped it at home. No hospitalization. No complications.
Time = lives saved.
Prevention: vaccination is your best ally
Flu vaccination in Switzerland
In Switzerland, the best prevention remains annual flu vaccination.
The Federal Office of Public Health (FOPH) expressly recommends getting vaccinated between mid-October and the start of the flu season for the following groups:
- Pregnant women (from the second half of pregnancy onwards)
- People aged 65 or over
- People with chronic illnesses (diabetes, asthma, COPD, heart or kidney failure)
- Immunocompromised individuals
- Infants and children (from 6 months for some vaccines)
- Healthcare workers and people in regular contact with patients
- People in contact with poultry or wild birds
Why get vaccinated? Because:
- It reduces the risk of contracting the flu
- Even if you contract it despite being vaccinated, the symptoms are milder and the duration shorter.
- It drastically reduces the risk of complications — especially pneumonia
- It also protects the people around you (infants, the elderly)
- It is covered by basic health insurance (LAMal) for the recommended groups.
Flu vaccination is covered by your mandatory health insurance (LAMal) if you belong to one of the recommended groups. Consult your doctor or a pharmacy to get vaccinated—most Swiss pharmacies are authorized to administer it.
Good to know: Unlike an X-ray, vaccination does not towards your deductible. It is a preventative measure covered directly.
If you have contracted the flu: antiviral medication
If you have had symptoms for less than 48 hours, your doctor may prescribe an antiviral such as oseltamivir (Tamiflu®).
These medications:
- They reduce the duration of the illness
- They reduce the severity of symptoms
- They reduce the risk of complications and mortality
But it's a race against time: they only work if you take them quickly.
Checklist: When to consult and what to do
If you have flu symptoms
Consult your doctor IMMEDIATELY or go to the emergency room if:
- You are over 65 years old
- You are pregnant
- You have a chronic illness (diabetes, asthma, heart failure, etc.)
- You have a very high fever (> 40°C) that does not go down with paracetamol.
- You have difficulty breathing or chest congestion
- You are experiencing confusion or abnormal drowsiness
- You've had a cough for more than 7 days and it's getting worse
- You have general symptoms that worsen instead of improving after 5-7 days
Otherwise, if you are in good health:
- Rest, hydration, paracetamol
- Regular hand washing
- Wear a mask if you are around vulnerable people.
- Call your doctor on day 3-5 if there is no improvement
Your doctor may ask:
- A chest X-ray (to rule out pneumonia)
- A blood test (to confirm that there is no bacterial infection)
- A flu test (if it's not clinically clear)
Radiology at CID Lausanne: speed, precision, safety
Why Us?
At CID Lausanne, we understand the urgency of complicated influenza. We have:
State-of-the-art equipment:
- Ultra-fast digital radiography (results in minutes, not days)
- CT Ultra Low Dose for cases that require more detail
- AI technology to analyze images faster and more accurately
Accessibility:
- Free transport service for patients who are unable to travel (particularly important in winter when one is vulnerable)
- Rapid turnaround times — suspected cases of pneumonia are given priority
- Expert radiologists who know how to recognize severe forms and complications
Humanity:
- We understand that you are ill, anxious, potentially in an emergency situation
- Our team is trained to receive patients in respiratory distress.
- Rapid reports sent directly to your doctor
What happens if you come in for a chest X-ray?
Duration: 10-15 minutes from start to finish
Procedure :
- Welcome and registration (2 min)
- Preparation: You are asked to take your shirt off; no metal objects.
- X-ray: you remain standing, you are asked to breathe normally, then to hold your breath for a few seconds (very quickly).
- Analysis: The radiologist looks at the images
- Results: Written report sent to your doctor within 2-4 hours
Radiation exposure: Very low — less than a day's natural radiation. Pregnant women can have it (if it's not an emergency, it's best to wait until the second trimester, but in an emergency, diagnosis takes precedence).
Frequently Asked Questions
"I'm just tired but I don't have a fever. Is it really the flu?"
"What if I can't afford an X-ray?"
In Switzerland, diagnostic X-rays are covered by mandatory health insurance (LAMal). You will have to pay your deductible (CHF 300-2,500 depending on your choice), then a 10% co-payment (capped at CHF 700/year).
Don't delay for financial reasons. An X-ray costs far less than emergency hospitalization in intensive care.
"Why does the flu turn into pneumonia in some people and not in others?"
Good question. Several factors are involved:
- Age (older = more fragile)
- Pre-existing chronic diseases
- The personal immune system
- The virus strain (in some years the virus is more aggressive) V
- our respiratory hygiene and diet
- Smoking (smokers = doubled risk)
You can't control everything, but vaccination and early detection, yes.
"After a normal X-ray, the pneumonia disappeared?"
Not exactly. A normal chest X-ray means there's no detectable pneumonia (yet). But if your symptoms worsen after a normal X-ray, a second X-ray a few days later could reveal developing pneumonia.
That is why clinical monitoring is just as important as X-rays.
Listen to your body, consult a doctor in time.
The flu may seem trivial. But for some people, it's a real medical issue.
You're not being paranoid by seeking medical help for a worsening flu. You're being cautious.
And a chest X-ray is not a useless examination: it's insurance.
It costs little, exposes you to very little radiation, and can save your life by detecting pneumonia in time.
Resources & Links
- FOPH (Federal Office of Public Health): Influenza and respiratory virus situation
- Infovac: Flu vaccination in Switzerland ( www.infovac.ch )
- Federal Office of Public Health (FOPH): Seasonal flu and recommendations
- Breath Foundation: Pneumonia and Diagnosis
- Vacciner-suisse.ch: Personalized vaccination recommendations
Summary: Key points to remember
Do
The common flu disappears in 1 week
75% of post-flu pneumonias are bacterial.
Vaccination reduces complications by 70%
An X-ray detects 90% of pneumonias
X-ray radiation = 1 natural day
Untreated pneumonia can be fatal
Impact
Wait 5-7 days before getting alarmed.
Antibiotics work, but you have to take them quickly.
Get vaccinated every winter if you are at risk
Consult a doctor if it worsens after day 5
No risk, go ahead without fear
Don't delay — lives depend on swift action
