‘Just Flu’ Can Turn Serious When Fever Lingers, Breathing Worsens: Pulmonologist

It begins with ‘just flu’. Fever, body ache, sore throat, cough and the familiar feeling of being knocked down by the virus. In most patients, it settles in a few days, leaving behind some tiredness and an irritating cough.

But when the fever refuses to settle, or the patient who seemed to be recovering suddenly finds it difficult to breathe, it is time to take the illness more seriously, warns Pulmonologist Dr Vijay Kumar Agrawal, Director and HOD, Pulmonology and Sleep Medicine and Senior Consultant, Critical Care Medicine, Yatharth Hospital, Faridabad.

He said that he has been seeing patients with influenza A and B, including H1N1 and H3N2, some of whom have gone on to develop significant lung complications.

“What concerns me is that more and more patients are coming with prolonged symptoms and complications after what initially appeared to be a simple flu,” he said.

Dr Agrawal emphasised that influenza remains self-limiting for most otherwise healthy people, but the course of illness matters. “If the fever refuses to settle, the cough is getting worse, or breathlessness develops, the flu should not be taken lightly,” he warned as he gave an instance of a patient he recently treated.

“The patient had apparently recovered from the acute phase of influenza. Instead of returning to normal, however, he developed rapidly progressive changes in both lungs. Imaging showed a pattern that was concerning and appeared similar to interstitial lung disease,” recalled the doctor.

At that stage, the important question was not simply whether the patient had “lung damage”, but what was causing the changes.

Dr Agrawal explained that doctors have to distinguish between ongoing infection, inflammation triggered by the virus and other complications before deciding on treatment.

He also stressed that an imaging pattern resembling interstitial lung disease does not automatically mean that a patient has developed permanent lung scarring.

“Influenza can, in some cases, trigger inflammatory conditions such as post-viral pneumonitis or organising pneumonia, which need to be distinguished from irreversible lung scarring,” Dr Agrawal said.

That distinction is important because the appearance of the lungs on a scan does not, by itself, tell the entire story about whether the changes will be permanent.

There is another pattern that Dr Agrawal is seeing, and it can be particularly deceptive.

He said, just as the patient begins to recover from influenza, fever comes down and the overall condition seems to improve, then several days later, the illness returns — this time with high fever, worsening cough, sputum and increasing difficulty in breathing.

Oxygen levels may begin to fall, and investigations may reveal pneumonia.

Dr Agrawal noted that this kind of “second deterioration” can point towards a secondary bacterial infection following influenza.

The influenza virus can damage the respiratory lining and weaken the lungs’ normal defence mechanisms, making it easier for bacteria to infect the respiratory tract.

“These are patients who may initially think that the flu is taking a little longer to settle. But when there is a second rise in fever, increasing cough, breathlessness or falling oxygen saturation, it should not be ignored,” he said.

In other words, the direction of the illness matters.

A cough that is gradually improving is one thing. A cough that is becoming more severe, particularly when accompanied by renewed fever or breathlessness, is another, pointed out Dr Agrawal.

He explained that influenza often starts suddenly. Fever, chills, headache, muscle aches, sore throat and cough are among its common symptoms. In many people, these begin to improve within a few days. But Dr Agrawal cautioned against simply waiting indefinitely for symptoms to disappear.

Persistent fever for six, seven or eight days, worsening cough, new-onset breathlessness or a fall in oxygen saturation should prompt medical evaluation, he said.

Similarly, someone who was clearly improving but suddenly developed a high fever again, productive cough or breathing difficulty should not assume that it is merely the same flu continuing.

“Any clear change in the trajectory of the illness needs attention,” is the larger message emerging from such cases.

One reason influenza can become serious is that the virus itself can cause pneumonia. In severe cases, extensive inflammation in the lungs can result in acute respiratory distress syndrome, in which the lungs struggle to provide enough oxygen to the body.

Such patients may require oxygen support, non-invasive ventilation or, in the most severe cases, mechanical ventilation.

But Dr Agrawal pointed out that not every prolonged cough after influenza means that a patient has developed severe lung damage.

Some people may develop airway inflammation and increased sensitivity after the infection. This can cause a dry cough, wheezing or chest tightness that continues for weeks even after the infection itself has settled.

The challenge, therefore, is knowing the difference between a lingering post-viral cough and signs of a complication.

Dr Agrawal said that older adults, young children and pregnant women are among those at greater risk of complications. The risk is also higher among people with conditions such as asthma, COPD, diabetes and heart disease, as well as those with obesity, cancer or weakened immunity.

But Dr Agrawal emphasised that serious influenza is not restricted to people with pre-existing illnesses.

Even a previously healthy person needs medical assessment if breathing becomes difficult, chest pain develops, oxygen levels fall or there is confusion, severe weakness, dehydration or coughing up blood.

“These warning signs should not be watched at home simply because the illness started as flu,” he cautioned.

Another concern, according to Dr Agrawal, is self-medication.

Because fever and cough can make patients fear a bacterial infection, antibiotics are sometimes started without medical advice.

But influenza is caused by a virus, and antibiotics do not treat the virus itself.

“Influenza is caused by a virus, so antibiotics do not treat the infection itself. They may be required if there is evidence or strong suspicion of a secondary bacterial infection,” he said.

Unnecessary antibiotic use, he emphasised, can contribute to antimicrobial resistance without helping the patient recover from influenza.

Steroids, too, should not become a routine response to flu symptoms. They may have a role in selected clinical situations but should be used only when prescribed by a doctor.

Antiviral medicines work best when started early, ideally within 48 hours of the onset of symptoms.

However, Dr Agrawal noted that the 48-hour window should not be interpreted as a reason for patients with severe disease to give up on seeking treatment if they present later.

Patients with severe or progressive illness, particularly those who are hospitalised or at high risk of complications, may still benefit from antiviral treatment even when they seek care after the first two days, explained.

The larger message, he emphasised, is not to create fear around seasonal influenza. “It is about recognising when the illness has stopped behaving like a routine flu and the virus moves beyond the upper respiratory tract, causes pneumonia, triggers significant inflammation or paves the way for a secondary bacterial infection.”