Is a persistent cough a cause for worry? Doctors say it's not always linked to lung infection

SINGAPORE — You may have had this experience before: You have recovered from a cold or a flu but that pesky cough continues to linger. Not only is a nagging cough annoying, it can also be exhausting and cause broken sleep.

For some, a persistent cough may even be an alarm bell for something more serious such as lung cancer.

When is a persistent cough a cause for worry, and what can be done to relieve it?  

WHAT IS A PERSISTENT COUGH?

Coughing is a protective natural reflex intended to clear the airways of excessive secretions and foreign particles.

There are several reasons why some coughs persists for weeks or even months.

Dr Jessica Tan Han Ying said that a cough that lasts more than eight weeks in adults and more than four weeks in children is a “chronic cough”.

She is a senior consultant and head of department of respiratory medicine at Sengkang General Hospital (SKH).

Although there is no formal domestic data on chronic cough, doctors from SKH and Tan Tock Seng Hospital (TTSH) told TODAY that in recent years, they have observed an increase in patients suffering from persistent cough being referred to them.

Dr Tan from SKH estimated a 25 to 30 per cent increase in patients at the hospital seeking medical attention for prolonged cough, compared to the period before the Covid-19 pandemic. These cases may not always be related to a preceding Covid-19 infection.

Every month, Dr Tan Wei Jie from Dtap Clinic, a private clinic, sees around two to three patients with chronic cough requiring treatment.

“In my general practitioner practice, many older adults have chronic cough due to years of smoking, while the non-smokers may have underlying infections or heart conditions,” he said.

WHAT CAUSES CHRONIC COUGH

A long-lasting cough can also affect younger adults and in such cases, doctors said that there can be many reasons for its persistence.

1. INFECTION

Based on Dr Anna Lau’s experience, the most common cause of a persistent or chronic cough in younger adults is one that lingers after a viral infection such as Covid-19 or an upper airway cough syndrome.

Dr Lau is an associate consultant with TTSH’s department of respiratory and critical care medicine.

“After a viral infection, patients can also continue coughing for a fairly long period of time. This is due to the inflammatory cascade that was triggered by the previous infection, leading to hypersensitivity of the airway,” she explained.

An inflammatory cascade is a chain of reaction triggered by the body’s immune system when it detects something harmful such as an infection or injury.

However, this response can sometimes lead to increased sensitivity and prolonged inflammation, contributing to conditions such as a chronic cough.

2. MEDICATION

For people experiencing a persistent cough, it is also important to consider other possible causes not related to the lungs that may require a different course of treatment altogether, Dr Tan from Dtap Clinic said.

For example, a dry cough is commonly a reported side effect of certain medications used to control blood pressure.

3. NOSE

Allergic rhinitis is a type of inflammation in the nose that occurs when the immune system overreacts to allergens in the air.

It can cause a post-nasal drip, which can then make it hard to shake off a cough.

Excessive mucus may accumulate at the back of the throat and nasal passages, and “drip” down and irritate the throat, triggering a cough reflex, Dr Tan from SKH explained.

4. STOMACH

People who have chronic gastric problems may also have chronic cough. For those with gastroesophageal reflux disease (Gerd), stomach acid moves up into the oesophagus, the pipe connecting to the throat.

“Sometimes, acidic content may reach the throat and airways, irritating the lining of the throat and triggering a cough reflex as our body attempts to clear the irritation,” she added.

WHEN TO SEEK MEDICAL ATTENTION FOR A PERSISTENT COUGH

Dr Tan from SKH advised people to see a doctor if a cough persists eight weeks after a bout of acute respiratory infection.

Patients are generally advised to consult a general practitioner, who will make a referral to a specialist if needed.

However, Dr Tan from Dtap Clinic suggested seeing a doctor earlier if the cough does not improve after more than two weeks, and especially if there are more serious symptoms.

For example, if it is accompanied by shortness of breath, chest pain, prolonged fever, low energy or if the person is coughing out greenish or yellowish phlegm.

Other more serious symptoms include weight loss and coughing out blood.

“You don’t want to miss an important diagnosis that may jeopardise your health in the long term,” he said.

Studies have shown that patients whose coughs lasts a long time experience frustration, fatigue, interrupted sleep and impaired quality of life.

In a multi-centre study published in 2019 in Lung, a medical journal that covers pulmonary medicine, almost all of the patients reported that chronic cough substantially affected their daily lives, with the worst seen in those whose cough remains unexplained.

Dr Lau from TTSH said that chronic cough “is definitely something that burdens our patients greatly”.

“Without proper assessment and treatment of the underlying cause, the cough may not resolve. Managing the underlying cause is the key to managing chronic cough.”

WHY IDENTIFYING ROOT CAUSE OF CHRONIC COUGH IS VITAL

Treating the symptoms without identifying the root cause of the chronic cough may potentially result in a worsening of symptoms due to complications or missing out an important diagnosis that may be life-threatening, Dr Tan from Dtap Clinic said.

To diagnose the underlying cause, the doctor typically takes into account the thorough history of the symptoms, followed by performing a full physical examination, he added.

This includes taking temperature, looking in the throat and listening to the lungs and heart.

“Based on the symptoms presented and the examination findings, we would then be able to come up with a preliminary diagnosis and advise on the appropriate treatment.

“For some cases of persistent cough, doctors may order a chest X-ray to further evaluate the condition,” he said. 

CAN A CHEST X-RAY ALONE GIVE A DIAGNOSIS?

In general, all patients with chronic cough at TTSH’s respiratory clinic undergo a chest X-ray, Dr Lau said.

“Chest radiograph (X-ray) is easily available and is a good screening test for any major and significant lung abnormality such as lung mass or any signs of chronic lung disease.

“But more often than not, we will not be able to come to a diagnosis with just a chest X-ray alone,” she added.

Further investigations may be carried out. For example, a lung function test may be done if airway disease such as asthma is a concern.

A computed tomography (CT) scan of the thorax — the part of the body below the neck and above the waist — may be used in selective cases where diagnoses such as bronchiectasis, interstitial lung disease or lung cancer are suspected, Dr Tan from SKH said.

A culture and analysis of a patient’s sputum or fluids connected to the lungs may be used to detect infections such as pulmonary tuberculosis.

Depending on the cause of the cough, treatments vary.

For example, with asthma, inhaled corticosteroids may be used, whereas people who have gastric reflux may be asked to modify their diet and prescribed medications that suppress gastric acid production, she added.

Dr Lau from TTSH said that there are also some cases where there is no identifiable cause, and this is known as idiopathic chronic cough.

“In this group of patients, we will consider medications that act directly on nerves.”  

An idiopathic chronic cough is uncommon and this diagnosis is made only if the physician is unable to identify any cause, despite extensive investigation. Dr Lau added.

It is not related to any psychological condition and not psychologically induced.

HOW TO MANAGE A CHRONIC COUGH

For people suffering from a lingering cough, the doctors gave general tips on how to manage it at home:

• Stop smoking if one is an active smoker
• Avoid irritants that can induce or worsen cough, such as strong odours or chemicals
• Stay up to date with immunisations, such as getting a yearly influenza vaccination
• When sleeping, ensure the head is laid higher than the body, if the cough is related to post-nasal drip and it worsens when lying flat
• Do the same if you have gastric reflux and refrain from eating two hours before bedtime
• Maintain a balanced diet and exercise regularly to boost immune system
• Over-the-counter remedies such as cough drops, lozenges or cough syrups may provide some relief
• See a doctor if the cough is not improving or there are other symptoms of concern