A cough that won’t go away: first sort out what needs dealing with now from what needs looking into slowly

The virus has damaged the lining of the airways, and even once it has been cleared the airways have not got their normal sensitivity back, so the slightest irritation sets off a cough. This is the commonest cause of a subacute cough.

Clues: it clearly began with a cold, it is easing week by week, and there are no other symptoms. Most settle on their own within 3–8 weeks, with no need for an antibiotic.

Secretions from the nose or sinuses run back into the throat and keep irritating the cough receptors. In Taiwan it overlaps heavily with allergic rhinitis.

Clues: frequent throat clearing, a feeling of something in the throat, a blocked or running nose, coughing particularly after lying down or on waking, a history of nasal allergy.

Asthma does not always make you wheeze. There is a form of asthma in which the only symptom is a cough, particularly at night and in the early morning. It responds very well to inhaled corticosteroids, but is often put down to “a weak constitution” and dragged out for years.

Clues: coughing at night or in the early morning, coughing after exercise, brought on by cold air or cooking fumes, seasonal, an allergic constitution or a family history. Lung function may be completely normal — which is also why it is easily missed.

Acid, or non-acid stomach contents, flow back and irritate the lower oesophagus, setting off a cough through a nerve reflex. A substantial proportion of people have no heartburn at all — only the cough.

Clues: coughing after meals or on lying down, coughing after talking for a while, hoarseness, a sour taste or a feeling of something in the throat. A trial of treatment usually takes weeks to months before any effect shows, so do not give up after a fortnight of no change.

The names end in -pril (captopril, enalapril, ramipril and so on). It happens in about 5–20% of people, is commoner in women, and may only appear weeks to months after the drug is started, which is why so many people do not connect it with the medicine.

Clues: a dry cough, an itchy throat, no phlegm. Do not stop the medicine on your own — take the packet to the doctor who prescribed it; switching to an ARB usually settles it, and blood pressure control must not be interrupted.

In anyone with long-term smoking or exposure to cooking fumes or dust, a cough with phlegm should bring COPD to mind. It needs lung function testing to confirm, and cannot be diagnosed from symptoms alone.

Clues: aged over 40, a history of smoking or second-hand smoke, a morning cough with phlegm, progressively more breathless on exertion.

Taiwan is still a country with an intermediate tuberculosis burden. A cough lasting more than three weeks is itself one of the screening indicators for tuberculosis, and early tuberculosis may cause nothing but a cough, with no fever.

Clues: cough > 3 weeks, weight loss, night sweats, poor appetite, a contact history. A chest X-ray is the first-line tool, with sputum tests if needed.

Lung cancer accounts for only a small share of chronic coughs, but it is the one that costs the most to miss. A substantial proportion of lung cancer in Taiwan occurs in people who have never smoked, particularly women, so “I don’t smoke” cannot be used as a reason to rule it out.

Clues: a change in the character of the cough, coughing up blood, weight loss, hoarseness, repeated pneumonia in the same place, lung cancer in a first-degree relative.

Repeated infection permanently widens and distorts the bronchi, phlegm can no longer be cleared properly, and a cycle of cough — infection — more damage sets in.

Clues: phlegm every day, a large volume of it, repeated pneumonia in the same place, a past history of tuberculosis or whooping cough. A high-resolution CT of the chest is needed to confirm it.

A dry cough together with breathlessness on exertion is the classic combination in interstitial lung disease. On listening to the chest there may be crackles at the lung bases like Velcro being pulled apart.

Clues: a persistent dry cough, breathlessness after exertion, thickened finger ends (clubbing), a history of autoimmune disease, exposure to dust or to bird feathers.

In people who still cough after full investigation and treatment, this is now thought to be a hypersensitive cough reflex — a problem at the level of the nerves, rather than “no cause to be found”.

Clues: coughing on talking, laughing, smelling perfume or breathing cold air; a tickle in the throat first, then the cough. Cough suppression training from a speech therapist has evidence behind it, and some neuromodulatory drugs have a part to play too.