Mechanisms not understood

Even if patients show bronchial hyperresponsiveness, the eosinophilic inflammation typical of asthma is absent. Another possible mechanism for post-infectious cough is excessive mucus production due to inflammation of the airways. Secretions can accumulate and impair the cleansing function of the airway mucosa, the mucociliary clearance. In the case of persistent inflammation in the upper airways, especially in the nose and paranasal sinuses, secretions flowing down into the throat can directly activate the cough receptors and trigger the cough stimulus. The pathogenesis of post-infectious cough is multifactorial in most cases and varies from patient to patient.

If a patient complains of a cough that has persisted for at least three weeks, but no longer than eight weeks after an acute respiratory infection, a post-infectious cough may be present. After eight weeks, doctors speak of a chronic cough. If patients also experience blood in their sputum, systemic symptoms, difficulty swallowing, pronounced shortness of breath or hoarseness, it is essential that they inform their doctor of this during the consultation. These symptoms indicate a different and possibly more serious illness. In particular, more serious causes should be considered if patients have already had pneumonia in the past or smoke or have smoked heavily.

The doctor will only make a diagnosis of post-infectious cough if they have ruled out other possible causes such as the chronic respiratory diseases asthma and COPD and patients are not taking any medication that can cause a persistent cough, such as ACE inhibitors. It should also be borne in mind that gastro-oesophageal reflux can also act as a trigger factor for coughing. When the stomach pushes acid into the oesophagus, it can irritate nerves and trigger a cough.

A special form of post-infectious cough is caused by an infection with Bordetella pertussis (whooping cough pathogen). It can be a possible cause if the cough is paroxysmal and accompanied by a wheezing sound when breathing in (inspiratory stridor) or vomiting after coughing attacks. However, many doctors do not include whooping cough in the differential diagnosis of a persistent cough. After an incubation period of one to three weeks, this disease is followed by a flu-like phase lasting around two weeks and the cough worsens in the following weeks, often accompanied by the typical ‘wheezing sound’.

In children and adults, macrolide antibiotics such as azithromycin, clarithromycin or erythromycin are the drugs of choice for whooping cough. However, these can only prevent coughing if they are given in the early stages, before the bacteria have formed toxins. Later treatment is no longer as effective, as the toxin that has already formed can continue to cause the cough.

In post-infectious coughs following other infections, antibiotic therapy is ineffective if there is no bacterial cause. Sometimes bronchodilators such as inhaled ipratropium are prescribed to alleviate the symptoms. Inhaled glucocorticoids are intended to suppress inflammatory reactions and bronchial hyperresponsiveness, and in practice some patients seem to respond to them. In most cases, however, the cough is self-limiting and no medication is required.

Systematic reviews have also shown that there is no evidence for the benefit of inhaled glucocorticoids, bronchodilators such as salbutamol or antibiotics for post-infectious cough. Instead, these therapies are associated with adverse effects and high costs. They put a strain on supply chains and this can mean that inhalers are no longer sufficiently available for patients who really need them. Metered-dose inhalers also pollute the environment due to the propellants used. Scientists from Switzerland are currently investigating whether a five-day treatment with oral glucocorticoids brings patient-relevant benefits compared to placebo. There are already indications that the medication could improve cough-related quality of life and reduce the duration and intensity of post-infectious coughs.

The efficacy of centrally acting antitussives such as codeine and dextromethorphan in post-infectious coughs has not been proven. Cough suppressants suppress the urge to cough, but should only be taken for a short time to avoid side effects and addiction. Phytopharmaceuticals can supportively reduce the symptoms and promote healing. Thyme and ivy extract have anti-inflammatory and expectorant properties and are traditionally used to relieve coughs. Although the scientific evidence is not as good as for other preparations, many patients report an improvement in symptoms.

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