Overview
Predominantly dry cough, often lasting 3-8 weeks
Often occurs after a viral infection
Symptomatic treatment with short-term medication, but physical therapy may also be attempted
Most often resolves spontaneously, but some may develop a chronic cough.
Definition
Post-infectious cough is a cough that persists after the acute phase of a respiratory infection has disappeared, usually for 3 to 8 weeks, with no obvious abnormality on chest X-ray [1].
Post-infectious cough is the most common cause of subacute cough (3-8 weeks duration) [2].
Morbidity
There are no authoritative statistics on the incidence of post-infectious cough.
Some data show that about 81% of patients with acute upper respiratory viruses have cough symptoms, 69% have a cough that lasts longer than other infectious symptoms, and 4% have a cough that lasts longer than 4 weeks after other infectious symptoms have disappeared [3].
Etiology
Pathogenesis
Post-infectious cough often occurs after acute respiratory tract infections, and post-infectious cough manifestations may occur with various pathogen infections, such as viral, bacterial, and atypical pathogen (e.g., Mycoplasma pneumoniae, Chlamydia pneumoniae) infections.
Clinically, viral infections, such as rhinovirus, respiratory syncytial virus, coronavirus, influenza virus and parainfluenza virus, are most common [4].
Predisposing factors
Patients with a past history of post-infectious cough and increased cough sensitivity are more likely to develop it.
Cough can be triggered by exposure to changes in ambient temperature, deep breathing, laughing, and talking in this group of patients.
Pathogenesis
The respiratory mucosa is lined with sensitive vagal afferent fibers that innervate the airway, and these fibers are activated to cause a cough reflex. When the respiratory tract is infected, the cough reflex is more likely to be triggered.
On the one hand, infection triggers an immune response, which stimulates the release of inflammatory mediators from the body’s inflammatory cells, and also causes an increase in CNS excitability, leading to an increase in the sensitivity of the cough center.
On the other hand, infection can cause respiratory mucosal edema, airway smooth muscle contraction, etc., which can lead to increased cough sensitivity of the peripheral nerves, which makes it easy to cough, or an increase in the frequency of coughing and a more violent cough [4-5].
The above changes may remain for some time after the infection has disappeared, leading to a susceptibility to coughing that may also occur after the infection.
Symptoms.
Symptoms of post-infection cough are simple, with a predominantly dry cough, which may sometimes be accompanied by coughing up white sputum and a tickle in the throat, and usually without serious complications.
Main Symptoms
Cough
Post-infectious cough is often characterized by an irritating dry cough, mainly during the day.
Post-infectious cough may be exacerbated by significant changes in temperature, deep breathing, talking, and swallowing irritating foods [6].
The dry cough may also gradually resolve on its own over time.
Other symptoms
Coughing up sputum
Sometimes a small amount of white mucus sputum is coughed up, usually not yellow pus sputum.
Itchy throat
Sometimes accompanied by an itchy throat, which may resolve gradually over time.
Consultation
Department of Medicine
Respiratory Medicine
If a persistent, unexplained cough develops after an infectious disease has been cured, it is advisable to consult a respiratory physician.
Pediatrics
Minor patients can visit the Department of Pediatrics.
Preparation for medical treatment
Preparing for the consultation: registration, preparation of documents, common problems
Tips
Avoid taking cough suppressants on your own before going to the doctor to avoid influencing the doctor’s judgment of the condition.
It is recommended to wear loose-fitting clothes and avoid wearing clothes made of metal, so as to facilitate medical checkups or examinations.
Patients who are pregnant or preparing for pregnancy should inform the doctor in time.
Preparation List
Symptom list
Especially focus on the time of onset of symptoms, special manifestations, etc.
Is there fever? What is the highest degree?
How long have you been coughing? Is it a daytime or nighttime cough? Are there any triggers for the worsening of the cough, such as talking, laughing, exposure to cold air? How is it relieved?
Is there coughing up of sputum? What does the sputum look like?
Is there acid reflux or heartburn?
Is there any backflow of nasal secretions into the pharynx?
Medical History Checklist
Test results for the last 6 months to bring to the doctor’s office
Any recent cold or overexertion?
What kind of work do you usually do? What is the working environment? Any recent exposure to allergens?
Any recent infectious diseases of the respiratory system such as colds, pneumonia, etc.?
Any previous chronic respiratory or heart disease, such as chronic bronchitis, chronic obstructive pulmonary disease, chronic heart failure, etc.?
Any psychiatric system diseases, such as anxiety, depressive state?
Checklist
Test results in the last six months, which can be brought to the doctor’s office
Laboratory tests: routine blood test, C-reactive protein, allergen screening, induced sputum cytology
Imaging tests: Chest X-ray or Chest CT.
Pulmonary function tests: pulmonary ventilation function test, airway provocation test.
Others: echocardiography, electronic nasopharyngoscopy, gastric acid PH measurement or gastroscopy.
List of medications used
Medication used in the last 3 months, if available, bring the box or package with you to the doctor’s office
Glucocorticosteroids: e.g. budesonide aerosol, beclomethasone, prednisone acetate, etc.
Bronchodilators: e.g. formoterol, salmeterol, terbutaline, etc.
Leukotriene receptor antagonists: e.g. montelukast.
Acid-suppressing drugs: e.g. omeprazole, rabeprazole, voronasan, etc.
Antihistamines: e.g. loratadine, cetirizine, ebastine, etc.
Cough suppressants: e.g. codeine, dextromethorphan, etc.
Diagnosis
The diagnosis of post-infectious cough needs to be analyzed in conjunction with the history, symptoms, and relevant medical tests, and to exclude some other diseases that cause cough.
Diagnosis is based on
Medical history
The patient had an acute respiratory infection 3-8 weeks ago, and other acute symptoms have disappeared, but the cough is still prolonged.
Clinical manifestations
Symptoms
Irritating dry cough or a small amount of white mucous sputum, with or without pharyngeal tickling, most often during the day, which may be exacerbated by exposure to changes in ambient temperature, deep breathing, talking, or swallowing irritating foods.
Physical signs
There are no abnormal physical signs.
Laboratory Tests
Blood tests
Routine blood tests: white blood cells, neutrophils and lymphocytes are normal when coughing after infection. However, the presence of infection can be further determined.
Allergen screening: Serum antibodies such as immunoglobulin (IgE) test can be performed to find out if the patient has allergies.
Induced sputum cytology
The proportion of eosinophils in the induced sputum cells is more than 2.5%, suggesting the possibility of eosinophilic bronchitis.
Chest imaging
Includes chest X-ray or chest CT to assist in ruling out cough due to organic lung pathology.
Bronchoscopy
Often not used as a routine test for post-infectious cough, but can be used to assist in the diagnosis of cough due to airway disease, such as bronchopulmonary cancer, bronchial tuberculosis, and bronchial foreign bodies.
Lung function tests
It mainly includes pulmonary ventilation function test and bronchial provocation test, which are commonly used in the diagnosis of patients with clinical suspicion of asthma.
Nitric Oxide Measurement of Transoral Exhaled Breath (FeNO)
Elevated FeNO level (>50ppb) suggests eosinophilic airway inflammation, which may be associated with bronchial asthma, eosinophilic bronchitis and other diseases.
Diagnostic criteria
According to the 2021 guidelines for the diagnosis and treatment of cough [1], when the cough remains prolonged and persists for 3-8 weeks after the acute phase symptoms of respiratory infection have disappeared, and there is no obvious abnormality on X-ray chest examination, the diagnosis of post-infectious cough can be confirmed after excluding other diseases.
Differential diagnosis
Postnasal drip syndrome
Similarities
Patients with postnasal drip syndrome may have a history of acute upper respiratory tract infection prior to the onset of the disease, which may manifest as a subacute cough with no obvious abnormalities on chest imaging.
Differences
Patients often have chronic underlying nasal diseases, such as seasonal allergic rhinitis, perennial non-allergic rhinitis, and paranasal sinusitis. Symptoms can be relieved by targeted treatment of the underlying nasal diseases.
In addition to coughing and sputum, patients often complain of pharyngeal drip flu, mucus adherence in the oropharynx, nasal congestion, runny nose, sneezing and so on.
Examination reveals mucus adherence and cobblestone-like manifestations in the posterior pharyngeal wall or nasopharynx.
Cough variant asthma
Similarities
Both may present with a subacute cough and no significant abnormalities on chest imaging.
Differences
Cough variant asthma is characterized by prolonged, intractable dry cough, with more episodes at night or in the morning, often triggered by inhalation of irritating odors, cold air, exposure to allergens, strenuous exercise, or respiratory tract infections.
Lung function may show small airway dysfunction, elevated airway resistance; positive airway provocation test.
The application of cough suppressant drugs is ineffective, and standardized inhaled glucocorticoids and β2 agonists are needed to improve the condition [7].
Eosinophilic Bronchitis
Similarities
Both may present with subacute cough and no obvious abnormalities on chest imaging.
Differences
Eosinophilic bronchitis is characterized by airway eosinophilic infiltration, which is induced in some patients by irritating odors, cold air, and contact with allergens.
The proportion of induced sputum eosinophils was ≥2.5%; lung function was basically normal, and the day-to-day variability of PEF was normal; airway provocation test was negative.
Application of cough suppressants, antibiotics, bronchodilators were ineffective, oral or inhaled glucocorticoids were effective [8].
Treatment
Therapeutic purpose: post-infectious cough is generally self-limiting, and the therapeutic purpose is mainly to inhibit airway inflammation, alleviate symptoms and shorten the course of the disease to a certain extent [9-10].
Treatment principle: symptomatic treatment is the main focus, according to the nature of the cough to choose appropriate cough suppressants or expectorant drugs, should not be routinely used antibacterial drugs [9].
General treatment
Smoking cessation
Smokers should quit smoking, those who are difficult to quit smoking quickly can reduce smoking, and non-smokers should try to avoid inhaling “second-hand smoke”.
Improve the living environment
Drink plenty of warm water.
Take throat lozenges.
Avoid catching cold.
Avoid inhaling harmful particles, dust and irritating gases, and pay attention to indoor cleaning and ventilation.
Physical therapy
When there is a persistent dry cough, try controlled breathing. Place one hand on your chest and the other on your abdomen and slowly breathe in through your nose and out through your mouth, making your breathing as slow, relaxed and smooth as possible.
Coughing can also be relieved with the Stop Coughing Exercise. As soon as you feel the urge to cough, try closing your mouth and swallowing at the same time. Hold your breath for a few moments, then breathe out and in gently through your nose.
Medication
Antibacterial drugs are not necessary for coughing after viral infections. Short-term application of cough suppressants, antihistamines/decongestants, etc. is recommended for some people with significant cough symptoms, and expectorant drugs may be applied for those with combined sputum [10].
Cough suppressants
Mild cough generally does not require pharmacological intervention, if the cough is severe enough to interfere with life and sleep, cough suppressants can be applied appropriately, including the use of central cough suppressants alone, or an appropriate combination of antihistamines and decongestants (A/D preparations).
Central cough suppressants
Codeine
Directly inhibit the medullary center, cough effect is strong and rapid, but also has analgesic, sedative effect.
Mostly used for severe dry cough and irritating cough, especially dry cough with chest pain.
Has a certain degree of addiction, leading to drug dependence. Pregnant and lactating women should be cautious.
Dextromethorphan
Currently the most widely used cough suppressant in clinical practice, the effect of cough suppressant is similar to that of codeine, but there is no significant inhibition of the respiratory center, and it is not addictive.
Contraindicated in women within 3 months of pregnancy, lactating women and those with a history of psychosis. Use with caution in asthma, phlegm or hepatic insufficiency.
Peripheral cough suppressants
The commonly used drug is Narcotin.
Narcotine is an isovarine alkaloid contained in opioids, with effects comparable to those of codeine, no dependence, no inhibitory effect on the respiratory center, and is indicated for coughs of different causes.
First-generation antihistamines/decongestants (A/D preparations)
Meimin Pseudomallei Oral Solution
It is a compound preparation containing pseudoephedrine hydrochloride (which can eliminate nasal and pharyngeal mucosal congestion), dextromethorphan hydrobromide (which acts on the medullary center to inhibit coughing) and chlorpheniramine maleate (antihistamine).
A small number of patients may experience drowsiness, dizziness, palpitations, etc., which disappear on their own after stopping the drug. Therefore, driving locomotives, ships, engaged in aerial work, mechanical work is prohibited during work. It is prohibited for women within 3 months of pregnancy.
Compound Methenamine Capsules
This product is a compound preparation containing Methoxyphenamine Hydrochloride (inhibits bronchospasm and relieves coughing episodes), Narcotine (inhibits coughing), Aminophylline (inhibits bronchospasm and bronchial mucous membrane swelling), and Chlorpheniramine Maleate (antihistamine effect).
Contraindicated in lactating women and used with caution in pregnancy.
Expectorant drugs
Guaiacol glyceryl ether
It can stimulate the gastric mucosa, reflexively cause the increase of airway secretion, reduce the viscosity of sputum, and have certain bronchodilator effect to achieve the effect of enhancing mucus discharge.
Myrtle Oil
Extract of myrtle leaves, the main components include eucalyptus oil essence, limonene and α-pinene, can promote the airway and sinus mucosal cilia movement, thus promoting the discharge of sputum.
Ambroxol
It is a mucolytic agent, which reduces the viscosity of secretions and promotes ciliary movement to achieve expectorant effect.
Acetylcysteine
Acetylcysteine has an expectorant effect by disrupting the disulfide bonds of mucus glycoprotein polypeptide chains, reducing the viscosity of sputum, and antioxidant effect.
Carbocysteine
Carbocysteine can break the disulfide bond of mucin, thus reducing the viscosity of secretion.
Antimicrobials
Antimicrobials are required only when there are clear signs of bacterial infection, such as purulent sputum, or positive sputum culture results.
Cephalosporin antibiotics, e.g., ceftriaxone; quinolones, e.g., levofloxacin; and macrolides, e.g., azithromycin, may be chosen as needed.
Others
Routine application of inhaled glucocorticoids, montelukast, is not recommended for the treatment of post-infectious cough [1].
However, for cough after neocoronavirus infection, the addition of inhaled glucocorticosteroids can be considered to inhibit the inflammatory response, which can effectively relieve patients’ cough symptoms [9].
Prognosis
Cure
Most of the post-infectious coughs are self-limiting, and most of the patients’ symptoms can be relieved on their own in 3-8 weeks.
There are also some patients with persistent cough, and even develop chronic cough [9].
Daily
Daily management
Dietary management
Enhance nutrition, light and easily digestible diet, increase the intake of high quality protein such as eggs, lean meat and fish.
Life management
Quit smoking.
Regularize daily life, ensure good sleep and happy mood.
Take appropriate physical exercise.
Take medication regularly during treatment, do not reduce or stop medication on your own, and do not use unauthorized prescriptions.
Improve the living environment and avoid inhaling harmful particles and dust as much as possible.
Prevention
Avoid rain and cold to reduce the occurrence of upper respiratory tract infections.
Get vaccinated with influenza vaccine, new coronavirus vaccine, pneumococcal vaccine, etc. on the advice of medical personnel.
Pay attention to balanced nutrition and regular work and rest.
Exercise properly to improve body resistance.