Acute bronchitis, tracheobronchitis, bronchiolitis

Acute bronchitis, tracheobronchitis, bronchiolitis

A cough that follows a viral infection of the large airways, and why most of it needs no antibiotic; with bronchiolitis, its small-airway counterpart in infants.

Acute bronchitis, from a virus to a lingering cough

3 scenes, 0:28

A film in three scenes on a white page. The lungs, seen from the front, are pale pink and see-through, with the branching airways inside them; with a few breaths, small dark teal virus particles are drawn down the windpipe and settle on the walls of the windpipe and the large bronchi, but not the small airways beyond, and those large airways turn from pale to pink-red as they become inflamed. A bronchus is cut open along its length: its wall shows in layers, with pale plates of cartilage on the outside, a band of rose smooth muscle and a peach lining carpeted with amber cilia that beat in waves under a thin violet layer of mucus. Virus particles land on the lining, and around each the cilia are lost, patch by patch, leaving bare peach patches; the mucus thickens into a violet mass with lumps in it, the wall swells and reddens, and the airway narrows. Then, over what stands for weeks, the swelling and redness go down, the mucus thins back to a film, and last of all the cilia grow back, patch by patch, until the lining is a carpet of beating cilia again.

0:00 / 0:28

A virus reaches the large airways

Scenes

About this film

A virus infects the lining of the trachea and bronchi. The lining is damaged and its cilia are lost, more mucus is made and the inflamed wall swells, so the patient coughs. The acute illness eases within days, but the lining takes weeks to repair, and while it does the airway stays oversensitive, which is why the cough lingers, usually for up to 3 weeks.

Simplified: not to scale: the virus particles drawn far larger than life, and the cilia far longer; one virus shown, while many viruses, and a few bacteria, cause acute bronchitis; the wall's layers simplified: the cartilage drawn as regular plates, the mucous glands and the blood vessels left out; the lining drawn as a smooth sheet of cells, and the white cells drawn into the inflamed wall left out; the extra mucus drawn as a thicker layer; in life it is coughed up as it is made; days of infection and weeks of repair squeezed into seconds.

6 sources
  1. Kumar and Clark's Clinical Medicine, 10th edition. Elsevier, 2021. Chapter 28, Respiratory disease: acute bronchitis (p. 954).
  2. Aagaard E, Gonzales R. Management of acute bronchitis in healthy adults. Infect Dis Clin North Am. 2004;18(4):919-37.
  3. Braman SS. Chronic cough due to acute bronchitis: ACCP evidence-based clinical practice guidelines. Chest. 2006;129(1 Suppl):95S-103S.
  4. Pickles RJ, DeVincenzo JP. Respiratory syncytial virus (RSV) and its propensity for causing bronchiolitis. J Pathol. 2015;235(2):266-76.
  5. Love ME, Proud D. Respiratory viral and bacterial exacerbations of COPD: the role of the airway epithelium. Cells. 2022;11(9):1416.
  6. Ying W et al. Research progress on the mechanisms of high mucus secretion in the airway: a scoping review. Int J Chron Obstruct Pulmon Dis. 2026;21:588363.
Contents6 sections

At a glance

  1. Acute bronchitis is a self-limiting infection of the large airways, almost always viral, whose main symptom is a cough. It is a diagnosis you reach after excluding pneumonia, asthma and a COPD exacerbation.
  2. Coloured sputum does not mean bacteria. The colour comes from white cells and shed airway cells, in viral and bacterial infection alike.
  3. The cough lasts about 18 days on average in healthy adults, usually outlasting the rest of the illness, which improves in 4 to 8 days.
  4. Antibiotics give healthy adults only a small benefit, about half a day less cough, with more side effects. No routine antibiotic, then: an immediate prescription for the systemically very unwell, and an immediate or back-up one considered for those at higher risk of complications.
  5. Bronchiolitis is the small-airway disease of infants, usually from respiratory syncytial virus (RSV). It is treated with oxygen and fluids, and it can now be prevented.

Definition and overview

Acute bronchitis is a self-limiting inflammation of the large airways, the bronchi, shown by a cough that lasts up to about three weeks, in a person with no pneumonia and no chronic lung disease. When the trachea is involved as well, usually with burning behind the sternum, it is called tracheobronchitis: the same illness, a little higher up the airway.

Bronchiolitis is the same kind of viral inflammation, lower down, in the bronchioles. It is mainly a disease of infants under two years, and in adults the word usually means something else, such as the obliterative bronchiolitis that follows a lung transplant.

Etiology and pathophysiology

Causes

Viruses cause most acute bronchitis: rhinoviruses, influenza A and B, parainfluenza viruses, RSV, coronaviruses (SARS-CoV-2 among them), adenovirus and human metapneumovirus. A minority is due to bacteria, chiefly Mycoplasma pneumoniae, Chlamydia pneumoniae and Bordetella pertussis, the cause of whooping cough. Streptococcus pneumoniae and Haemophilus influenzae often follow a viral infection as a secondary bacterial one, and are likelier in smokers and in people with COPD. Non-infectious irritants, such as smoke, dust and fumes, can cause a similar picture.

How the virus makes a cough

The virus infects the cells that line the airway and damages them, and the ciliated cells that sweep mucus up and out are among the first to go. The airway wall becomes inflamed and swollen, goblet cells pour out mucus, and the exposed sensory nerves of the airway become more easily set off by cold air, smoke or talking. Even when the virus is gone, repair is slow: the lining takes weeks to regrow, and the airway may stay twitchy and even wheezy for that long. That is why the cough outlasts the infection.

What the virus does to an infant's bronchioles

In bronchiolitis the virus, most often RSV, infects the cells lining the bronchioles. The infected cells lose their cilia, round up and are shed into the lumen, where they pile up with neutrophils into plugs, while oedema swells the wall and lymphocytes gather round it. An infant's bronchioles are so narrow that this is enough to block them. Air is trapped behind the plugs, so the chest overinflates; as the trapped air is absorbed, patches of lung collapse, ventilation and perfusion no longer match, and the infant becomes hypoxic.

An infant's bronchiole, healthy and in bronchiolitis
Two round fields of lung seen through a magnifier, side by side. In each, a small airway, a bronchiole, is cut across in the middle, surrounded by alveoli, the white air spaces between thin pink alveolar walls that carry small red capillaries. On the left, the healthy bronchiole: a round open lumen, lined by a ring of columnar peach-coloured cells with amber cilia that beat, two violet goblet cells among them, a thin pale wall and a thin ring of rose smooth muscle. On the right, the same airway in viral bronchiolitis: most of its lining cells have lost their cilia and the lining is ragged; the lumen is narrower and filled by a pale plug in which lie rounded, shed lining cells and pale blue neutrophils; the wall under the lining is swollen and washed pale teal with oedema, and a ring of small pale blue lymphocytes surrounds the outside of the airway.

Point at a name or a part to light it.

In infants, viruses, most often respiratory syncytial virus, infect the lining of the bronchioles, airways under 2 mm across. The infected cells lose their cilia and are shed, and with neutrophils they plug the lumen; oedema swells the wall and lymphocytes gather round it. Air is trapped behind the plugs on breathing out, and the chest hyperexpands.

Simplified: not to scale: the airway's wall drawn thicker than life so its layers read; far fewer alveoli, cells and capillaries than a real field holds, and every capillary drawn cut across; the lining drawn as one ring of columnar ciliated cells; the club cells, which the virus also infects, and the basal cells left out; the plug drawn as a few shed cells and neutrophils in a pale mass of mucus and fibrin; the changes, which are patchy, all drawn in one airway, and the healthy airway drawn without its thin mucus layer; the trapped air and the patches of collapsed alveoli beyond the plugged airway left out; the cilia's beat played far slower than life.

3 sources
  1. Kumar and Clark's Clinical Medicine, 10th edition. Elsevier, 2021. Respiratory syncytial virus infection (p. 521), and the airways (p. 930).
  2. Pickles RJ, DeVincenzo JP. Respiratory syncytial virus (RSV) and its propensity for causing bronchiolitis. J Pathol. 2015;235(2):266-76.
  3. Georgakopoulou VE, Pitiriga VC. Immunomodulation in respiratory syncytial virus infection: mechanisms, therapeutic targets, and clinical implications. Microorganisms. 2025;13(8):1876.

Clinical features

The illness opens with the features of a cold, then an irritating dry cough with a sore, raw feeling behind the breastbone. Over a few days the cough becomes productive, often of yellow or green sputum. There may be chest tightness, wheeze and breathlessness on exertion, and a mild fever for a few days.

On examination there are often a few scattered wheezes or coarse crackles that change with coughing. In a healthy adult, the pulse, respiratory rate and temperature are normal or only slightly raised, there is no area of dull percussion, and breath sounds are normal.

the average length of an acute cough
18days
for the illness to improve by itself in a healthy adult
4–8days
the point beyond which a cough that is not improving needs another look
3–4weeks

Bronchiolitis in infants

An infant with bronchiolitis has a cold for one to three days, then a cough, fast breathing, wheeze and fine crackles through both lungs. The chest is drawn in and the nostrils flare. Feeding gets hard because the infant cannot suck and breathe at once, and the youngest infants may stop breathing for short spells (apnoea).

Diagnosis and management

Diagnosis

The diagnosis is made at the bedside from a recent cold and a cough with normal vital signs. A chest X-ray is not needed unless pneumonia is suspected: a fast pulse or breathing rate, a fever above 38 °C, focal chest signs, or a patient who looks unwell. If it is unclear whether an antibiotic is needed, a point-of-care C-reactive protein (CRP) can help: below 20 mg/L, do not routinely offer an antibiotic; 20 to 100 mg/L, consider a back-up prescription; above 100 mg/L, offer an immediate one. The chest X-ray, not the CRP, is the test for suspected pneumonia. Sputum culture and viral swabs are not needed in an otherwise healthy adult.

Think of the other diagnoses with a cough, and of whooping cough in particular where the cough comes in paroxysms, with a whoop or vomiting after coughing, and lasts for two weeks or more. Bronchitis in a smoker with years of cough is COPD until shown otherwise.

Management in adults

  • Explain the course. Tell the patient that the cough usually settles within three to four weeks, and what would call for a review (breathlessness, fever that comes back or lasts, coughing blood).
  • Treat symptoms. Fluids, and paracetamol or ibuprofen for fever and aches. Cough medicines have little proven effect; honey is a sensible option for children over a year old. Bronchodilators and corticosteroids are not advised unless there is underlying airways disease such as asthma.
  • Stop smoking. Smokers recover more slowly.
  • Antibiotics only rarely. No routine antibiotic for people who are not very unwell and not at higher risk of complications. An immediate prescription is for those who are systemically very unwell; for those at higher risk of complications, an immediate or a back-up (delayed) prescription is considered. Higher risk means, for example, serious heart, lung, kidney or liver disease, cystic fibrosis, immunosuppression, or older age with other risk factors. The usual first choice in the UK is a five-day course of doxycycline (200 mg on the first day, then 100 mg a day), with amoxicillin, clarithromycin or erythromycin as alternatives; doxycycline is avoided in pregnancy and under 12 years, where amoxicillin is preferred.

Management of bronchiolitis

Bronchiolitis is a clinical diagnosis, with no routine X-ray, blood tests or viral swabs, and care is supportive. Oxygen is given when the saturation stays below 90 per cent in air (below 92 per cent in babies under 6 weeks and in children with an underlying condition such as heart or chronic lung disease), fluids by a nasogastric tube if the infant cannot feed enough, and nasal suction when secretions are causing distress or feeding difficulty, not routinely. For impending respiratory failure, CPAP is advised; high-flow nasal oxygen is widely used, but the trial results are mixed. Infants are admitted when they cannot feed (taking half to three-quarters of their usual feeds or less), have apnoea, are working hard to breathe, or when the parents cannot cope at home; prematurity, age under 3 months and congenital heart or chronic lung disease raise the risk. Hypertonic saline, bronchodilators, corticosteroids, antibiotics, adrenaline, montelukast and ipratropium are not advised, since they have not been shown to help.

Prevention of RSV illness now has two routes: a long-acting monoclonal antibody given to the infant (nirsevimab), and a vaccine given to the mother late in pregnancy, which passes antibodies to the baby.

Epidemiology

Acute bronchitis is among the most common reasons for an adult to see a doctor, mostly in autumn and winter, when respiratory viruses circulate. Because it is viral, antibiotics should rarely be needed, but they are still given often: in the United States, about seven in ten adult visits for acute bronchitis between 1996 and 2010 ended in an antibiotic prescription, and the rate rose over those years.

Bronchiolitis is the commonest lower respiratory infection of infancy. It peaks in the winter months in temperate countries. About one infant in three has it in the first year of life, and a few in a hundred are admitted to hospital. RSV causes most cases; the other causes are rhinovirus, parainfluenza viruses and human metapneumovirus.

Prognosis

Acute bronchitis in a healthy adult gets better by itself. The illness improves in 4 to 8 days, but the cough lasts about 18 days on average and usually settles within three to four weeks; a lingering "post-infectious" cough between three and eight weeks can follow. Complications are uncommon: pneumonia, and exacerbations of asthma or COPD in those who have them.

A cough that is not improving after three to four weeks needs a second look, with a chest X-ray, especially in a smoker or a person over 40, and cough beyond eight weeks is a chronic cough with its own work-up (asthma, reflux, upper-airway cough syndrome, drugs such as ACE inhibitors, and lung cancer).

Most infants with bronchiolitis recover within two to three weeks. A few need intensive care, mostly those born prematurely or with heart or lung disease. Recurrent wheeze is common in the following years, though whether bronchiolitis causes later asthma or marks children who were bound to develop it is still debated.

Check yourselfAnswer, then say how sure you were: a lucky guess still counts as a weak point.

1A healthy 30-year-old has had a cough for five days and now brings up green sputum. What does the colour tell you?

2Roughly how long does a cough from acute bronchitis last on average?

3Which finding in a patient with a cough points to pneumonia rather than acute bronchitis?

4What does the evidence say about antibiotics for acute bronchitis in otherwise healthy adults?

5A 4-month-old with bronchiolitis feeds poorly and has an oxygen saturation of 89 per cent in air. What is the mainstay of treatment?