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Mythbuster: ‘I’ve got my usual cough – it’s gone to my chest with green phlegm, so I need antibiotics’

Mythbuster: ‘I’ve got my usual cough – it’s gone to my chest with green phlegm, so I need antibiotics’

Debunking common patient myths and misconceptions: ‘I’ve got my usual cough – it’s gone to my chest with green phlegm, so I need antibiotics’

This statement illustrates one of two common presentations with a cough, alongside the newly named ‘Schrödinger’s cough’ (a cough at once so bad as to need antibiotics, and so mild that the person feels no need to test for Covid-19 and self-isolate). The belief that a cough with green or yellow phlegm has ‘gone to the chest’ and needs antibiotics is one of the most pervasive myths around. 

The reality 
Deciding whether a patient has a bacterial or viral infection is not as simple as ‘white phlegm = viral; green phlegm = bacterial’.

NICE defines acute bronchitis as ‘a lower respiratory tract infection which causes inflammation in the bronchial airways’.1 Around 44 per 1,000 adults will get acute bronchitis every year, usually caused by a viral infection. Common viruses include rhinovirus, enterovirus, influenza and coronavirus. 

Conversely, pneumonia, defined as ‘an infection of the lung tissue in which the air sacs… become filled with microorganisms… affecting the function of the lungs’, is usually caused by a bacterial infection and does need antibiotics.1 But pneumonia is much less common, affecting 5 to 10 per 1,000 people per year. Both bronchitis and pneumonia are more common in the winter. 

Deciding whether a patient with a cough has a bacterial or viral infection is not simple, even though the general public (and some healthcare professionals) seem to think it is. We need to look at the whole patient and make a holistic assessment. 

A patient with pneumonia is likely to be more unwell than one with acute bronchitis. They may have constitutional symptoms such as shivering, fever and body aches, and there may be focal chest signs such as decreased chest sounds, dullness to percussion or coarse crackles. Older people may present with confusion as their main clinical sign, and are less likely to spike a temperature. 

The CRB-65 score may be useful – one point is given for each of Confusion, Raised respiratory rate (≥30 breaths/minute), low Blood pressure (diastolic ≤60 mmHg or systolic ≤90 mmHg) and age 65 or more. Scoring zero gives the patient a less than 1% risk of dying from their infection, rising to 1-10% with a score of 1-2, and more than 10% for a score of 3-4. 

In primary care we largely use clinical judgment to make our decisions, although a sputum culture may be indicated if the infection seems moderately severe, or a chest X-ray if underlying pathology (such as lung cancer) is suspected. Neither of these investigations will deliver immediate results. 

It is important to remember that not all cough is caused by infection. Be alert for other causes, such as asthma, bronchiectasis, lung cancer, interstitial lung disease and foreign-body inhalation. 

The best approach 
With antibiotic resistance on the rise, it is vital that all healthcare professionals stand up to patients who demand an inappropriate prescription.

So, how should we manage the person with a new cough with coloured phlegm? Anyone severely ill should be considered for same-day hospital review, where a decision on admission will be made. Most of those not admitted should not be offered an antibiotic. 

The patient can be told that the cough is likely to last for three to four weeks and that taking an antibiotic is likely to shorten the symptoms by only about half a day, while putting them at risk of side-effects such as diarrhoea and nausea, and future antibiotic resistance.2 This can be backed up with a patient information leaflet.3,4 It is also good to use this opportunity to promote smoking cessation where appropriate. 

In medical school, I was taught that in multiple choice questions, options containing the words ‘always’ or ‘never’ were likely to be wrong, as general medicine is rarely so black and white. The same applies to a decision not to give antibiotics to a coughing patient, as there are cases where one is indicated. A common example is the patient with COPD, for whom increased sputum volume and purulence is a sign of an acute exacerbation for which NICE advises consideration of both oral steroids and antibiotics, specifically taking into account colour changes in the sputum when deciding on antibiotics.5 

It is also suggested that we ‘consider’ an immediate or back-up antibiotic prescription for people who are at higher risk of complications. These include:1 

  • Those with a pre-existing condition affecting the heart, lungs, kidneys or liver. 
  • Those who are immunosuppressed. 
  • Those with neuromuscular disease. 

This also applies to patients over 80 with more than one of the following conditions (two or more in over-65s):

  • Diabetes mellitus
  • Admission in the previous year 
  • History of congestive heart failure
  • Current use of oral steroids.

Some areas have access to point-of-care testing for C-Reactive protein (CRP), which identifies if there is inflammation in the body. A CRP of <20 mg/L can be used to reinforce a decision not to give antibiotics. If the CRP is 20-100 mg/L a delayed prescription might be given; a patient with a CRP of >100 mg/L will need antibiotics. 

In summary, the colour of the sputum does not usually inform the need for antibiotics, except in COPD. With the prospect that without urgent action we may be heading for a post-antibiotic era,6 it is vital all healthcare professionals stand up to demands for inappropriate antibiotics. If we all sing from the same hymn sheet then, slowly but surely, we can conquer this urban myth. 


  1. NICE CKS. Chest infections – adult. 2021. Link
  2. NICE CKS. Cough. 2021. Link
  3. RCGP. Treating Your Respiratory Tract Infection patient leaflet. Link
  4. Patient. Information on cough. Link
  5. NICE CKS. Scenario: Acute exacerbation of COPD. Link
  6.  WHO. Antibiotic resistance. Link 

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