Diagnosing pneumonia in a hospital setting is relatively straight forward. The British Thoracic Society (BTS) have produced guidelines which tell us that in order to diagnose pneumonia in a patient in hospital they should have symptoms and signs of pneumonia PLUS new shadowing on a chest x-ray.
Symptoms and signs of pneumonia include:
- Shortness of breath
- Purulent sputum
- Chest pain
- Signs of consolidation – reduced expansion, dullness to percussion, bronchial breathing and increased tactile vocal fremitus or vocal resonance
This works very well in the hospital setting but in primary care it is not possible to get a chest x-ray quickly; so how should pneumonia be diagnosed in the community? Well the BTS have also provided a clinical definition for pneumonia in primary care:
- One other lower respiratory tract symptom (Shortness of breath, purulent sputum, chest pain)
- New focal chest signs on examination
- One systemic symptom (fever, sweats, shivers, aches & pains)
- NO OTHER EXPLANATION
It is worth noting that “crackles” in the chest are not a good sign of pneumonia and are usually due to some other pathology such as interstitial oedema, fibrosis or even pneumonitis, and many patients have crackles in their chests all of the time.
In order to diagnose pneumonia it is important to exclude a diagnosis of exacerbation of COPD (also known as non-pneumonic lower respiratory tract infection). Exacerbation of COPD is diagnosed by the patient having COPD PLUS increasing shortness of breath, cough, increased sputum production or change in sputum colour with no focal or systemic signs of pneumonia. Antibiotics may be indicated if the sputum is purulent but otherwise NICE recommends a supportive care approach for COPD patients.
Do sputum cultures help in pneumonia?
So having diagnosed pneumonia clinically is it worth sending a sputum sample to the microbiology laboratory? Okay, I know I’m biased because I’m a microbiologist, but I think there is a value in sending carefully taken sputum for culture (see how to spit and polish your diagnosis for how to interpret a sputum result). However a sputum sample will not help you diagnose pneumonia, as the results take 2-4 days to come back from the laboratory which is too long to wait and anyway a positive sputum culture is not part of the BTS diagnostic criteria! A sputum sample does however help you know what might be causing the pneumonia, whether the antibiotics you have prescribed are treating the cause, and if the antibiotics do not treat the cause or the patient is not improving then the result can help guide further treatment.
The most common causes of pneumonia are:
- Streptococcus pneumoniae
- Haemophilus influenzae
- Staphylococcus aureus
- Mycoplasma pneumoniae
- Legionella pneumophila (especially if travelled)
- Chlamydia pneumoniae
- Viruses e.g. Influenza Virus, Parainfluenza Virus, Respiratory Syncytial Virus (RSV), Adenovirus
In fact between them, S. pneumoniae (40%) and viruses (25%) cause two thirds of all community acquired pneumonias (CAP).
The BTS and the National Institute for Health and Care Excellence (NICE) recommend using Amoxicillin as first line therapy for CAP or Clarithromycin or Doxycycline if the patient is allergic to Beta-lactams. Watch out though as resistance to these antibiotics does occur in the common bacteria causing CAP and a sputum culture can help spot this.
There is excellent European surveillance for antibiotic resistance in S. pneumoniae, but for the other causes of CAP the data is based upon that seen within local laboratories or published articles in journals. Current resistance rates for S. pneumoniae in the UK are:
- Penicillins 0.5% (although 5% show reduced susceptibility even though they are not technically completely resistant, so called intermediate sensitivity)
- Macrolides e.g. Clarithromycin 7%
- Tetracyclines e.g. Doxycycline 5%
Resistance in Europe and a number of Mediterranean countries can be much higher, with up to 40% of S. pneumoniae being completely resistant to penicillin. Additionally in the UK, Amoxicillin resistance in H. influenzae is approximately 10% and in S. aureus it is over 85%.
If a microorganism is reported that is resistant to the antibiotic the patient has been given it doesn’t necessarily mean the antibiotic should be changed! WHAT isn’t that nonsensical?! Let me explain, the treatment only needs changing if the patient is not getting better. It might be that the causative bacteria is different to the one cultured (remember what is grown is not always causing the infection, it is just the colony that was picked from sample) or if the sputum sample was taken after antibiotics were started, the antibiotics may have killed off the causative sensitive bacteria leaving resistant bacteria behind which are then reported out by the laboratory.
However remember, if the patient is not improving then it is sensible to choose one of the other antibiotics reported to which the bacterium is sensitive!
So let’s examine empirical treatment strategies for CAP in primary care:
Scenario 1 – 67 year old man, no allergies
Treated with Amoxicillin for 7 days. Sputum culture confirmed S. pneumoniae sensitive to penicillins. Systemic symptoms resolved but cough persisted at 7 days. Reassure the patient that often the cough takes a bit longer to settle. The cough may be due to bronchial irritation from the infection or some residual inflammation that may take longer to resolve. The 7 days of antibiotics is usually enough to get rid of the bacterium.
Scenario 2 – 67 year old man, beta-lactam allergy
Treated with Clarithromycin. Sputum culture identified a S. pneumoniae resistant to Erythromycin. Therefore resistance to Clarithromycin can be implied from the Erythromycin resistance as they are the same class. The patient was not feeling any better and so they were switched to Doxycycline as the bacterium was reported sensitive to Tetracyclines (Doxycycline is a Tetracycline).
Scenario 3 – 67 year old man, beta-lactam allergy
Treated with Doxycycline. Sputum culture identified an H. influenzae resistant to tetracyclines. The bacterium was reported as sensitive to Amoxicillin and resistant to Clarithromycin. The patient cannot have the Amoxicillin due to their beta-lactam allergy but there are still options. If the beta-lactam allergy is not severe (e.g. rash) then an oral cephalosporin (Cefaclor, Cefradine, Cefalexin) could be used. If it is sensitive to Amoxicillin it will be sensitive to cephalosporins. Although they are beta-lactams, cephalosporins are not penicillins and are therefore less likely to cause an allergic reaction and they are more effective than the non-beta-lactam alternatives (Clarithromycin or Doxycycline). If the beta-lactam allergy is severe (e.g. anaphylaxis, angioedema or Stevens-Johnson reaction) then it is worth trying a fluoroquinolone antibiotic e.g. Levofloxacin to which the H. influenzae should be sensitive.
Scenario 4 – 67 year old man, no allergies
Treated with Amoxicillin for 7 days. Sputum culture identified an Amoxicillin resistant H. influenzae. However, on review the patient was feeling better and so there is no need to change the antibiotic. It is likely that either the H. influenzae was not the cause of the patient’s pneumonia or that the sputum sample was taken after the antibiotics were started and therefore the Amoxicillin may have killed off the causative sensitive bacterium leaving resistant H. influenzae behind.
Scenario 5 – 67 year old man, no allergies
Treated with Amoxicillin for 7 days. Sputum culture failed to identify a cause for the patient’s pneumonia. If the patient is feeling better then it may be that the cause was viral (25% of CAP is viral!) or the sputum was taken after the antibiotics were started and the antibiotic has killed off the cause of the pneumonia and stopped the laboratory being able to grow it. If the patient is still unwell then change the antibiotic to either Clarithromycin or Doxycycline and repeat the sputum culture, and maybe the laboratory will grow the cause this time. There is no need to send a viral screen as the results can be inconclusive and unhelpful for clinical decision making.
- The diagnosis of pneumonia in primary care is based upon a combination of symptoms and signs according to the BTS guidelines, whereas in hospital a chest x-ray is required
- Ask patients to give a sputum sample before they start any antibiotics
- Treatment of pneumonia in primary care is initially empirical with either Amoxicillin, Clarithromycin or Doxycycline
- A sputum sample can help guide the ongoing or future treatment of patients if an antibiotic resistant bacterium is isolated
Whatever microorganism is grown from the sputum sample it is important to look at the result in the context of the individual patient. If they are better a seemingly contradictory result does not necessarily need to change the patient’s treatment, however if the patient is no better or worse the culture result can indicate alternative antibiotics to prescribe.
P.S. my wife seems to have a new bout of “old moania”! By the way, does anyone know what the term double pneumonia actually means?