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Four reasons why clinical severity scores should not be used on their own to guide antibiotic decisions in pneumonia.
Reading time: 10 minutes
Did you know that initial antibiotic prescriptions for community acquired pneumonia (CAP) are predominantly made by non-respiratory specialists in > 95% of the cases?
Introduction
We often prescribe antibiotics without knowing the causative organism. This is because cultures are usually negative and if positive, take a long time to come back. Antibiotic choice is therefore largely empirical (read ‘best guess’). Having a simple method to help guide this decision will be very valuable.
Enter clinical severity scores which were originally designed to predict the 30 day mortality in CAP. Their use was then extended to making decisions on the choice of antibiotics. It was based on the logic that high severity CAP would need broad-spectrum antibiotics and vice-versa. Real-world data unfortunately does not conform to this view. I shall now give you four reasons why this is the case.
1. There are no severity scores that can reliably predict the causative organism.
A few scores include risk factors like age that can sometimes point to the aetiology e.g. pneumococcus but this is insufficient.
2. Atypical bacteria are more frequent in the low severity group who are often treated in primary
care or out-patients.
The British Thoracic Scoiety (BTS) guidelines for example, do not offer a macrolide for atypicals to this group unless penicillin-allergic.
3. The CURB-65 score under-estimates the severity of illness in younger patients.
In fact, one study showed that nearly 40% of the patients classed as low severity had additional markers of severity like hypoxemia, multilobar consolidation etc.
4. CURB-65 over-estimates the severity of illness in older patients.
Most of them score with age alone which makes it very easy to cross the cut-off for high severity. This exposes them to unnecessary broad-spectrum antibiotics, bearing in mind that this group is already prone to a higher incidence of Clostridium difficile.
Advantages of Clinical Severity Scores
On the other hand, severity scores are simple to use making them easily accessible to non-respiratory physicians. However, it is worth bearing in mind that there are a host of other factors that need to be considered before deciding which antibiotic to use. In fact, ERS guidelines suggest 10 factors to consider before choosing an antibiotic (1). They are as follows:
- Age
- General prognosis e.g. is CAP part of a terminal illness?
- Previous hospitalisation < 3 months ago or repeated courses of antibiotics recently.
- Risk factors for immuno-suppression
- Severity e.g. CURB-65, pneumonia severity index, hypoxemia, multi-lobar consolidation
- Co-morbidity e.g. on dialysis, chronic lung disease like bronchiectasis or COPD
- Residence e.g. nursing home
- Aspiration and risk factors thereof
- Regional and local microbiological resistance patterns
- Patient factors like allergies, tolerability, inability to take oral medications etc.
In this day and age where we are fast running out of antibiotic choices, we need to be more circumspect in our approach at picking one. It is a question of balancing under-treatment, resulting in treatment failure and mortality against over-treatment causing resistant pathogens and hospital acquired infections to emerge.
In short, it is your overall assessment of the patient that helps you chose an antibiotic and not just a single score.
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medbookprof
I'm a Consultant Pulmonologist having experienced medicine first-hand across two continents stretching from the South Indian peninsula to the British Isles, the emerald nation of Ireland, to the Mediterranean climes of Italy and to the happiest country on earth, Denmark. Along the way, I have served as an honorary Associate Clinical Teacher and Royal College Associate tutor at University Hospital of Wales, collected a Masters in Medical Education and a passion for teaching. My enthusiasm is matched only by my thirst for simplifying clinical knowledge for medical students and making it accessible on a global scale.