Friday, 30 November 2018

Making a Diagnosis of Lower Respiratory Tract Infection in Children

This is one of the most common and difficult calls in General Practice, Emergency Medicine and acute Paediatrics: when to treat a child as a lower respiratory tract infection.  It's important because we don't want to miss a diagnosis of LRTI/ pneumonia, yet overtreating is bad medicine.  It's difficult because most children with an upper respiratory tract infection will have a cough and fever, and because the parents will be worried about the possibility of LRTI.  To make things worse, any child with uncomplicated URTI could later develop LRTI.  Not often, but often enough that it can influence our decision making.  So how do we get it right?

I think that it is a question of rule in/ rule out.  There are many elements to the assessment but there is one feature that determines whether the default is to assume that there is no LRTI and whether the default is to assume that there is a LRTI.  That feature is respiratory abnormality.
I think that when I was taught as a medical student, the auscultation findings in the chest were over-emphasised.  The reality is that these can be misleading.

First of all, the presence of focal findings in the chest are common even in the absence of LRTI.

  • The infant or child with URTI will often have crepitations that can be hear in one or more places in the chest.  These may be transmitted sounds or due to secretions.  Breath sounds will be normal throughout.  In the absence of abnormal breathing, these crackles are not good evidence for LRTI.  Often, these noises go away or move around if re-examined, especially after a cough.
  • The infant or child with a wheeze may have crepitations and variation in the loudness of breath sounds in different parts of their chest.  Bacterial LRTI does not usually cause wheeze but wheezy problems often lead to focal findings.  The clue that the problem is not a LRTI is that the child is systemically well.  The basic rule is this: if a child with a wheeze does not look ill enough to be admitted to hospital, they do not have a bacterial LRTI.  Bronchiolitis and viral induced wheeze are all the explanation needed for abnormal breathing.  If a child had one of these and a pneumonia, they would really be in difficulty. 
  • The child with viral induced wheeze may have no wheeze to further complicate things.  Consider a trial of beta-agonist inhalers in well child with respiratory distress, especially if there is a past history of wheeze. 
Secondly, the absence of focal findings in the chest is a relatively common scenario in the child with LRTI.
  • Auscultation and percussion in infants and small children is difficult.  Chests are small and there is always the possibility that the area of abnormality will be missed.  The child with cough, fever and abnormal breathing should be presumed to have a LRTI unless proved otherwise.
  • Not all LRTIs even produce focal signs.  Sometimes a segment of a lobe is all that is infected (known radiologically as a round pneumonia) and it is quite common in such cases for the only clues to be the combination of unwellness and respiratory abnormality.

Nor should we rely on chest X-ray (CXR) to make the decision for us.  The sensitivity and specificity of CXR as a way to diagnose pneumonia in children is too poor to justify using radiation when the diagnosis should be made clinically.   The BTS guidelines for community acquired pneumonia in children and the Clinical Practice Guidelines by the Pediatric Infectious Diseases Society and the Infectious Diseases Society of America both recommend that CXR and blood tests are routinely avoided. (1,2)

There are no absolute rules.  This is paediatrics so there are special circumstances.

  • Small infants and babies should be considered to have a higher probability of serious bacterial infection whenever they present.  However that should not mean a liberal use of oral antibiotics in a community setting.  If you are treating them differently because they have that higher risk of serious infections, they are also high risk for other reasons and should usually be referred if LRTI is suspected.
  • Children with complex medical problems may not demonstrate abnormal breathing or unwellness in the way that normal children do.
  • Children with chronic LRTI may be less unwell and have little in the way of respiratory abnormality.  Parents will often seem less anxious if the problem is developing more gradually.  Daily cough for several weeks should be taken seriously.  It is not unreasonable to try a course of broad spectrum oral antibiotics but be aware that this may not be the end of the problem.  Underlying causes including foreign objects, bronciectasis and simply unresolved LRTI may need to be ruled out in which case referral will be necessary.

Bringing all of these things together shows that there are two key features.  The first of these is abnormal breathing in the context of an unwell child with cough.  The presence of abnormal breathing almost immediately makes it overwhemingly likely that the problem is LRTI, bronchiolitis or viral wheeze.  The second feature is wheeze, which largely rules out LRTI.  It's almost that simple.  Almost...
For more on how to tell the difference between bronchiolitis and viral induced wheeze, read this post: "Why Do Different Children Wheeze Differently? - Simple, but first you have to understand all of paediatrics"

It is important to remember that LRTI is usually preceded by URTI.  Safety-netting advice is key.  Here's an example of the kind of thing that I tell parents: (3)
Ruling in and ruling out is a dynamic process.  Involving the parents is an important part of that.

Edward Snelson
Not a member of the ruling class

Disclaimer: Knowing whether you approach the problem from primarily a rule in or rule out approach is a bit like knowing whether you are coming or going, neither of which I am usually sure of.

  1. Guidelines for the management of community acquired pneumonia in children: update 2011 British Thoracic Society Community Acquired Pneumonia in Children Guideline Group
  2. Bradley J et al, The Management of Community-Acquired Pneumonia in Infants and Children Older Than 3 Months of Age: Clinical Practice Guidelines by the Pediatric Infectious Diseases Society and the Infectious Diseases Society of America, Clinical Infectious Diseases, Volume 53, Issue 7, 1 October 2011, Pages e25–e76,
  3. The Essential Clinical Handbook of Common Paediatric Cases, Edward Snelson