Juniper is a 3yr old girl brought in with her mother, with a 48hr history of fever. Her mum is particularly concerned because her fever was up to 39.8°C, didn’t come down with paracetamol and she describes an episode which sounds like a rigor. On examination, she has a temperature of 39.3°C, a runny nose and bright red tonsils, and looks otherwise well. You go to discharge her, but your colleague asks if you should wait to see if her temperature comes down with ibuprofen before sending her home?

 

Introduction

Febrile illnesses are the most common cause of presentation to acute paediatric medical services. This means that fever is the most common presenting symptom seen by paediatricians, and it is clearly a huge cause of concern for parents. Despite this fact, it is clear that in day-to-day practice that there is a widespread misunderstanding about fever, its purpose, and its clinical interpretation.

Well, no longer! Once you have finished reading, you will be a master of all things related to fevers in children. We will start with some basic understanding of the processes surrounding fever, and finish off with some mega myth-busting!

What is fever?

Fever is an elevated core body temperature, as part of a physiological response to infection regulated by the hypothalamus. This is crucial to understand – your body is in control of your temperature. This is not something an infection is doing to your body; it is something your body is doing to the infection. This is different from pathological hyperthermia, where your temperature is elevated by either hypothalamic dysfunction or external heat. These are extremely rare.

Note: there are other, non-infectious causes of fever, such as cancer, Kawasakis, and autoinflammatory conditions, but these are rare in comparison to infectious fever and are covered elsewhere.

 

What temperature counts as a fever?

At what threshold do we say a child has an elevated body temperature? This is more controversial than one might think, as actually the data from which we derive “normal” body temperature is extremely poor. The most common cut off for defining a fever is 38°C – but it is important to remember that there is nothing magic about 38°C compared to 37.9°C, and temperature is better taken in context or a trend, if possible.

How do we get fevers?

The process of developing fever is extremely complex, and our understanding is still developing. At present, our best explanation is that the process is triggered by the presence of chemicals referred to as pyrogens. Pyrogens can either be exogenous (such as parts of the microbe itself, like the lipopolysaccharide on the outside of bacteria), or endogenous, such as cytokines like IL1, TNF, Prostaglandin E2 and importantly IL6, which are released by immune cells when they detect an invader. These pyrogens act to increase body temperature peripherally, but importantly also trigger receptors in the preoptic nucleus in the brain. This releases PGE2 into the hypothalamus, which then sets a new target temperature. This target is met by many facets designed to increase heat, including:

• Release of noradrenaline by the sympathetic nervous system, increasing thermogenesis in brown adipose tissue and causing peripheral vasoconstriction and piloerection (reducing heat loss)
• Acetylcholine release stimulating muscle myocytes to induce shivering
• “Feeling cold”, inducing heat-seeking behaviours (warm clothes and blankets)

It is important to remember that the body is trying to get hotter. If you intervene with non-medicinal efforts to cool it down, it will work even harder to try to heat up.

Why do we get fevers?

The process of having a fever has been conserved across species from lizards to mammals, and even plants! This is because it is a beneficial response to an infection. The mechanisms by which a fever helps protect you from infection include:

1. Higher temperatures inhibiting growth/replication of pathogens
2. Higher temperatures promoting the immune response to infection

It is also worth noting that bacteria are killed more easily by antibiotics at higher temperatures, so there is also a potential third mechanism.

 

Summary

Fever is beneficial. When a pathogen causes infection, pyrogens stimulate the hypothalamus to increase the body temperature through several mechanisms, and this increased temperature helps inhibit the growth of the pathogen AND stimulates the immune system to fight it.

That was a lot of science. Don’t worry – it’s time to get clinical! All this science stuff is lovely, but what does this mean for our patients?

Clinical significance of fever

As we have ascertained, fever is beneficial. For this reason, when a child presents with fever, the fever itself is actually of no concern. What we are interested in is the reason for the fever. Is this fever the result of a benign, self-limiting, childhood infection – or is it associated with a serious bacterial infection? Trying to determine this is enough for its own blog article (the most important thing is the end of the bed assessment – see Andy Tagg’s excellent breakdown of the paediatric assessment triangle).

Ignore the fever itself – what’s important is ascertaining its cause.

Now, let’s get on and bust some myths that persist surrounding fever in children!

 

Myth 1 – Higher temperature indicates a serious infection

This is one of the most common concerns amongst parents. The particular height of temperature may be what prompts them to come to hospital, or even what prompts the health care provider to initiate more aggressive management or investigations.

The truth is that the relationship between the height of temperature and risk of serious illness is at best complicated, and at worst a dangerous distraction. There is a very poor correlation, with such woeful sensitivity and specificity that it will both grossly over and under-call serious infections (either if the high temperature is used to rule in, or lower temperature to rule out). The caveat to this is in younger infants (particularly under 60 or 90 days), who have a higher baseline risk of serious infections (and more to the point – once they spike a temperature will be managed aggressively regardless of how high it was). Some studies have shown an extremely weak association in older children, but not enough for it to have any meaningful influence on our management. A fever is a fever – higher temperatures should not be managed any differently than lower ones.

 

Myth 2 – Temperature not relieved by antipyretics indicates a serious infection

Another common misconception also linked to the myth above. Some fevers respond well to antipyretics, and some do not. We do not understand why this is the case, however, studies have not demonstrated that failure to respond to antipyretics is a useful indicator of a more serious infection. It is not very pleasant for the child to remain hot, but it does not mean they are at any higher risk. A child whose temperature does not respond to antipyretics should not be treated any differently to one that does.

Myth 3 – Rigors indicated a serious infection

This has been covered in-depth in a separate blog post – but to summarise; there is extremely weak evidence that rigors are associated with an increased risk of bacterial infection in children, which is irrelevant when factors that are more important are taken into account. There is also evidence of no increased risk. The presence or absence of rigors should not be a deciding factor in the management of febrile children.

Myth 4 – You must wait for a fever to come down before discharge

This may seem common practice for many of you working in acute paediatrics. If a child is febrile on arrival, people often want to wait to see the temperature come down before allowing them to be discharged (this should be differentiated from seeing observations normalize in the absence of fever – which is a more understandable if still slightly questionable practice). As we have seen, a fever merely indicates the presence of an infection. If you have ascertained the cause of the fever, or at least ruled out any red flags for serious causes, the ongoing presence or absence of a fever means nothing for the child. If it comes down before discharge, it will probably just go up again once they are home! There is no need to make them wait around for hours for no reason.

Myth 5 – Fever should be treated with antipyretics

We have established that fever is beneficial. Therefore, there is essentially no reason to treat a fever in and of itself. It will not cause harm, and it is probably helping. Some children tolerate having higher temperatures extremely well, so if they are playing happily or do not seem terribly bothered about their temperature of 39°C then you leave them well alone.

Treat the child, not the fever.

Myth 6 – Fever should not be treated with antipyretics

There is an opposing school of thought, which says that since fevers are beneficial, we should not treat them at all. Given how absolutely dreadful it can feel to have a fever (which many of us adults should be able to vouch for), many of us give medicines to try to bring the temperature down and make the child more comfortable. This is the right thing to do. Despite the potential benefits having a fever confers, there is no evidence of any clinically meaningful harms to treating temperatures in unwell children, or even in adults in ICU. If the child is distressed by the temperature, they should have antipyretics to make them feel more comfortable.

Summary

• Fever helps your body to fight infection and is not dangerous (no matter how high)
• The fever itself is not important. The cause of the fever is what matters
• There is little to no evidence that higher temperatures, temperatures that don’t respond to antipyretics, or rigors indicate an increased risk of serious infection
• Persisting fever on its own is not a reason to postpone discharge
• Only treat fevers if they are causing distress. Treat the child, not the fever

 

Postscript: Febrile convulsions

When I posted my initial thread on twitter about fevers, there were many comments asking why I didn’t address febrile convulsions. This was mainly because these are worth a post to themselves (which they have here). In brief, febrile convulsions are extremely distressing for parents to observe, but they are common and they are very benign. We do not advise treating fevers to prevent febrile convulsions, and until recently, this was because there was no evidence that they had any effect in preventing them. A recent study from Japan did demonstrate a decrease in recurrence of febrile convulsions in children who had already had one if given regular PR paracetamol, however, there are major caveats to this study discussed in depth here.

 

For the more visual oriented, the talented Emma Buxton has created an infographic of the key reminders from this blog post: