Myths and Facts: Fever in children

In the latest in our series exploring some misconceptions about conditions seen in general practice, GP and paediatrics specialist Dr David Capehorn dispels some common myths regarding fever in children – and explains some less well-known facts.

Myths

Myth 1: High fever is dangerous and indicates a serious underlying illness

Many people believe that fever itself is dangerous and must be reduced immediately, when it is really a natural physiological response that helps the body combat infection.

NICE guidance does recommend fever is considered as part of risk assessment in young infants (specifically, a temperature of 38°C or higher in children younger than 3 months is considered high risk for serious illness, while a temperature of 39°C or higher in those aged 3-6 months is intermediate risk).

Other than in these situations, it is a misconception that the severity of an illness correlates directly with the height of a fever.

Viral illnesses can cause high fevers, while bacterial infections may result in little or no fever. Some children with sepsis may present with normothermia or hypothermia instead of fever, especially neonates and young infants. The hypothalamic thermoregulatory mechanisms are not fully developed, and immune responses are immature. Hypothermia in sepsis is associated with a poorer prognosis compared to sepsis with fever. Additionally, certain bacterial strains that produce toxins can alter thermoregulation, leading to an absence of fever. Therefore, the absence of fever in a child suspected of having sepsis should prompt careful evaluation and consideration of other signs of systemic infection, such as tachycardia, altered mental status, and decreased peripheral perfusion. It is crucial not to place excessive reliance on the presence or absence of fever when assessing a sick child.

There is also a widespread belief among parents that high fever can lead to brain damage in children. However, brain damage from fever typically only occurs at extremely high temperatures (above 42°C), which are rare without external heat sources. The body’s hypothalamic set point effectively prevents fever from reaching harmful levels during typical febrile illnesses.

These misconceptions can lead to unnecessary anxiety and premature medical interventions.

In summary, fever is primarily a beneficial response that indicates the immune system is actively fighting an infection and explaining this to parents can help to reduce anxieties.

Myth 2. Failure of fever to reduce with antipyretics indicates serious infection

Another common misconception among parents, and some clinicians, is that fever in children requires constant monitoring and frequent administration of antipyretics. Continuous monitoring of fever can lead to unnecessary anxiety for caregivers, without significantly improving health outcomes. The goal of antipyretic therapy is to enhance the child’s comfort rather than to return body temperature to normal.

There is no significant difference in health outcomes between febrile children treated with antipyretics and those who do not receive such treatment, provided the child remains comfortable. Fever reduction is not a reliable indicator of whether an infection is viral or bacterial and failure to reduce fever with antipyretics is not predictive of a more severe underlying condition.

Parents should be reassured that it is perfectly acceptable to allow mild fevers to run their course if the child is hydrated, comfortable, and exhibiting normal behavior. Again, it can be helpful in this situation to explain that ‘fever itself is not harmful; it is a sign that the body is actively fighting an infection’.

This balanced approach can help reduce anxiety and promote a more rational understanding of fever management in children.

Myth 3. The higher the fever, the higher the risk of febrile seizure

Febrile convulsions occur in otherwise neurologically normal children and are typically triggered by infections outside the central nervous system (CNS). (This does not include seizures resulting from CNS infections, such as meningitis or encephalitis.) There is no universal agreement regarding the specific temperature at which a seizure is diagnosed as a febrile seizure; some consensus guidelines indicate that an axillary temperature of >37.8°C indicates febrile seizure, others suggest a threshold of ≥38°C.

Interestingly, fever may not always be present before a seizure begins – it can sometimes develop after the seizure has occurred. Only about 4% of children will experience a seizure in conjunction with fever, and importantly the height of the fever is not a reliable predictor of seizure.

The age-related susceptibility to febrile seizures stems from developmental factors within the central nervous system, particularly the maturation of inhibitory pathways in the brain. Children aged 6 months to 6 years have a developing nervous system that may predispose them to seizures in response to fever. Consequently, most febrile seizures occur before a child reaches the age of 3, with approximately 60% of these cases happening in boys.

Febrile seizures may be more likely to be triggered by a rapid rise in temperature rather than the peak temperature itself. The speed at which fever develops can influence the excitability of the brain, making it more prone to seizure activity in vulnerable children.

However, the situation is more complex – recent research has identified specific genetic mutations that are associated with an increased risk of febrile seizures. Mutations in the SCN1A and SCN2A genes affect sodium channel function and have been linked to seizure susceptibility. Additionally, the FEB1, FEB2, and FEB3 loci have been associated with familial febrile seizures.

Febrile seizures are often triggered by viral infections such as influenza, adenovirus and human herpesvirus 6 (HHV-6). The body’s immunologic response to these infections – including the release of cytokines and inflammatory processes – may lower the seizure threshold in susceptible children, further complicating the understanding of febrile seizures.

In summary, while febrile seizures can be alarming for parents, it is crucial to understand that not all children are at risk. The interplay of developmental, genetic, and immunologic factors plays a significant role in determining a child’s susceptibility.

Myth 4. Recurrent febrile seizures are highly likely after a first febrile seizure

It is a myth that children are highly likely to experience recurrent febrile seizures following their first one. While there is a risk of recurrence, most children do not go on to have more than one febrile seizure. After a first febrile seizure, the risk of any recurrence is approximately 17%, while 9% of children experience two recurrences. Just under 6% experience three or more recurrences. Around 75% of recurrences occur within the first year following the initial febrile convulsion.

Certain factors can increase the likelihood of recurrence. Children who experience their first febrile seizure before 18 months of age are at a heightened risk, as are those with a strong family history of febrile seizures. Additionally, a shorter interval between febrile illnesses can further elevate the risk of recurrence.

Myth 5. Children who have febrile seizures are very likely to develop epilepsy

On the contrary, most children who have febrile seizures will not develop any form of epilepsy. In most cases, simple febrile seizures are entirely benign, with the overall risk of developing epilepsy being low. A simple febrile seizure lasts less than 15 minutes, is generalised in nature (not focal) and there is full recovery in an hour, without recurrence within 24 hours.

The general population baseline risk of epilepsy is 1%. When considering all febrile seizures, the risk ranges from 2-7%, which is still low in absolute terms. However, for those who have had a simple febrile seizure, the overall risk of developing epilepsy is estimated at approximately 2-3%.

Complex febrile seizures, characterized by focal onset, a duration exceeding 15 minutes, or recurrence within a 24-hour period, are associated with a higher risk of both recurrence and progression to epilepsy. The distinction between simple and complex febrile seizures is therefore crucial in assessing long-term outcomes. A family history of epilepsy significantly elevates the risk, with research on genes like SCN1a being important. Children with multiple recurrent febrile seizures are at a slightly increased risk of developing epilepsy compared to those who have experienced only a single febrile seizure episode. Furthermore, the age at which febrile seizures occur plays a role: children who experience febrile seizures after the age of three years face a higher likelihood of developing epilepsy.

In summary, while the risk of developing epilepsy after febrile seizures is indeed elevated compared to the general population, it remains low in most cases, particularly for simple febrile seizures.

Facts

Fact 1. The definition of fever can vary

Normal body temperature for children can vary slightly but generally hovers around 36.5°C to 37.5°C (97.7°F to 99.5°F). Several factors can influence this measurement, including the time of day, the child’s activity level and the method used for measurement.

Body temperature is not static; it fluctuates throughout the day due to the body’s natural circadian rhythms. Typically, temperatures peak in the late afternoon and early evening, which means that a reading of 37.5°C may not necessarily indicate a fever, particularly in the context of daily variations.

A typical low-grade fever at any age in childhood is usually defined as a temperature of 38°C (100.4°F) or above. This threshold is significant as it indicates an elevated response that usually signals the presence of an infection or other inflammatory process in the body. Special caution is needed when interpreting fever in young infants (under 3 months) due to their immature immune response and any fever at that age requires careful attention.

Understanding these nuances helps differentiate between normal variations in body temperature and genuine febrile responses.

Fact 2. Fever is responsible for 20-30% of paediatric visits to emergency departments

This high percentage attendance underscores the significance of fever as a clinical symptom, as well as the anxiety it can cause for caregivers.

This is particularly the case in young children, in whom febrile illnesses also frequently prompt visits to the GP.  It is estimated that around 20-40% of GP consultations for young children under 5 years involve fever or fever-related concerns. There is an ongoing debate about whether GPs are becoming deskilled in managing fever-related illnesses in children, due to changes in primary care structures. The increasing use of alternative workforce options – such as paramedics, nurse practitioners, and physician associates – to triage and manage these cases may be contributing to concerns about the erosion of GPs’ experience and confidence in these areas. However, while this theory is gaining attention, there is limited hard evidence to support the claim that GPs are being significantly deskilled as a result.

Another area of concern is whether the delegation of cases traditionally managed by GPs has led to a rise in hospital presentations, particularly for children with fever-related illnesses. Some suggest that alternative workforce professionals may be more risk-averse or less experienced in managing paediatric fever cases, potentially resulting in more referrals to emergency departments. However, the data to definitively link these workforce shifts with an increase in hospital presentations remains inconclusive.

Fact 3. Fever is a protective response that enhances immune function

Fever serves as an important protective mechanism. The rise in temperature creates a less favourable environment for human pathogens, which thrive at normal body temperatures.

Moderate fevers over 38°C are particularly beneficial as they stimulate the immune system in several ways. The fever ramps up the body’s immune response by improving the mobility of leukocytes, enhancing the process of phagocytosis, and boosting the production of acute-phase reactants.

As such, fever itself should be seen as part of the strategic immune defense mechanism. Conveying the message that moderate fever enhances the effectiveness of the immune system responses can help reduce unnecessary anxiety.

Fact 4. The appropriate method of temperature measurement depends on age

Using age-appropriate methods of temperature measurement ensures reliable assessments and appropriate clinical decisions.

Rectal thermometers provide the most reliable temperature readings due to their core body temperature accuracy, but they are not recommended for routine use in infants and children under 5 years of age due to discomfort, invasiveness, and the risk of injury or infection.

The advice, especially in younger children (as in the NICE guidance below) is to measure temperature using an electronic or chemical dot thermometer in the axilla. This method tends to slightly underestimate core body temperature and can be influenced by environmental factors.

Tympanic methods are suitable for children aged 4 weeks and older. These thermometers are popular due to their speed and ease of use. However, accuracy depends on proper technique, including correct positioning and ensuring the ear canal is free of obstructions like earwax. They may be less accurate in younger age groups and NICE does not recommend their use in babies under 4 weeks of age. As children grow, tympanic or oral methods can become more reliable, but each has limitations based on the child’s ability to cooperate and anatomical differences. Oral thermometers, typically digital, are more commonly used in older children and adults and can provide reliable readings if used correctly. However, factors such as recent eating, drinking, or mouth breathing can affect accuracy, and proper placement under the tongue with the mouth closed is crucial. Forehead chemical thermometers are not routinely advised by NICE as they are less accurate.

In summary:

• Under 4 weeks of age: use electronic thermometers in the axilla.
• Over 4 weeks of age: use axillary thermometry as above or infrared tympanic thermometers.

Fact 5. Over-reliance on decision tools can lead to over-investigation

Clinical decision-making tools have been developed to assist clinicians in determining which febrile children might have a serious illness. However, all these tools have limitations – they may not have been validated in independent datasets, may lack consistent performance, have insufficient accuracy, or only apply to specific age groups.

NICE developed the Traffic Light System to help healthcare professionals assess the risk of serious illness in children under 5 who present with fever. Designed for use in a variety of clinical settings, including general practice, the system categorises symptoms and clinical signs into three colour-coded risk levels – red, amber, and green – each indicating the urgency and type of care required. The goal is to standardize assessments and improve decision-making.

However, a 2022 study evaluated the accuracy of this system in 6,703 children and found it was less reliable than expected. The system was more effective at identifying children at low risk of serious illness (green category) than those at high risk (red category). Many children classified in the red and amber categories did not have serious illnesses, highlighting a potential issue of over-triage. This could lead to unnecessary anxiety for parents and possibly unwarranted healthcare utilisation. Conversely, the green category effectively identified children who were unlikely to have serious conditions, supporting its value in reassuring clinicians and caregivers.

Clinical judgement remains essential, particularly when the system indicates higher risk levels. This outcome is somewhat expected. Fever can alter a child’s mental status, causing irritability, lethargy, or reduced responsiveness, which might be mistaken for more severe neurological issues. These behavioural changes can complicate the assessment of the child’s level of distress or discomfort. Fever can also exacerbate symptoms like tachypnoea and tachycardia, leading to an overestimation of the severity of respiratory or cardiac conditions during a physical examination. This could result in unnecessary investigations or treatments based on a misinterpretation of fever-related signs.

Dr David Capehorn is a GPwSI in paediatrics, founder and former clinical director of the Paediatric GPSI Primary Care Paediatric Service in Bristol, and honorary associate specialist at Bristol Children’s Hospital Emergency Department.

The author is grateful to the following for guidance in the preparation of this article: Dr Matthew Capehorn, Clifton Medical Centre in Rotherham; and Faith Tinley, Training and development Sister at the Vale Hospital, Dursley