Fever and Bacteria and Children

Expert / 15 December, 2018 / Dr Clare Thompson

What to Do When Your Child Has a Very High Fever – All Your Fears Addressed Here

My son had a very high temperature last week, it spiked in the middle of the night and thank goodness I checked on him before I went to bed. He was a little under the weather at 7pm, but he had no temperature. Fast forward to 11pm and he was absolutely boiling, at a 103f. This is something I always worry about, and often forget to ask the doctor, usually finding I can manage to keep a temperature down using Calpol and nurofen. Our resident expert and GP Dr Clare Thompson explains in this in depth guide the causes of temperatures, the differences between a bacteria infection and a virus, and what parents can do at home to help their child. 

The most common consultation I have with mothers and their young children is the presentation of a fever and how to manage it at home. A fever can be absolutely terrifying for a new mum and even experienced parents will face a few sleepless nights at the mercy of their child’s thermometer.

A common misconception is that a fever is always bad and a child should be given Calpol and ibuprofen every time they feel warm to the touch. Equally, when a child is becoming seriously unwell an UNCONTROLLED fever can be a warning sign of deterioration. This is confusing for parents and can leave you feeling uncertain of when to treat a fever. We always need to consider what’s causing the fever and make a judgement on whether to see a Doctor or manage the fever at home in the first instance, since most infections are actually viral.

The best way to measure your child’s fever is with a tympanic thermometer which is inserted into the ear. The instruments used in your Doctor’s office should be calibrated every few months to ensure that they are accurate as well.

The average child will have between 8-10 illnesses in a winter period, maybe even more if they have just started a new nursery or school due to exposure to a new set of germs. The majority of these will be viral and will settle with conservative management of keeping the child comfortable. Part of keeping a child comfortable is to reduce pain and keep them well hydrated.

If your child is under 3 months of age and has a fever then it is especially important that you see a Doctor quickly for urgent same-day assessment. These little ones have far less reserve and Calpol and nurofen are not licensed for use in very young babies.

Viruses and Bacteria and How They Affect the Body


Bacteria are single-celled micro-organisms with a cell wall and machinery inside it for replication which are considered to be ‘alive’ and living. They contain their own DNA to replicate and do not rely on the host to do so. They can be considered as beneficial (e.g./ good bacteria in the gut) or harmful (e.g./ bad bacteria attacking the tonsils) for the health of humans coming into contact with them. Bacteria are more likely to also attack cells directly and cause damage to the tissue itself (e.g./ bacterial throat infections like strep).


A virus is a micro-organism which is smaller than a bacteria and cannot grow or reproduce alone. It is essentially a piece of code (a nucleic acid molecule in a protein coat) which invades living cells and uses their chemical machinery to keep itself alive and to replicate itself. They are considered to be ‘non-living’. Viruses are more likely to activate immune pathways than attack body tissues directly.

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How do viruses and bacteria cause a fever?

The hypothalamus is a small area of the brain which is essentially the body’s thermostat and is responsible for regulating core body temperature. Body temperature is determined by the balance between heat production in muscle tissue and internal organs and heat loss to the external environment.

When your body temperature rises because of an infection, it is called a fever. Fever results when a virus or bacteria raises the hypothalamic set point and triggers narrowing of blood vessels to the outside of the body to reduce heat loss and also induces shivering. Fevers are caused by chemicals called ‘Pyrogens’ flowing in the bloodstream. These pyrogens then bind to receptors in the hypothalamus in the brain and the body temperature rises.

One common pyrogen is called Interleukin -1 (IL-1) which is produced by white blood cells (fighter cells) after they come into contact with foreign material. IL-1 also signals and recruits other fighter cells in the immune system to fight the bacteria and viruses. One thought is that the purpose of a fever is to raise the body’s temperature enough to kill off foreign material – so in essence your body is working to help you.

Consequences of Fever

Although many people worry that fever itself can cause harm, the modest core temperature elevations (38-40c) caused by most acute illnesses are well tolerated by the body and may even be protective. However, extreme temperature elevation (>40c) may be damaging and trigger an inflammatory process which results in protein destruction. High fever in children can cause febrile convulsions (a seizure as the body short- circuits due to a very high temperature). A fever will also often cause temporary confusion and delirium. High fever in the elderly can worsen mental status, especially in those patients with Dementia.

The Immune System

The immune system is a complex network responsible for protecting the body against foreign substances including viruses and bacteria.

There are several lines of defence:

A/ Skin and airways

When foreign material is first encountered the nasal passages and airways are the first line of defence. Often a patient will suffer with inflammatory changes causing increased mucus secretion from the nasal passages and coughing. Rashes may also occur as a response of the skin which is the body’s largest organ.

B/ The Tonsils and Lymph nodes

When foreign material breaks through the skin and nasal passages it enters the blood stream and will trigger inflammatory pathways to activate cells in the immune system to defend itself and results in a sore throat, swollen tonsils and swollen lymph nodes (glands). Coughing is due to an inflammatory response activated in the airways and this causes broncho-constriction sometimes experienced as a tight chest and wheezing.

When to treat a fever?

Ultimately if your child has a low grade fever and is well with it then it is acceptable to watch and wait for a while. Often the body will counter-attack the offending virus or bacteria in the initial stages and the fever will settle within the first 24-48 hours. If your child has good energy levels, is drinking plenty of fluids and is not in pain then it is safe to watch and wait initially.

If your child has a low grade fever and is in discomfort or has one of the following:

  • poor fluid intake
  • apetite reduced
  • specific pain (e.g./ear or throat)
  • poor energy levels
  • very unsettled and miserable

then it would be sensible to start giving some Calpol or nurofen to keep your child comfortable and try to top up their fluid intake to maintain their hydration levels. The Doctor will usually advise aiming for a temperature of < 37.5c as a general rule.

The reason the information on the box of Calpol advises parents not to give it for more than 3 days is that you should really be consulting a Doctor after 48 hours to have your child examined properly to ensure that they are not suffering from an illness that requires more definitive treatment and /or investigation.

A Doctor will be able to assess your child and make a sensible decision about whether there are clinical signs when the child is examined (e.g./ noises on the chest, redness to ear drum, pus covered tonsils) that require an antibiotic to be started or not. If an antibiotic is initiated then the medication will often take a good 48 hours to take full effect and until that time parents are advised to use regular Calpol or ibuprofen to try to keep the child’s temperature < 37.5c for comfort.

A note on Febrile Convulsions

Febrile convulsions affect up to 10% of children aged 6 months to 6 years of age. Parents should be reassured that the vast majority of children will grow out of them with no future problems. There is a higher risk of a further febrile convulsion in children who have had one in the past but most children will recover quickly and get back to normal. The important thing to remember is that there is nothing that you can do to completely stop your child from having a febrile convulsion and that sometimes fitting can occur quite early on in the fever – in fact the fever may continue to rise even after the fit has occurred. Be careful with measures to bring yours child’s temperature down too quickly as sudden changes in temperature can do more harm than good and a fever is partly the body’s way of responding to an infection.

Other causes of fever

Another tip for parents is to remember that it is possible to have multiple infections at different sites of the body at the same time. So if your poorly child is being treated with antibiotics for one infection but continues to be in distress and have an uncontrolled fever then it is worth taking them back to the Doctor to be re-examined and having a urine sample checked. Children can have co-existing urine infections that may be driving the temperature symptoms which may be overlooked by the Doctor.

Calpol and Nurofen: The Great Debate

Ask any mother what is in her bathroom cabinet and most will have Calpol and Nurofen in there somewhere along with other life essentials such as plasters, antiseptic and lipbalm!

There is no great advantage to lowering a temperature just for the sake of lowering it. I would advocate that it is only sensible to start the Calpol and Nurofen if your child has BOTH a temperature and is in discomfort from it.

The parents I see fall into two camps: Calpol OR Nurofen. Put simply, some children respond better to one than the other.

I spoke to Dr John Fysh Consultant Paediatrician at The Portland Hospital and he concurs that most children will respond better to one medicine than the other. Using the medication that works best for lowering your own child’s fever would be sensible advice.

How do Calpol and Nurofen Work?

Calpol is a pretty trusty medicine that has been around for a very long time. Calpol preparations contain children’s doses of paracetamol and often have added sugars for taste (this is actually quite important as most kids will not want to take an unpalatable medicine when they are unwell). It is given for relieving mild to moderate pain and reducing a high temperature.

Calpol and Nurofen reduce pain by inhibiting Prostaglandins in the body which are responsible for controlling our pain thresholds. It also reduces fever by acting on the hypothalamus in the brain which controls core body temperature. It also acts to induce sweating and dilation of blood vessels at the outside of the body which subsequently lowers body temperature.

Nurofen is also an anti-inflammatory medication which switches off pathways of inflammation. Of the two medications Calpol is perhaps slightly safer, but some children definitely respond better to Nurofen preparations. Again, it’s best to use the medication that works best for lowering your own child’s fever.

Can I overdose my child?

Medication errors can tend to occur when there are multiple care givers involved. A good example is where a child is looked after in the daytime by a nanny and then parents are not handed over exactly how much calpol was given during the day and when.

It is unusual to see a child overdose on calpol or nurofen and even if a care giver accidentally gave a double dose once or twice, the doses on the medication box must be safe for use at home by a non- medical person. The risk would be where parents are giving high doses for several days rather than a short period of time. The reality is that much larger doses are used in a hospital setting under the watch of Doctors and Nurses.

As a rule of thumb try to stick to one agent (the one your child responds best to usually) and try not to give more than the recommended frequency.

Starve a Fever, Feed a Cold?

When a child has a fever they will lose lots of fluid via sweating and breathing which can quickly result in dehydration. Vomiting and diarrhoeal illnesses will also result in extra fluid losses and so it is essential that caregivers try to replace and rehydrate the child quickly. As long as the fluid replacement contains some sugar it is safe for a child not to eat for a short while.

Signs of dehydration:

  • Sunken fontanelles (the soft part of your babies skull – ask your doctor to show you how to feel this properly)
  • Dry mouth
  • Sunken eyes
  • Absence of tears when crying
  • Dry nappies and low energy
  • Cool hands and feet

The children most at risk of dehydration are those younger than 6 months, infants born with low birth weight, children who have vomited three times or more or those who have had six or more diarrhoeal stools in the past 24 hours and babies who have stopped breast or bottle feeding during the illness.

It can be tricky to assess your child’s hydration status and this is where an experienced Doctor should be consulted to examine your child and ask specific questions to make a diagnosis.

Other things you can do to protect your child this winter

In the wintertime the air is less humid and much drier. There is evidence that viruses and bacteria cross the mucous membranes of the nose and airways more easily in these conditions. One school of thought is to employ the use of a humidifier in your child’s bedroom to keep the air moist. Another tip is to use saline drops to keep the nasal passages moist. I often tell my adult patients to use nasal washes to try and cleanse the mucous membranes and reduce the risk of viruses and bacteria infecting them.

I would also suggest that nurseries, schools and Doctors Surgeries take the time to disinfect the children’s toys once a day to reduce the risk of transmitting germs to one another as these are key places children share bugs with one another via direct touch. Equally, frequent hand washing should be employed to the same effect where possible.

Take Home Messages:

  • Do NOT employ tepid sponging – it is ineffective at reducing the fever
  • Do NOT overdress or underdress a child with a fever
  • Do NOT give calpol and nurofen at the same time but consider using the alternative agent if the child doesn’t respond as well to the first drug
  • Do NOT give calpol and nurofen routinely if the sole purpose is just to lower the temperature
  • Do NOT give calpol and nurofen with the sole aim of preventing febrile convulsions – it will NOT prevent them
  • If a child has a low grade fever and is WELL with it then there is a strong argument NOT to give calpol and nurofen
  • If a child has a low grade fever and is in DISCOMFORT from it then it is sensible to start calpol or nurofen
  • Remember to keep your child well hydrated as a fever will cause the child to sweat and lose fluid

By Dr E Clare Thompson, The Courtfield Private Practice, South Kensington.

The Courtfield Private Practice’s head partner is Dr Tim Ladbrooke, the GP in Tatler’s Best Doctor Guide. The practice is expanding and and concentrating its focus on mothers and children. 

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