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Fever

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What is a fever?

Many people think that a "fever" is any temperature above 98.6 degrees Fahrenheit (equal to 37.0 degrees Celsius).

However, our temperatures change constantly during a normal day. We tend to be cooler when we're asleep (especially at night), and warmer when we're awake and active. The "thermostat" in our brain, which controls blood flow to the skin (more when we're warm, less when we're cool), sweating (also more when we're warm and less when we're cool) and shivering (we shiver when we're too cool), tries most of the time to keep our temperatures between 97.5 and 99.5, and usually does a pretty good job of it.

When we are sick, whether from an infection or from other causes, our thermostats turn the temperature up. This actually helps when you have an infection: a fever helps your body get rid of bacteria and viruses, many of which will grow well at normal body temperatures but not at the higher temperature of a fever. Thus it's not always a good idea to try and bring down a fever all the way.

Of course, fevers do make you uncomfortable. More important, high temperatures can cause problems, including seizures in some people (although seizures don't usually happen unless your temperature is 104-105 or higher). Unless your doctor tells you to, don't try to bring your child's temperature all the way down to 98.6, because that may actually prolong the illness by delaying your body's efforts to kill bacteria and viruses. We define "fever" as a temperature of 100.4 F or higher. Unless your doctor suggests it, you shouldn't give anything for fever unless your child's temperature is 100.4 or higher (and possibly not unless it's higher than 101). (As always, remember that not all doctors do things the same way; if your doctor gives you different advice, you should follow it -- after all, your doctor knows your child better than I can.)

How do I take a temperature?

How you take a temperature depends partly on how old your child is, and partly on the kind of thermometer you use.

Kinds of Thermometers

Glass Thermometers

The old-fashioned mercury-filled glass thermometer takes a long time to work. They are also illegal in many areas. Mercury is poisonous, and very hard to clean up if it's spilled. Some communities now offer free non-mercury thermometers to people who turn in their old mercury thermometers, so that they can collect the mercury and dispose of it safely. Also, mercury thermometers are made of glass, and broken glass is also hazardous. If you have a mercury thermometer, you should dispose of it -- promptly and properly (and not in the regular garbage!).

Electronic ("Digital") Thermometers

These come in many different shapes and sizes, but they all consist of a "probe" which produces an electric signal that depends on temperature and a display (usually in numbers) that shows you the temperature. They are almost all battery-operated (if you buy one, you should also get a spare battery or two), and very hard to break. They also register the temperature faster than glass thermometers, and beep when they have finished measuring the temperature. I recommend these thermometers especially for small children.

NOTE: The numbers and the decimal point on digital thermometers are very pretty. That does not mean that a digital thermometer is more accurate than a mercury thermometer, or than other kinds of thermometers. The inexpensive digital thermometers sold in drugstores can be less accurate than mercury thermometers, although the digital thermometers we use in our offices are usually more accurate (and harder to break, too). Don't assume that the digital thermometer will read a temperature accurately just because it's digital.

Ear Thermometers

These use electronic sensors to measure the temperature of the eardrum, which happens to be very close to the brain's thermostat. They are very fast, but have to be in the ear canal within sight of the eardrum, which makes them hard to use on small babies and children with curved canals. (Babies' ear canals are smaller and more twisted than in older children. It's actually not easy even for us to see a small baby's eardrums in the office or hospital. We use ear thermometers often in offices and emergency rooms because of their speed, but they may not be all that great at home, and I personally don't use ear thermometers to take a small baby's temeperature.

Temporal (Forehead) Thermometers

There are also thermometers that measure temperature of the forehead or temples; some of these are strips of liquid crystals that change colour with temperature, while other, newer thermometers use infrared scanning similar to that of the ear thermometers. These are easier to use, of course, but there are studies showing that temporal thermometers do not show true (high) core temperatures in someone with high temperature caused by heat stress -- which may make you miss rising body temperature in hot weather.

Where to take a temperature

Under the arm

This is the easiest place for a temperature, especially for small children. Place the probe right in the armpit, and hold your child's arm down so that the probe is surrounded by arm and armpit. NOTE: when you take the temperature under the arm, do not add 1 to the temperature you see on the thermometer. This "correction" doesn't work with everybody. (I have seen babies who had unnecessary spinal taps because parents mistakenly added 1 to what was on the thermometer.) Instead, tell your doctor

  1. what temperature the thermometer showed, and
  2. where you took the temperature.
This will give your doctor a much better idea of what your child's temperature actually is.

Orally

Place the probe under the tongue, and as far back under it to one side or the other as you can. (The farther back under the tongue you have the probe, the faster and more accurate the measurement.)

Rectally

Warning: do not take a rectal temperature on small babies unless your doctor asks you to. Putting a thermometer in the rectum may injure the baby.

First lubricate the probe with Vaseline. Then place the probe in the anus, so that the temperature-sensitive part of the probe is completely inside.

In the Ear

Follow the instructions that came with your thermometer (some models are different from others).

What should we do about the fever?

Infants

Babies less than 8 weeks old
WARNING:
If you are reading this because your baby has a fever (a temperature of 100.4 or higher), stop right now, get on the phone, and call your doctor. A fever in a baby this young is an EMERGENCY!

A baby less than 8 weeks old can have a fever for many of the same reasons that older kids and adults do, including viral colds and sometimes even stomach flu. The problem is that we cannot tell just by examining a baby whether the fever is caused by a virus or by a bacterial infection. At this age a baby doesn't have all the defenses against bacteria that older people have, and so they can end up with an overwhelming infection, or sepsis. To find out for sure whether a baby with a fever has or does not have a bacterial infection, we need to take samples (of blood and urine, and often of spinal fluid) and try to grow bacteria from them. This can take 2 days, but we have to start giving antibiotics right after taking the culture samples, or else if there is an infection we may not catch it in time. We probably give 95 children antibiotics for 2 days without having to for every 5 children who have infections, but the consequences of not giving antibiotics to the 5 children who need them are such that we take no chances with the other 95.

So, if your baby is less than 8 weeks old and has a temperature of 100.4 or higher, you need to call your doctor immediately. There may be circumstances (such as overbundling) where the high temperature does not mean there is something very wrong with your baby, but you should let your doctor help you sort it out. Many doctors want to see any baby under 3 months old with a fever: check with your doctor (when your baby is born) to see how s/he likes to handle a baby with a fever.

Babies over 2-3 months old
By this age babies are better at fighting off infections. However, as they get older they see more and different people and are more likely to pick up bugs from those people -- especially from their brothers and sisters. They are also likely to get fevers after immunizations: the whooping cough part of the DPT vaccine was particularly notorious for fevers, and I and many other pediatricians made a habit of giving babies Tylenol regularly for 2-3 days after a dose of DPT. (Any vaccine can cause a fever, but the whooping cough vaccine in DPT is the most likely to do so. The newer DTaP vaccine, which uses only parts of the pertussis (whooping cough) bacteria instead of the whole killed bacteria, is less likely to cause fever. Although many of us have continued to recommend Tylenol (or Motrin) after vaccination, there is more and more evidence that giving Tylenol after vaccination actually reduces the effectiveness of the vaccines. (See, for example, the Lancet, volume 374, pp 1339-1350, October 17, 2009.)

If your 2-month or older baby has a fever, Tylenol may be helpful if the temperature is high (over 101, even over 100 if they are uncomfortable). If you have any doubt that there might be something serious causing the fever, call your doctor.

Between 6 months and 3 years

Fevers in children at this age can be sorted out a bit more easily -- especially since they're usually caused by bugs picked up from others, often other children. (As a rough rule of thumb, if your child is in day-care or school, you can expect him or her to to pick up something every 2 or 3 weeks.) Although many of these fevers are caused by viruses, and therefore cannot be treated with antibiotics, some problems, such as ear infections, are caused by bacteria and can be treated with antibiotics if needed.

It's also possible for a child with a high fever to have a seizure because of the fever. "High" in this case usually means 104 or higher, although rare children (often those with underlying seizure disorders) may have seizures with lower temperatures. If your child has a temperature of 104 or higher, and you can't bring the temperature down at home, call your doctor. We can suggest ways to bring the temperature down, and we can help you decide whether someone needs to examine your child right away. If your child has a seizure, with or without a fever, and has never had a seizure before, call your doctor or EMS immediately. (If your child has had seizures before, your doctor, or a neurologist (a doctor who specialises in problems with the brain and the nervous system), should already have told you what to do about a seizure and may even have given you medicines that can help stop a seizure in an emergency.)

Older children and pre-teens

Fevers in this age group are not nearly as much of a problem as with younger children. This is because
  1. they are better at telling you if anything else is wrong,
  2. they have had a few viral infections already (As we get older, we tend to have fewer viral infections because we have become immune to all the viruses we had when we were younger), and
  3. they can help (by good handwashing, for example) to reduce their exposure to other people's bugs.
Often you can just treat a fever without any other symptoms at home, and your child will get over it fairly quickly. If there are other symptoms, or if the fever is high or hangs around for more than 2-3 days, talk to your doctor -- your child may need to be examined to see if there is a bacterial cause.

Treating a Fever

Remember to talk to your doctor before treating your child at home if you have doubts about what to do, or if your baby is 8 weeks old or younger. There is lots of evidence that giving medicines for fever does not really help children with fevers due to infections. (See, for example, Bulletin of the World Health Organisation, vol 81, pp 367-372, 2003.)

The most common treatment for fever is acetaminophen (Tylenol, Tempra, and many other brands). These come in several different forms, including drops, liquid, chewable and swallowable pills, and suppositories. Generally, if your child needs Tylenol, you can just give it according to the directions on the package. However, if you have any doubts about the proper dose of Tylenol, or any other medicine for your child, call your doctor and ask. I have not given specific doses here because I believe that information should come from your doctor and be tailored to your child.

Sometimes you may have trouble bringing your child's temperature down with Tylenol alone: if this happens, your doctor can suggest different doses for the Tylenol, or may suggest another medicine such as ibuprofen (Motrin).

Many of us have recommended a combination of Tylenol and Motrin, in alternating doses, on the theory that the two medicines in combination would reduce a patient's temperature faster and for a longer time than either one alone. This had not been proven in studies until recently; a study published in the Archives of Pediatrics and Adolescent Medicine (vol. 160, pages 197-202) in February, 2006 shows that alternating Tylenol and Motrin does keep temperature down better in infants and small children than does either Tylenol or Motrin by itself. However, the medical literature overall isn't firmly in favour of using both medications at the same time. As always, ask your doctor whether the two-medicine treatment is right for your child, and how much of each medicine to give.

Another old standby, which works quite well, is a lukewarm bath. The water must be lukewarm: if it's too cold, your child's body will reduce blood flow to the skin, and that may make his/her temperature go up rather than down. The proper temperature is whatever feels about the same as your skin does, and sponging your child with the water may work better than just putting him/her in the bath. (And never leave a child in the bath unattended!) It is also a good idea to give Tylenol or another anti-fever medicine before putting a child in the bath. Tylenol and other anti-fever medicines turn down the body's "thermostat" so that the body doesn't generate more heat while you are trying to take heat away with the bath. Therefore, the bath will work much better after Tylenol or another anti-fever medicine.

Never give a child (or anyone under 25 years old, for that matter) aspirin, unless your doctor tells you to. Aspirin in a child with certain viral illnesses (such as chickenpox and mononucleosis) can produce a very serious liver disease called Reye's syndrome which can in turn cause seizures. There are a couple of childhood diseases that need to be treated with aspirin, but they are relatively rare.


Many thanks to Erin Duchan, MD, for a very helpful discussion of the value (and lack thereof) of medication for treatment of fever in children.


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PLEASE NOTE: As with all of this Web site, I try to give general answers to common questions my patients and their parents ask me in my (real) office. If you have specific questions about your child you must ask your child's regular doctor. No doctor can give completely accurate advice about a particular child without knowing and examining that child. I will be happy to try and answer general questions about children's health, but unless your child is a regular patient of mine I cannot give you specific advice.



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Copyright © 1996, 1998, 1999, 2002, 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2013 Vinay N. Reddy. All rights reserved.
Written 08/16/96; last revised 09/12/13
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