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Fever in Infants

Sixty-five percent of all children between the ages of birth and two-years-of-age are brought to medical attention for some type of febrile episode. And 75% of these visits are for temperatures greater than or equal to 39 degrees. We have this fear that when the temperature gets up that high that we may be dealing with a significant bacterial infection. In 14% of these kids thereís no definable source for the fever and thatís the problem. So the child that you donít have identifiable sources that you need to worry about, because that child could be either bacteremic. Could have meningitis or could have a bone or joint infection.

First of all, I want to define fever. There is a lot of confusion about what really is a fever in a child. Remember that children are smaller, like little birds and little cats and little dogs, they tend to have higher metabolic rates and because of that their core temperatures are higher than that of an adult. So for a child, a rectal temperature of greater than or equal to 38C degrees, or 100.4F degrees.

A few caveats. Remember that fever documented at home by a reliable adult should be treated the same way you would treat a fever reported to you by a nurse or a colleague. This is primarily for the house officers that I mention this. But you all well know this and we need to respect these readings by well or reasonable adults at home. Always ask about recent immunizations.

Serious bacterial infections can present with normal or subnormal temperatures. Keep that in mind. So an absence of a fever does not rule out a serious bacterial illness in a child. So donít be lulled into a false sense of security. An issue that we are not seeing right now, this time of year, is over-bundling. One of the problems is what do you do with a child who shows up in your office or in your clinic or in the emergency room, just totally bundled up.

Lastly, this issue. That the response to antipyretics does not predict the presence of bacteremia. Iím a dinosaur. Iíve practicing for a while and when I was a resident one of the things that our attendings liked to do, and the ER attendings liked to do, was give these kids a dose of Tylenol and see - aspirin.

Why do we worry about this? Well, this is the prevalence of serious bacterial infections in infants less than or equal to 3 months of age who come in with fevers of 39C degrees or greater. We are defining serious bacterial infections as these: meningitis, sepsis, bone and joint infections, urinary tract infections, pneumonia.

The players for kids less than 60 days of age are clearly different than the players of kids greater than 60 days of age. In this group, in the less than 60 days of age group, we are talking about group B beta streptococcus, E. coli, Listeria monocytogenes occasionally, staphylococcus, streptococcus, staphylococcus species and primarily staphylococcus aureus. Streptococcus pneumoniae and Hemophilus influenzae are starting to be seen more frequently. Weíve actually seen a few cases of kids whoíve had strep pneumoniae sepsis as a neonate. So neonatal sepsis due to strep pneumoniae. Probably has to do with inadequate antibodies transferred from the mother to the baby. The same thing with Hemophilus influenzae. We are not seeing Hemophilus influenzae type B disease anymore in kids.

In the older age group - that is, the 3 to 36 month of age group - the incidence of occult bacteremia, which is a frequent cause of fever of undetermined origin, seems to have decreased over time. McCarthy, which is one of the first studies out there in 1977, had an occult rate of bacteremia of about 7.1%. We are now somewhere around 3% to 5%. Most people are quoting numbers of 3% to 5%. So about 3 to 5 out of every 100 kids that show up with a temperature greater than 39C or greater or equal to 39C degrees is going to have occult bacteremia. The players in this have clearly, clearly changed. From the 70ís to the early 80ís.

So summarizing the data for kids 3 to 36 months of age, the prevalence is about 3% to 5%. It really doesnít matter where you are practicing medicine. You are going to see the same prevalence. The organism again is streptococcus pneumoniae. Thatís the major player we are seeing these days.

Why do we worry about occult bacteremia? Whatís the big deal here? So youíve got a few bacteria floating around in your blood stream, who cares? Again, this is a dead disease but it drives home the point as to why this bacteria was targeted for vaccine development very early on. If you look at Hemophilus influenzae B and you ask the question - hereís a kid who shows up in the emergency room, I draw a blood culture and I do nothing else but send him out the door.

Neisseria meningitidis is a little different. In a lot of patients out there - maybe 12 in one study - eight of these actually received antibiotics believe it or not and they still had this outcome. So persistence of bacteremia in one-quarter of those patients, meningitis in another quarter and in 17% they were dead on arrival because of, as you know, the progression of this disease. So this is not a good one to have floating around for a long period of time.

Can you tell these kids apart by looking at a clinical scoring scale? Again, it depends on what clinical scoring scale you are using but in general the vast majority of them fail to identify correctly the vast majority of kids who are bacteremic or non-bacteremic. Hereís just one of multiple studies, and Iíll quickly summarize it. This is 688 children between the ages of 3 and 24 months. Temperature was greater than or equal to 39.5C, so these kids were highly febrile.