Last month I discussed the best method of measuring fever in infants and children. Now I’ll discuss the mechanism of fever and a general approach to the management of the feverish child concentrating on the 0-36-month-old child, including certain red flags for the general practitioner.
Fever is the result of the body’s response to illness, generally an acute viral or bacterial infection. I won’t deal here with fever that’s chronic (present for longer than 3 weeks) or fever due to malignancy, collagen vascular disease or other inflammatory diseases. The commonest cause of fever seen by the generalist is acute viral or bacterial infection. Fever is caused by the re-setting of the hypothalamic thermostat by pyrogens. These are toxins or bacterial lipopolysaccharides (components of the bacterial wall), antigen-antibody complexes and components of the complement system. These pyrogens stimulate immune cells to release pyrogenic cytokines which raise the hypothalamic “thermostat” resulting in our body producing more heat. The end result of this process is fever. Antipyretics act by reducing the production of prostaglandins, thus lowering the hypothalamic set point. They don’t reduce normal body temperature. Fever inhibits viral and bacterial growth as well as enhancing certain components of the immune system, and is a key part of our immune response to fend off infection.1
Fever is one of the commonest reasons for a parent coming to your office with their child. At the same time, fever is generally the result of a relatively benign viral illness in the “daycare crowd” — less than 1% of children in a primary care setting will have a serious illness.2 So anxiety is often the first thing to address. Many parents suffer from “fever phobia” and need to be reassured that fever is not necessarily bad, nor does it always require treatment.
The height of the fever is not all that helpful in a GP’s office where the prevalence of serious infection is low. In that setting, temperatures greater than 40°C increase the likelihood of serious disease from 0.8% to 5.0%.3 There’s an excellent handout for parents in Pediatrics in Review which is worth having in your office, especially for your new parents.4
The majority of fevers are caused by minor viral infections that are self-limited with temperature rarely elevated for more than 24-72 hours. Most issues regarding fever in the 2-36-month range can be settled by a good history and physical examination. Viral infections are more likely if there are other family members ill, or if the child attends daycare. But, as always, there are caveats…
First red flag: Any infant 0-2 months of age with fever needs to be investigated, as infants in this group may have a serious bacterial infection (10%), usually a urinary tract infection, but occasionally meningitis (3%).5 These children need to be referred to the emergency room.
Second red flag: In a child with fever without an obvious cause, you need to rule out a urinary tract infection. In this age range, you may screen with a bag but if the bagged specimen is positive on microscopy and/or dipstick, it’s necessary to obtain a catheterized specimen. Bagged specimens are unreliable for culture because of the high incidence of contamination. With the introduction of vaccines against H. influenzae type B and Streptococcus pneumoniae, we’re less concerned about occult pneumococcal bacteremia in the older group (2-36 months).6
Third red flag: If a kid in whom you have diagnosed a viral infection develops fever after two or three days, he should be seen to rule out bacterial complications of viral infections such as otitis media and pneumonia.
Fourth red flag: Any child in this age range who has fever and appears sick to you needs further investigation.7
Fifth red flag: I’m always alert to parents; if they feel their kid is unusually sick as well as having fever, then investigations may be indicated. In the study mentioned in reference 2, in a primary care setting where the prevalence of serious bacterial infection is low, the clinician’s suspicion and parental concern that there could be a serious infection had positive likelihood ratios of 23.5 and 14.4, respectively.8
Sixth red flag: Although meningitis and other serious infections are uncommon, I always ask myself the question, “could this be…?” remembering that if you don’t think about it, you won’t make the diagnosis.
Finally, remember that the best weapon in your armamentarium is the ability to follow up the patient by telephone or in the office to re-assess. This ability is what makes primary care, or as I prefer to call it, continuity of care so critical.
To sum up, fever in primary care pediatrics is a common presentation and is usually due to a self-limited viral infection. An astute history and focussed physical examination will provide the diagnosis in the majority of cases. In low prevalence situations such as primary care, clinical intuition and parental concern that this child has a serious infection may be correct. Remember always that the 0-2-month-old infant is in a separate category in which fever more often indicates a serious bacterial infection requiring evaluation in the ER.