This question is prompted by but distinct from Is fever (temperature) below 106° F harmful? That question asks about whether fevers below that temperature can cause harm. This question is asking whether there is any appreciable risk of fevers below that temperature progressing to higher temperatures when the underlying cause of fever is a bacterial or viral infection.

That question quotes a source that says in a very definitive tone that fevers caused by viral or bacterial infections do not go above 105 °F:

The common cold and influenza are the most common sources of elevated temperatures.. they can generate fevers that range all the way up to 105 degrees, but [...] Untreated fevers caused by viral and bacterial infections do not rise inexorably and will not exceed 105 degrees [...]

Only in the case of heatstroke, poisoning, or other externally caused fevers is this bodily mechanism over-whelmed and inoperative. It is in those cases that temperatures reach and exceed 106 degrees

(How to Raise a Healthy Child in Spite of Your Doctor, Robert S. Mendelsohn, as quoted in alpha1's question)

Is it true that infections are a negligible cause of elevated body temperature above 105 °F?

  • Are they measuring axillary/forehead, or oral, or rectal/ear temperatures? I've read they range from cooler to warmer readings
    – Xen2050
    Commented Jan 22, 2019 at 23:10
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    I don't think MY experience counts as an expert, but we have had over 26 kids and about half of them have had fevers over 105 due to viral or bacterial infection. Usually related to simple child ailments like ear infections being untreated.
    – coteyr
    Commented Jan 23, 2019 at 6:12
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    The claim that bacterial infections cannot cause “high“ fever while poisoning can is already fallacious because many bacteria produce harmful toxins while they infect the human body. That’s what happens during sepsis. Viral infections can at least weaken the immune system as to allow bacterial superinfection in which case the first sentence applies. Commented Jan 23, 2019 at 10:49
  • The author was also an antivax activist. Why he went nuts after a fairly standard medical education is a great question. His fairly early death (aet. 62) is indeed ironic. Commented Jan 29, 2019 at 19:30

1 Answer 1


The claim is false, as evidenced by Prospective Evaluation of the Risk of Serious Bacterial Infection in Children Who Present to the Emergency Department With Hyperpyrexia (Temperature of 106°F or Higher) Pediatrics, July 2006; 118(1): 34–40.

Data were collected prospectively on all children <18 years of age presenting to a pediatric emergency department during a 2-year period with rectal temperatures of ≥106°F


Of 130 828 visits, 103 children had hyperpyrexia (1 per 1270 patient visits). Of the 103 subjects, 20 had serious bacterial infection, and 22 had laboratory-proven viral illness (including 1 subject with bacterial/viral coinfection)


Common causes of hyperpyrexia in children include bacterial infections, viral infections...


One subject, a 4-year-old boy with muscular dystrophy, presented with both neuroleptic malignant syndrome and apparent septic shock. His temperature reached 108.9°F, and he expired during subsequent hospitalization despite aggressive management. A tracheal aspirate collected in the ED grew Pseudomonas. Because the same organism was recovered from autopsy blood cultures, the Pseudomonas was regarded as the cause of sepsis.


no child arrived in the ED with hyperpyrexia secondary to heat-related illness

  • 2
    Thanks. I'd appreciate if you could add some more info about how to distinguish correlation from causation in this area, if possible. Does "cause of sepsis" in that last quote imply "cause of fever"? I looked up "neuroleptic malignant syndrome" and it seems to be a drug reaction that can cause dangerously high fever.
    – paradisi
    Commented Jan 22, 2019 at 19:43
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    The authors seem to be a bit vague in most places about causality, as the abstract talks about "the risk of serious bacterial infection in children with hyperpyrexia" (rather than e.g. "the risk of hyperpyrexia in children with serious bacterial infection") and they say both that "Common causes of hyperpyrexia in children include bacterial infections, viral infections, neuroleptic malignant syndrome, intoxication, and heat stroke" and "whether or not hyperpyrexia itself confers a high risk for serious bacterial infection (SBI) is a controversial issue".
    – paradisi
    Commented Jan 22, 2019 at 19:44
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    @sumelic "incidence of SBI in children without underlying illness was 13" and "We suspect that viruses may have been responsible for many of the nonspecific febrile illnesses"
    – DavePhD
    Commented Jan 22, 2019 at 20:16
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    When I was about 10 years old I was hospitalized with a case of pneumonia. When they'd checked me in and had me in a bed they checked my temp. It was 108. Commented Jan 22, 2019 at 22:33
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    @DavePhD - What they called a "sponge bath" -- wrapping my body in towels that I suspect had been soaked in alcohol. I recall the nurse telling me that when she started out they would have put me in a tub of ice water. Commented Jan 23, 2019 at 0:47

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