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Diagnosing fever by touch: observational study

BMJ 1998; 317 doi: (Published 01 August 1998) Cite this as: BMJ 1998;317:321

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The Definition of Fever

The Definition of Fever

Ms Whybrow, Mr Murray and Prof Morley's paper provides important and useful information (1 August 1998). However, we did not define fever as a temperature of 37.4 °C or more in our paper [1]. In fact, we stated that, "Normal body temperature is not fixed; it varies from person to person, and also varies by about 1°C in the same person at different times of the day [2]. It increases during the first seven months of life and falls again between 24 and 36 months, so the 95% confidence interval for rectal temperature in the first three years of life is 36.6 °C to 38.4 °C [3]. The definition of fever is therefore arbitrary, and great precision in the measurement of temperature is rarely necessary."

Presumably, Whybrow et al arrived at a figure of 37.4 °C as our definition of fever by taking the upper 95% confidence interval for rectal temperature of 38.4 °C that we mentioned in passing (from a 1937 study in California) and used our conversion factor of 1.0 °C (from a 1980s study in Papua New Guinea) to obtain an axillary temperature of 37.4 °C. Fever is not an all or nothing phenomenon, and it is not sensible to say that X °C is a fever and X - 0.1 °C is not; 37.5 °C may be the upper limit of normal in one person, but another may have a normal range of 37.5-38.5 °C.

Whybrow et al speculate that our definition of fever may have differed from theirs because we left the thermometer in place for less than three minutes. In fact, as we stated in our Methods section, we tested the equilibration speed and the calibration of our electronic and glass thermometers in a water bath before the study. Did Whybrow et al do this? Was their thermometer accurate?

[1] Shann F, Mackenzie A. Comparison of rectal, axillary and forehead temperatures. Arch Pediatr Adolesc Med 1996;150:74-78.
[2] Mills JN. Development of circadian rhythms in infancy. In: Davis JA, Dobbing J, eds. Scientific foundations of paediatrics. London: Heinemann; 1974:761.
[3] Bayley N, Stolz HR. Maturational changes in rectal temperatures of 61 infants from 1 to 36 months. Child Dev 1937;8:195-206.

Frank Shann
Professor of Critical Care Medicine
Royal Children's Hospital, Melbourne, Vic 3052, Australia

Competing interests: No competing interests

31 July 1998
Frank Shann
Director of Intensive Care
Royal Children's Hospital, Melbourne