What is a continuous fever?

A continuous fever is a body temperature greater than 37.7C (100F) that continues to persist for 24 hours or more. While there may be fluctuations in the body temperature during this time, the readings do not return to a normal range.

An acute fever lasts 4 days or less but may continue for up to 7 days in more severe infections. Chronic fevers are usually recurrent fevers that persist over a long period of time. An acute fever may be continuous for the short time span that it persists, however, in most cases the fever is episodic. A chronic fever is intermittent with recurrent episodes of an elevated body temperature lasting for a few hours and then easing only to return again within a short period of time. In contrast, a continuous fever is unrelenting.

Continued Fever Readings

  • Normal body temperature = 36.5C (97.7F) to 37.7C (100F)
  • Fever > 37.7 C (100F)
  • Low-grade fever < 38.3C  (101F)
  • Mild fever = 38.3C (101F) * to 40C (104F )
  • High fever > 40C (104F)

* A temperature above 38.3C  (101F) in an infant younger than 3 months is considered high and should be treated as a medical emergency. Refer to Baby Fever.

Causes of Continuous Fever


Most fevers are caused by an infection. A continuous fever may be indicative of a severe infection that is progressing and serious complications like sepsis may arise.


A continued fever may also indicate damage to the thermoregulatory center in the hypothalamus (central fever) that is responsible for maintaining the body temperature set point. A continued elevation in body temperature may be a result of impairment of the thermoregulatory functions that are responsible for cooling the body.


Drug-induced fever or drug-induced hypothermia that is continuous is most likely due to the chronic use of drugs for the treatment of medical conditions, abuse of illicit drugs due to addiction or unsupervised use of certain drugs like weight loss medication.

Unknown Fever

Unknown fevers may be due to a number of causes with infections accounting for the majority of the cases. An unknown fever is usually a fever that is non-specific, meaning that apart from the raised body temperature, there are no other signs, symptoms or abnormalities detected upon conducting medical tests and investigations.

A fever may be acute or chronic.

Acute Unknown Fever

In the event of an acute fever, signs and symptoms may develop shortly after the onset of the fever thereby assisting with a diagnosis. The cause may be self limiting and resolve spontaneously or may require medical treatment.

Chronic Unknown Fever

A chronic fever that is due to unknown causes is referred to as a fever of unknown origin (FUO). There are certain criteria that define a fever of unknown origin. Therefore, it is important to consult with a doctor and have the necessary tests before defining a chronic fever as a fever of unknown origin.

Fever of Unknown Origin

A fever of unknown origin (FUO) is recurrent episodes of a body temperature greater than 38.3C (101F) that persists for 3 or more weeks with no cause diagnosed after 3 days of inpatient evaluation or more than two outpatient visits.

Article reviewed by Dr. Greg. Last updated on September 9, 2012