Fever in Adults - Approach to the Patient
Body temperature is controlled by the hypothalamus.
Neurons in both the preoptic anterior hypothalamus and the posterior hypothalamus receive two kinds
of signals: one from peripheral nerves that transmit information from warmth/cold receptors in the skin
and the other from the temperature of the blood bathing the region.
These two types of signals are integrated by the thermoregulatory center of the hypothalamus to
maintain normal temperature. In a neutral temperature environment, the human metabolic rate
produces more heat than is necessary to maintain the core body temperature in the range of
36.5–37.5°C (97.7–99.5°F).
Fever is an adaptive response to both infectious and noninfectious immune system triggers characterized
by a controlled increase in the body's thermoregulatory set point resulting in an elevated body
temperature above normal circadian fluctuations.1
Basal body temperature varies according to circadian rhythm and menstrual cycle with normal body
temperature generally considered 37 degrees C (98.6 degrees F) with variance of 0.5 degrees C-1.0
degrees C.2
37 degrees C (98.6 degrees F)3- > 37.7 degrees C (99.9 degrees F) at any time
Fever Definitions:
● Core temperature > 38 degrees C (100.4 degrees F)
● 2 consecutive temperature elevations > 38.3 degrees C (100.9 degrees F)
● Single oral temperature > 38.3 degrees C (100.9 degrees F) in patients with neutropenia without
evidence of an environmental cause
● Temperature elevation > 38 degrees C for > 1 hour
● Single temperature of > 37.8 degrees C (100 degrees F) in residents of long-term care facility
(LTCF) for predicting infection with 70% sensitivity and 90% specificity
Hyperthermia
● elevation in body temperature without elevation of the thermoregulatory set point1
Hyperpyrexia
● body temperature > 41.1 degrees C (106 degrees F)1
A fever can be:
● Acute if it lasts for under 7 days.
● Subacute if it lasts for up to 14 days.
● Chronic or persistent if it lasts for over 14 days.
Acute Chronic
Differentiated
A B
Undifferentiated
C D
A: Acute differentiated fever
Systems Differentials
Eyes - Conjunctivitis
Rash - scarlet fever,
- measles,
- mononucleosis, and
- Shingles.
- RSV
Ear - Otitis media
- Otitis externa
- Mastoiditis
Oral cavity - Dentine infection
Neck - Meningitis
stiffness - See associated features ( photophobia, phono phobia, kernig, bruduzki signs)
Lymphnodes - Lymphadenitis
Chest - Rheumatic fever
- Endocarditis
- Pneumonia
ENT - Pharyngitis
- Tonsillitis
- Adenitis
- Covid
Bones - Osteomyelitis
Abdomen - Gi infections
- Typhoid
- Gastroenteritis
- Cholecystitis
- Hepatitis
- UTI
Pelvis - GU infections
- PID
Acute Undifferentiated/ localized fever:
- Malaria
- Dengue
- Typhoid
Chronic differentiated fever
Persistent (chronic) fevers are typically defined as fevers lasting more than 10 to 14 days.
ALL SYSTEMIC CAUSES
- TB
- LEPROSY
- BRUCELOSIS
- GOUT
- RA
- MALIGNANCY
Chronic undifferentiated fever/ PUO
History
● Duration of fever
● Residence in or recent travel to an area with malaria transmission
● Recent contact with a person with an infectious disease
● Vaccination history
● Skin rash
● Stiff neck or neck pain
● Headache
● Convulsions or seizures
● Pain on passing urine
● Ear pain.
Examination
General: drowsiness or altered consciousness, pallor or cyanosis, or lymphadenopathy
Head and neck: bulging fontanel, stiff neck, discharge from ear or red, immobile ear-drum on otoscopy,
swelling or tenderness in mastoid region
Chest: fast breathing (pneumonia, septicaemia or malaria)
Abdomen: enlarged spleen (malaria) or enlarged liver
Limbs: difficulty in moving joint or limb (abscess, septic arthritis, osteomyelitis, rheumatic fever)
Skin rash
Pustules, or signs of infection: red, hot, swollen, tender (staphylococcal infection)
Haemorrhagic rash: purpura, petaechiae (meningococcal infection, dengue)
Maculopapular rash (measles, other viral infections)
The term acute undifferentiated febrile illness (AUFI) connotes fever of <14 days duration without any
evidence of organ or system specific etiology.
Dengue, malaria, scrub typhus, enteric fever and leptospirosis have been identified as major causes of
AUFI
Different types of fever
The nature or the type of the fever and the duration should be considered as there are many types
which could help narrow down the differential diagnosis you are considering.
Continuous fever: Where the temperature remains above normal throughout a 24-hour period and
does not fluctuate more than 1° Celsius in 24 hours. This type of fever occurs in lobar pneumonia,
typhoid, urinary tract infection, infective endocarditis, brucellosis and typhus.
Remittent fever: The temperature remains above normal throughout the day and fluctuates more than
2° Celsius in 24 hours. This type is seen in patients with typhoid fever and infective endocarditis.
Intermittent fever: In a 24 hour period the temperature is only present for some hours of the day and
the rest of the time is normal. The spike can occur same time each day, every other day or every few
days but is normally in a repetitive pattern. Examples of some diseases which have intermittent fever
are malaria, pyemia and septicaemia.
Septic fever: A very high temperature which doesn’t improve with antipyretics can indicate a septic fever
and the patient should be seen quickly and reviewed to prevent any further deterioration in their state
of health.
Cyclical recurrent fevers or periodic fevers: These are recurrences of fever which last from a few days to
a few weeks and are separated by symptom free intervals. This pattern of fever can be caused by
recurrent infection, malignancy or non-infectious inflammatory diseases. Attacks of fever which follow
the same course normally have a non-infectious cause like Still’s disease, Rheumatoid arthritis, Crohn’s
disease and Bechet’s syndrome. A family history of periodic fever could indicate Familial Mediterranean
Fever or Hyper-IgD syndrome.
1. Ogoina D. Fever, fever patterns and diseases called 'fever'--a review. J Infect
Public Health. 2011 Aug;4(3):108-24.
2. O'Grady NP, Barie PS, Bartlett JG, et al. Guidelines for evaluation of new fever in
critically ill adult patients: 2008 update from the American College of Critical Care
Medicine and the Infectious Diseases Society of America. Crit Care Med. 2008
Apr;36(4):1330-49, correction can be found in Crit Care Med 2008
Jun;36(6):1992, commentary can be found in Crit Care Med 2008
Nov;36(11):3129.
3. High KP, Bradley SF, Gravenstein S, et al. Clinical practice guideline for the
evaluation of fever and infection in older adult residents of long-term care
facilities: 2008 update by the Infectious Diseases Society of America. J Am
Geriatr Soc. 2009 Mar;57(3):375-94, commentary can be found in J Am Geriatr
Soc 2009 Nov;57(11):2157.
4. Evans SS, Repasky EA, Fisher DT. Fever and the thermal regulation of immunity:
the immune system feels the heat. Nat Rev Immunol. 2015 Jun;15(6):335-49.
5. https://www.aafp.org/pubs/afp/issues/2014/0715/p91.html
6. https://www.aafp.org/pubs/afp/issues/2022/0200/p137.html
