patient with fever
  • According to studies of healthy individuals 18 to 40 years of age, the mean oral temperature is 36.8°± 0.4°C (98.2°± 0.7°F),
  • with low levels at 6 A.M. and higher levels at 4 to 6 P.M.
  • The maximum normal oral temperature is 37.2°C (98.9°F) at 6 A.M. and 37.7°C (99.9°F) at 4 P.M.
  • These values define the 99th percentile for healthy individuals

Pathophysiology of fever

Three pathophysiologic bases exist
1.  The raising of the hypothalamic set point in the CNS:

  • Infection, collagen vascular disease, and malignancies
  • are lowered by antipyretics and physical removal of heat.

 2.  heat production exceeding heat loss :

  • salicylate overdose, hyperthyroidism, excessive environmental temperature, and malignant hyperthermia.

 3. defective heat loss:

  • ectodermal dysplasia, heat stroke, and poisoning via anticholinergic drugs.
  • Antipyretics are ineffective for the second and third types of fever.

Types of Fever

—Intermittent fever is an exaggerated circadian rhythm that includes a period of normal temperatures on most days; extremely wide fluctuations may be termed septic or hectic fever.
—Sustained fever is persistent and does not vary by more than 0.5°C/24?hr.
—Remittent fever is persistent and varies by more than 0.5°C/24.
—Relapsing fever is characterized by febrile periods that are separated by intervals of normal temperature;
Tertian fever occurs on the 1st and 3rd days (e.g., malaria caused by Pl. vivax)
Quartan fever occurs on the 1st and 4th days (e.g., malaria caused by Pl. malaria).
—Diseases characterized by relapsing fevers should be distinguished from those infectious diseases that have a tendency to relapse.

  • A biphasic fever single illness with two distinct periods of fever over 1 or more weeks (camelback fever pattern);  poliomyelitis is the classic example.  leptospirosis, dengue fever, yellow fever, Colorado tick fever and the African hemorrhagic fevers (Marburg, Ebola, and Lassa fever).
  • Periodic fever syndromes with a regular periodicity (e.g., cyclic neutropenia, and periodic fever, aphthous stomatitis, pharyngitis, and adenopathy [PFAPA]

Sign and symptoms

  • A fever occurs when your temperature rises above its normal range.
  • Normal for a person may be a little higher or lower than the average temperature of 98.6 F.
  • Rectal temperature higher than 100.4 F is always considered a fever.
  • A rectal temperature reading is generally 1 F higher than oral reading.
  • Depending on what’s causing fever, additional fever symptoms may include:
    • Sweating
    • Shivering
    • Headache
    • Muscle aches
    • Lack of appetite
    • Dehydration
    • General weakness
    • Very high fevers, between 103 and 106 F, may cause:
    • Hallucinations
    • Confusion
    • Irritability
    • Convulsions


History taking in patient of fever

—Attention  paid to the chronology of symptoms in relation to the use of prescription drugs (including drugs, supplements, or other remedies) or treatments such as a surgical or dental procedure
—A careful history should include exposures to animals; toxic fumes; potential infectious agents; possible antigens; or other febrile or infected individuals in the home or school

Few salient histories

  • Age of the child
  • Grade of fever
  • Type of fever
  • Associated symptoms
  • Duration of fever
  • Any seizure or unconsciousness

Also the history of

  • A history of the geographic areas in which the patient has lived and a travel history
  • Information on unusual hobbies, dietary habits (such as raw or poorly cooked meat, raw fish, and unpasteurized milk or cheeses), and household pets should be elicited
  • Attention should be directed to animal bites; tick or other insect bites; and prior transfusions, immunizations, drug allergies, or hypersensitivities.
  • A careful family history should include h/o tuberculosis, other febrile or infectious diseases, arthritis or collagen vascular disease, or unusual familial symptomatology such as urticaria, fevers and polyserositis, bone pain, or anemia.
  • Ethnic origin may be important For eg, blacks are more likely than persons in other groups to have hemoglobinopathies


  • A meticulous physical examination should be repeated on a regular basis. All the vital signs are relevant.
  • The temperature may be taken orally or rectally, but the site users should be consistent.
  • Axillary temperatures are notoriously unreliable.
  • Special attention should be paid to the
  • skin, lymph nodes, eyes, nail beds, cardiovascular system, chest, abdomen, musculoskeletal system, and nervous system. Rectal examination is imperative. The genitalia should be examined.

Relationship of fever with pulse

Relative tachycardia: due to noninfectious diseases or infectious diseases in which a toxin is responsible for the clinical manifestations.
— Relative bradycardia suggests typhoid fever, brucellosis, leptospirosis, or drug fever.
— Bradycardia in the presence of fever also may be a result of a conduction defect resulting from cardiac involvement with acute rheumatic fever, Lyme disease, viral myocarditis, or infective endocarditis.

Investigations in a patient with fever

  • The workup should include a complete blood count; a differential count should be performed
  • Important to the identification of eosinophils, juvenile or band forms, toxic granulations, which are suggestive of bacterial infection.
  • Neutropenia may be present with :
    • viral infections, particularly parvovirus B19 infection
    • drug reactions
    • SLE
    • typhoid
    • brucellosis and
    • infiltrative diseases of the bone marrow, including lymphoma, leukemia, tuberculosis, and histoplasmosis.
  • Lymphocytosis may occur with typhoid, brucellosis, tuberculosis, and viral disease.
  • Atypical lymphocytes are documented in many viral diseases, including infection with Epstein-Barr virus, cytomegalovirus, or HIV; dengue; rubella; varicella; measles; and viral hepatitis. This abnormality also occurs in serum sickness and toxoplasmosis.
  • Monocytosis is a feature of typhoid, tuberculosis, brucellosis, and lymphoma.
  • Eosinophilia may be associated with hypersensitivity drug reactions, Hodgkin’s disease, and parasitic infections.
    • If the febrile illness appears to be severe or is prolonged:
    • P smear for MP, morphology and the ESR
    • —Urinalysis, with an examination of urinary sediment, is indicated.
    • Any abnormal fluid accumulation (pleural, peritoneal, joint), even if previously sampled, merits reexamination in the presence of undiagnosed fever.
  • Joint fluids should be examined for bacteria as well as crystals.
  • Bone marrow biopsy (not simple aspiration) for histopathologic studies (as well as culture) is indicated when marrow infiltration by pathogens or tumor cells is possible.
  • Stool should be inspected for occult blood; an inspection for fecal leukocytes, ova or parasites may also indicated
Immunocompetent Diagnostic consideration
Neonates (<28 days) Sepsis and meningitis caused by group B Strep   E.coli, Listeria  and  HSV
Infants <3 mo Serious bacterial disease in 10–15% including bacteremia in 5%, of febrile infants
Infants and children 3–36 mo Occult bacteremia in 1.5%; increased  risk with Temp >39°C and  WBCcount>15,000/µL
Hyperpyrexia (>40 C) Meningitis, bacteremia, pneumonia, heatstroke, hemorrhagic shock–encephalopathy syndrome
Fever with petechiae Bacteremia and meningitis caused by N meningitidis, H influenzae type b, and Strep pneumoniae

Immmunocompromised Diagnostic considerations
Sickle cell disease Sepsis, pneumonia, and meningitis caused by S. pneumoniae, osteomyelitis caused by Salmonella (as well as Staphylococcus)
Asplenia Bacteremia and meningitis caused by N. meningitidis, H. influenzae type b, and S. pneumoniae
Complement/properdin deficiency Sepsis caused by N. meningitidis
Agammaglobulinemia Bacteremia, sinopulmonary infection
AIDS S. pneumoniae, H. influenzae type b, and Salmonella infections
Congential heart disease I.E  brain abscess with right-to-left shunting
Central venous line Staph aureus, coagulase-negative staph Candida
Malignancy Bacteremia with gram-ve enteric bacteria, S.aureus, and CONS fungem   with Candida and Aspergillus


  • A fever of >41.5°C (>106.7°F) is called hyperpyrexia.
  • This extraordinarily high fever can develop in patients with severe infections but most commonly occurs in patients with central nervous system (CNS) hemorrhages.
  • In some rare cases, the hypothalamic set point is elevated as a result of local trauma, hemorrhage, tumor, or intrinsic hypothalamic malfunction. The term hypothalamic fever is sometimes used to describe elevated temperature caused by abnormal hypothalamic function. However, most patients with hypothalamic damage have subnormal, not supranormal, body temperatures.

Fever without a focus

common diagnostic dilemma :

  • infants younger than 1 mo.
  • Fever of acute onset and present for less than 1 wk
  • Child younger than 36 months

Infants less than three months of age

  • Serious bacterial infections are present in 10-15% of infants who were born at term and were previously healthy who have rectal temperatures of 38°C or greater.

Causes: sepsis, meningitis, urinary tract infections, gastroenteritis, osteomyelitis, and septic arthritis.

Pyrexia of Unknown Origin

  • a fever documented by a health care provider and for which the cause could not be identified after 3 wk of evaluation as an outpatient or after 1 wk of evaluation in the hospital.
  • Patients with fever not meeting these criteria, and specifically those admitted to the hospital with neither an apparent site of infection nor a noninfectious diagnosis, may be considered to have fever without localizing signs.
  • In most of these children, the development of additional clinical manifestations over a relatively short period confirms the infectious nature of the illness.

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