CHAPTER 16 Fever
There are three types of fevers, each caused by a specific pathophysiological process. The first involves the raising of the hypothalamic set point. The receptors in the area of the hypothalamus regulating body temperature are triggered to reset at a higher core body temperature. This results in an elevation of the helper T-cell production and an elevation in the effectiveness of interferon. Infection, collagen disease, vascular disease, and malignancy are commonly responsible for these fevers.
A second type of fever is a result of heat production exceeding heat loss. Here the set point is normal, and heat loss mechanisms are active. Fever occurs either because the body raises its metabolic heat production or because the environmental heat load exceeds normal heat loss mechanisms. Aspirin overdose, malignant hyperthermia, hyperthyroidism, or hypernatremia may cause this type of fever.
A third type of fever is caused by a defective heat loss mechanism that cannot cope with normal heat load. Heat stroke, poisoning with anticholinergic drugs, ectodermal dysplasia, and burns are causes of this kind of fever.
For the first type of fever, antipyretics are given to lower the hypothalamic set point. Antipyretics are ineffective for the second and third types of fever.
Diagnostic reasoning: focused history
Occurrence of fever
Fever is a common presenting problem and a cardinal manifestation of disease. Patients often report a subjective fever (i.e., clinical symptoms, such as flushing, chills, shaking chills, headache, malaise, or muscle aches) that is assumed by the patient to be a fever although not validated with a thermometer. Nevertheless, the absence of fever in a single patient visit does not eliminate a febrile illness.
Measurement of temperature
Many people use touch to determine whether a fever is present. Although not a precise indication, touch can signal a high fever. During the early stages of fever, perfusion to the skin is decreased and skin temperature falls. In later stages, when temperature within the muscles has risen significantly, increased body temperature is reflected by increased skin temperature. In children, hands and feet should not be used to gauge a fever because they may be vasoconstricted and feel cold. Accurate temperature should be measured using a thermometer. Because of the diurnal variation in normal body temperature and the effect of physiological factors and body rhythms, frequent recordings throughout the day are needed to monitor fever.
Head trauma, otitis media, and contact
Recent head trauma, especially at the base of the skull, may provide an entrance for infectious organisms. Children with recurrent or chronic otitis media may have mastoiditis spreading to the meninges. Contact with anyone with meningococcal disease and/or Haemophilus influenzae places the individual at risk for contracting the disease.
Headache, vomiting, lethargy, or stiff neck
Meningitis is characterized by headache, fever, lethargy, confusion, vomiting, and stiff neck. However, the presentation is highly variable. Any patient with even minimal neurological signs and symptoms should be evaluated for meningitis.
Infant
Fever in children less than 2 months of age is uncommon but must be viewed as serious. Generally neonates and young infants are less able to mount a febrile response; when they do, it is a significant finding. Fever can be viral or bacterial in nature. Fevers in the neonate may also be an indication of an underlying anatomical defect. Urinary tract infection and bacteremia are often the first indications of a structural abnormality of the urinary tract. Also, infants with galactosemia may present in the first weeks to 1 month of life with gram-negative sepsis. Occasionally, infants present with sepsis associated with delivery (prolonged rupture of membranes); acquired from instrumentation used during delivery, such as scalp electrodes; or from a procedure performed in a neonatal intensive care unit.
All infants younger than 2 months with fever are considered to have sepsis or meningitis until proven otherwise.
Duration of fever
In adults, fevers from an acute process usually resolve in 1 to 2 weeks. Fevers that last 3 weeks or longer, that exceed temperatures of 38.4° C (101.1° F), and that remain undiagnosed after 1 week of intensive diagnostic study are classified as FUOs.
Fevers in children can be grouped into three categories: short-term fever, fever without localizing signs, and fever of unknown origin. Short-term fever is defined as a fever of short duration, readily diagnosed, that resolves within 1 week. Fever without localizing signs is a fever with no localizing sign and of brief duration (usually <10 days) that is not explained by findings on history or physical examination. FUO is a fever usually greater than 38.5° C (101.2° F) that lasts longer than 2 weeks on more than four occasions.
Height of fever
Dehydration and febrile seizures are related to the height of the fever. Generally, body temperatures greater than 41.1° C (106° F) are seen in heat illness, central nervous system disease, or either of these in combination with infection. The higher the fever, the greater is the likelihood of bacteremia.
Is the fever caused by a localized infection?
Key questions
Do you have frequency, burning, or urgency with urination?
Are you having unusual vaginal/penile discharge?
Do you have face or sinus pain?
Do you have nasal discharge? If so, what color is the discharge?
Do you have a cough? Is it productive? What color is the sputum?
Do you have any sores (aphthous ulcers) in your mouth?
Are you having any nausea/vomiting or diarrhea?
Location of symptoms
Localizing symptoms will point to the site of the infection. These diagnostic clues include headache or sinus pain, purulent nasal discharge, ear pain, toothache, sore throat, breast tenderness, chest pain, cough, dyspnea, abdominal pain, flank pain, dysuria, vaginal discharge, pelvic pain, rectal pain, testicle pain, calf pain, neck stiffness, joint stiffness, pain or heat, or focal neurological deficits (see appropriate chapters).
Genitourinary tract
Upper urinary tract infection (UTI) in adults commonly produces systemic symptoms with flank pain and fever (see Chapters 17, 31, and 32). Fever with cystitis is uncommon in adults, but children with UTIs present with systemic rather than localized signs and symptoms. UTI is the most common infection in girls younger than 2 years who present with a high fever and in all infants younger than 90 days with fever. Pelvic inflammatory disease in women may cause fever as well as an increased amount of vaginal discharge and bleeding after intercourse. Men who have an acute UTI often present with chills, high fever, urinary frequency and urgency, perineal pain, and low back pain. They may also have penile discharge.
Ear, nose, and throat symptoms
Viral infections of the upper respiratory tract are common and usually produce fever (see Chapters 14, 22, and 29). Otitis media is common in children. Fever may accompany both viral and bacterial pharyngitis. Pharyngitis is frequently manifested only by fever, with the infection localizing 1 or 2 days later. Acute sinusitis can produce a fever. Aphthous ulcers with pharyngitis and cervical lymphadenopathy are seen in children with periodic fevers.
Respiratory or gastrointestinal symptoms
Most febrile illnesses are caused by viral upper respiratory infection (URI), lower respiratory infection (LRI) (see Chapters 10 and 13), or gastrointestinal (GI) tract infection (see Chapter 2). Localized symptoms can help pinpoint the cause of the fever. Vomiting occasionally signals pneumonia.
Joint pain
Joint pain may indicate connective tissue disorders in adults and in children more than 6 years of age (see Chapter 20). Osteomyelitis or septic arthritis may also produce fever.
Skin rash
The prodromal period of a rash is an important historical clue to diagnosis (see Chapter 25). Fever and rash usually appear together 1-5 days after infection. Common eruption periods are as follows:
Ache
Fevers localized to a site without general body manifestations are often bacterial in nature. Fevers accompanied by muscle aches (myalgias), malaise, and/or respiratory symptoms are often viral in nature.
Chronic disease
Chronic conditions and systemic disorders (such as diabetes mellitus, human immunodeficiency virus [HIV], malignancies, neutropenia, and sickle cell anemia) compromise host resistance and increase susceptibility to infection. Prosthetic devices, such as heart valves or joint prostheses, also increase susceptibility to infection.
Health problems, surgery, and recent infection
Current health problems, recurrent infection, or incomplete treatment of infection may be the cause of fever. Such risk factors as diabetes mellitus, neutropenia, and sickle cell anemia heighten the likelihood of bacterial infection. Patients with a past history of infection (such as URI or streptococcal pharyngitis) may be prone to relapse or recurrence. Recent surgical procedures can provide a locus for occult infection; however, a surgical procedure can also induce an inflammatory response, which causes a fever without infection.
Sexual activity
High-risk sexual activity may raise the index of suspicion for HIV infection and additionally for pelvic inflammatory disease (PID) in women.
Immunizations
Children and adults who have not been properly immunized are at greater risk for infectious diseases.
Tuberculosis or hepatitis exposure
Exposure to populations with a high incidence of TB or viral hepatitis increases the risk of infection. Inquire further about constitutional symptoms, such as cough or night sweats (TB) or malaise and abdominal discomfort (hepatitis).
Does the parent report a behavior change in the child?
Key questions
In infants and children, behavior changes may be the only indication that the child is ill. Mildly ill infants may act alert, be active, smile, and feed well. Moderately ill infants may be fussy or irritable but continue to feed, be consolable, and may smile. Severely ill infants appear listless, cannot be consoled, and feed poorly or not at all.
Travel
Patients can be exposed to an emerging infectious disease based on their travel activities. A history of travel out of the country presents the possibility of infection with amebiasis, malaria, schistosomiasis, typhoid fever, or hepatitis A and B. Dengue is the most common vector-borne disease worldwide and is a differential diagnosis for acute febrile illnesses in patients who live or have recently traveled to the tropics or subtropical areas of the United States. Epidemiological surveillance data continually provide updates on patterns of occurrence of infections such as severe acute respiratory syndrome (SARS), avian influenza or “bird flu,” and West Nile virus (see Box 16-1).
Box 16-1 Emerging Infectious Diseases Associated with Fever
Avian influenza (“bird flu”)
A highly pathogenic strain of avian influenza A virus, H5N1, infects birds and mutates rapidly to acquire genes from viruses infecting other animal species. “Bird flu” is transmitted to humans usually through the slaughtering and processing of infected birds. Symptoms of infection can range from flulike symptoms (e.g., fever, cough, sore throat, muscle aches) to pneumonia and severe respiratory distress. Outbreaks that began in Asia in 2003 have spread to parts of Europe. Suspect infection in persons showing flulike symptoms, such as high fever and cough, who have confirmed contact with birds in an area where confirmed outbreaks have occurred. Clinical deterioration is rapid over 4 to 13 days. Laboratory findings include leukopenia, thrombocytopenia, and elevated levels of aminotransferases. Although avian influenza is a rare disease, more than half of reported cases have been fatal and there is great potential for this virus to evolve into a world pandemic.
Sars (severe acute respiratory syndrome)
SARS is a febrile severe lower respiratory tract illness that is caused by infection with SARS-associated coronavirus (SARS-CoV). From 2002 through 2003, the World Health Organization received reports of more than 8000 cases and nearly 800 deaths. No specific laboratory test distinguishes SARS-CoV from other febrile respiratory illness. Lymphopenia and elevated levels of hepatic transaminases, creatinine, and C-reactive protein have been seen in some patients. Diagnosis is based on clinical features (e.g., fever, difficulty breathing, pneumonia) and epidemiologic history of exposure either to a SARS patient or to a setting in which the SARS-CoV transmission is occurring.
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