What is bacteremia?

Updated: Dec 12, 2018
  • Author: Nicholas John Bennett, MBBCh, PhD, MA(Cantab), FAAP; Chief Editor: Russell W Steele, MD  more...
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Bacteremia is the presence of viable bacteria in the circulating blood. [4] This may or may not have any clinical significance because harmless, transient bacteremia may occur following dental work or other minor medical procedures; however, this bacteremia is generally clinically benign and self-resolving in children who do not have an underlying illness or immune deficiency or a turbulent cardiac blood flow. The concern with occult bacteremia is that it could progress to a more severe local or systemic infection if left untreated. Most episodes of occult bacteremia spontaneously resolve, and serious sequelae are increasingly uncommon. However, serious bacterial infections occur, including pneumonia, septic arthritis, osteomyelitis, cellulitis, meningitis, brain abscesses, and sepsis, possibly resulting in death. [1, 5]

With the development and widespread use of effective vaccines to the common serious bacterial infections of infancy (Haemophilus influenzae type B and Streptococcus pneumoniae), the rate of infectious caused by these pathogens has dramatically declined. Many of the studies in children with occult bacteremia were done prior to the introduction of one or both of these vaccines and, as such, may overestimate the likelihood of occult bacteremia.

Patients with occult bacteremia by definition do not have clinical evidence other than fever (a systemic response to infection). [6] First described in the 1960s in young febrile children with unsuspected pneumococcal infection, bacteremia is defined as the presence of bacteria in the bloodstream of a febrile child who was previously healthy; the child does not clinically appear to be ill and has no apparent focus of infection. [7, 8] Occult bacteremia has been defined as bacteremia not associated with clinical evidence of sepsis (shock or purpura) or toxic appearance, underlying significant chronic medical conditions, or clear foci of infection (other than acute otitis media) upon examination in a patient who is discharged and sent home after an outpatient evaluation. [1]

Often, the only manifestation of occult bacteremia is fever or a minor infection (eg, otitis media, upper respiratory tract infection). [6] Therefore, in a busy clinic or emergency department, infants and young children with occult bacteremia are difficult to distinguish from others in the waiting-room.

Fever is common in pediatric patients. Children average 4-6 fevers by age 2 years. [9] Fever also prompts many visits to the pediatric clinic and emergency department. Approximately 8-25% of doctor's visits by children younger than 3 years are for fever [2, 6, 9, 10] ; 65% of children younger than 3 years visit a physician for acute febrile illness. [10, 11]

Fever is less common in infants younger than 3 months than in those aged 3 months to 3 years. Young infants may not mount a fever response and may also be hypothermic in response to illness or stress. [9] Approximately 1% of infants younger than 2 months present with fever, and fever is twice as common in infants aged 1-2 months as it is in newborns younger than 1 month. [9]

Of all pediatric patients presenting for evaluation of fever, 20% have fever for which the source of infection is undetermined after a history and physical examination. [2] Of all infants and young children who present to the hospital for any reason, 1.6% appear nontoxic, were previously healthy, are older than 3 months, and have a fever without a source (FWS). [2]

Bacteremia may also occur in children with focal infections or in children who have sepsis (ie, clinical evidence other than fever of a systemic response to infection). Children with sepsis generally appear ill, have an increased heart rate or respiratory rate and may have a change in temperature (typically fever, although hypothermia is often seen in very young infants and newborns). Severe sepsis results in hypotension, hypoperfusion, or organ dysfunction. Septic shock occurs in children who do not respond to adequate volume resuscitation or require vasopressors or inotropes. Although bacteria may be present in the bloodstream of children with focal infections, sepsis, severe sepsis, or septic shock, the focus of this article is occult bacteremia.

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