Occult (hidden) bacteremia is the presence of bacteria in the bloodstream of a child who has a fever but who looks well and has no obvious source of infection.
Most commonly, occult bacteremia is caused by Streptococcus pneumoniae bacteria.
Typically, children have no symptoms other than fever.
The diagnosis is based on blood tests.
Antibiotics can eliminate the infection.
Vaccination can prevent infection by Streptococcus pneumoniae.
(See also Bacteremia in adults.)
Children 3 months to 3 years of age commonly develop fevers. Most of the time, they have other symptoms, such as a cough and runny nose, which help doctors diagnose the cause of the fever. Sometimes, however, children have fever and no other symptoms. That is, they have a fever with no apparent source or cause. In most of these children, the fever is caused by a viral infection that goes away without treatment. In some children, a urinary tract infection is present. In a few children who have fever with no obvious cause, the fever is caused by bacteria circulating in their bloodstream (bacteremia). Circulating bacteria are almost never the cause of fever in older children or adults who have no other symptoms.
In the United States and Europe, vaccination of infants with the Haemophilus influenzae type b conjugate vaccine and the Streptococcus pneumoniae conjugate vaccine has nearly eliminated occult bacteremia caused by these bacteria in vaccinated children. Vaccines against Neisseria meningitidis are given routinely to preadolescents and adolescents and also can be given to certain children under 36 months of age who have an increased risk of infection. Children who have received their recommended vaccines are very unlikely to develop occult bacteremia. However, occult bacteremia can still occur in children who have received no vaccines or not enough doses and in children who have an impaired immune system.
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(See also Overview of Bacterial Infections in Childhood.)
Symptoms of Occult Bacteremia
The major symptom of occult bacteremia is
Fever higher than or equal to 102.2° F (39° C)
Children who have other symptoms, such as cough, shortness of breath, little or no interest in anything (listlessness), or red or blue discoloration of the skin, are not considered to have occult bacteremia. They most likely have a specific bacterial infection and should be evaluated by a health care professional right away.
Diagnosis of Occult Bacteremia
Blood culture
Urine culture and urinalysis
Sometimes other blood and stool tests and a spinal tap
Because doctors cannot tell with certainty which children who have a fever have occult bacteremia, doctors need to identify any bacteria by doing a blood culture. Because the bacteria are too few or too small to see, doctors send samples of blood to the laboratory so the bacteria can be examined and grown (cultured) for identification. If the culture results are positive, it means bacteria have been found.
Infants or children of any age who have a fever and who appear seriously ill, regardless of whether they have received vaccinations, have samples of blood, urine, and cerebrospinal fluid (fluid from around the brain and spinal cord) taken for testing. The fluid is removed during a spinal tap (lumbar puncture), which involves withdrawing a sample of fluid from the space between 2 vertebrae using a small needle. All samples are sent to a laboratory for testing to look for signs of bacterial infection. In most cases, the infant or child is admitted to the hospital and given antibiotics. Children who have trouble breathing will likely have a chest x-ray as well.
Other blood tests may also be done depending on the age of the child.
Rapid detection tests for certain viruses may also be done in some children. For these tests, a swab is used to take a sample from the nose or throat. The results usually are available within a few hours.
Infants under 3 months of age
As opposed to children 3 months to 3 years of age, when infants under 3 months of age have a fever, doctors cannot always tell just by looking at them whether they could have bacteremia. In these infants, doctors usually do laboratory tests (complete blood count, urinalysis, and blood cultures). If the results of the blood and urine tests seem normal, some doctors have parents or caretakers monitor the infant at home and then return to the doctor's office within 24 hours so the infant can be re-examined and the blood cultures checked. They do not prescribe antibiotics during this time. Other doctors prefer to admit these infants to the hospital and do further tests of the blood, urine, and spinal fluid.
Most doctors consider infants less than 30 days old to be at especially high risk of bacteremia, which has a number of causes. Infants in this age group are typically admitted to the hospital and tests of the blood, urine, and spinal fluid are done. They usually are treated with antibiotics while waiting for results of the laboratory tests.
Infants and children 3 months to 3 years of age
Infants and children in this age group who have a fever but who have complete vaccinations and who appear well are at very low risk of bacteremia. Because of this low risk, doctors may decide to monitor the children without doing blood tests. However, a urinalysis and a urine culture are typically done to look for a urinary tract infection as a cause of the fever. The parents or caretakers are asked to monitor the children's symptoms and follow up with the doctor (by visit or telephone) in 24 to 48 hours. Children who worsen or whose fever does not go away have blood tests and possibly chest x-rays or a spinal tap.
Treatment of Occult Bacteremia
Antibiotics
Children with positive culture results who do not appear very ill are given an injectable antibiotic or antibiotics by mouth at home. Children who have positive culture results and who show signs of serious illness are admitted to the hospital and given antibiotics by vein.
All children who were being observed at home are evaluated again in 24 hours either at a repeat visit or, for certain children depending on their age and other medical circumstances, via telephone. Children who still have fever or who have positive blood or urine cultures and have not been given antibiotics already have more cultures done and are hospitalized. They are then evaluated for serious illness and are given antibiotics by vein.
