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Article Review:
Pediatric Infectious Disease specialists from Kaiser Permanente reviewed medical records on 160,818 term infants to determine the microbiologic etiology of bacterial infection. Ages of the infants studied ranged from 7 to 90 days of life. From 2005-2009, all blood cultures drawn from these infants from the Emergency Room and upon admission were reviewed. Infants with other known medical problems including prematurity were excluded from this study.
A total of 4,255 blood cultures were taken from these infants over 5 years. 93 blood cultures (2%) of these were true pathogens and 6% were considered contaminants. The overall incidence of bacteremia was 0.57/1,000 live births. Of the 93 positive blood cultures, E. Coli was found in 56% of the cases, Group B Streptococcus 21%, Staphylococcus aureus (8%), and Streptococcus pneumoniae (3%).
Of the 48 infants whose blood cultures were positive for E. Coli, all but one had a positive urine culture with E. Coli. In addition, of these 48 infants, 38 had a lumbar puncture performed of which 4 infants (11%) had a positive CSF culture for E. Coli.
Of the infants who were positive for Group B Streptococcus, 17 had a lumbar puncture performed and 5 of these (29%) had a positive CSF culture for Group B Streptococcus.
The authors also note that 36% of all pathogens identified were ampicillin resistant.
Listeria infection was not found in this study group, and thus the authors conclude that ampicillin may no longer be necessary when empirically treating these infants, while awaiting culture results.
COMMENTARY From Arnd Herz, MD, co-author and Pediatric Infectious Disease Specialist:
In our study, the majority (72%) of “positive blood cultures” represent a blood culture contamination, rather than true infection. This allows us to put things into perspective as we council parents when we re-evaluate the infant. However, an initial positive blood culture result (before further details are available) increases the likelihood of the infant being truly bacteremic, compared to the a priori risk for the same age febrile infant, by 14-fold (from 2% to 28%). Thus all infants with a first report for a positive blood culture deserve an immediate re-assessment. Repeating a blood culture is rarely helpful to distinguish a blood culture contamination from a clinical significant pathogen, as that distinction is made solely on clinical grounds and the ultimate identification of the organism growing in the initial blood culture bottle.
Knowing the most common causes of bacteremia should help in directing our care. All febrile infants need an examination of their urine, as a urinary E. Coli is the most likely source of any bacteremia. Early-onset Group B Streptococcal disease has been reduced by maternal antibiotic treatment intrapartum, but late-onset disease is still present. Maternal GBS status or treatment is not predictive for late-onset disease. Given the relatively high rates of meningitis for bacteremic infants, all infants deserve a lumbar puncture prior to initiation of antibiotics.
Finally, it is helpful to remember that Listeria and Enterococcus are exceedingly rare in our population and therefore antibiotic choices can be tailored to commonly encountered bacteria. Ampicillin (or Penicillin) or a Cephalosporin treat Group B Streptococcus effectively. An aminoglycoside or a higher-level Cephalosporin will treat E. coli and most other Gram-negative organisms. However, we should not forget that 8% of pathogens were S. aureus, and while we presently did not have a single case of MRSA, this is a real concern for the future, as routine choices of antibiotics do not usually cover this organism well.
In summary, Ampicillin and Gentamicin still cover all commonly encountered bacteria in this age group. A third generation Cephalosporin alone would be equally efficacious, as would an aminoglycoside alone for a Gram-negative organism. A gram-positive organism very frequently represents a contaminant; however, in a sick child it may also be the first case of MRSA and may need empiric coverage with Vancomycin and Gentamicin.
http://pediatrics.aappublications.org/content/early/2012/02/22/peds.2011-1546
http://pediatrics.aappublications.org/content/early/2012/02/22/peds.2011-1546
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