| Abstract | BACKGROUND: Neonatal sepsis is a low incidence, high-risk disease with many sepsis
work-ups performed to detect a single case. Seventy-two hours of antibiotic therapy have
been traditionally recommended pending negative culture results. Improved culture media
and new technology integrated into blood culture systems could shorten incubation time
required to detect positive culture results. This would then change the length of antibiotic
therapy in the management of the newborn infant with suspected sepsis. In addition,
previous data supporting the 72-hour recommendation were retrospectively acquired, utilized
nonautomated systems, and reported in an era with a different population of microorganisms
cultured in special care nurseries. OBJECTIVE: Evaluate the time of incubation to detect
positive blood cultures from newborn infants with suspected sepsis using a
computer-assisted, automated blood culture system, ESP (Trek Diagnostic Systems, Inc,
Westlake, OH). DESIGN: Prospective, observational study. PATIENTS AND SETTING:
All positive blood culture results that were obtained from term and preterm newborn infants
born from November 1993 through June 1997 at a publicly funded hospital with over 6000
live births per year. METHODS: As positive blood culture results were identified, data were
prospectively obtained from the patient's medical record. The computer algorithm in the
automated blood culture system determined the time to positivity. Time to positivity was
determined for blood cultures obtained before the initiation antimicrobial therapy and
compared with those cultures obtained after beginning therapy. Time to positivity was also
evaluated for clinically important Gram-positive and Gram-negative bacteria and yeast.
RESULTS: Four hundred fifty-five positive blood culture results were obtained from 222
patients. Gram-positive organisms accounted for 80% (366/455) of the positive culture
results, Gram-negative organisms accounted for 11% (48/455), and yeast for 9% (41/455).
Virtually all cultures growing clinically significant Gram-positive and Gram-negative
organisms were positive by 24 to 36 hours of incubation. Cultures growing Staphylococcus
epidermidis were virtually all positive after 36 to 48 hours of incubation. Of cultures growing
yeast, 88% (36/41) were positive by 48 hours of incubation. There was no difference in time
to positivity in pretherapy or posttherapy obtained positive blood cultures. Prenatally
administered antibiotics did not affect time to positivity in positive cultures drawn on the first
day of life. In a selected group of microorganisms that are the frequent cause of bacteremia
in term infants, 97% and 99% of cultures were positive by 24 to 36 hours of incubation
when only pretherapy cultures are evaluated. CONCLUSIONS: The ESP blood culture
system identified 77%, 89% and 94% of all microorganisms at 24, 36, and 48 hours of
incubation in aerobic cultures obtained from both term and preterm infants. Introduction of
antimicrobial therapy did not affect time to positivity. Reducing duration of antibiotic therapy
to 24 to 36 hours should be considered in term, asymptomatic newborn infants undergoing
evaluation for suspected sepsis for maternal indications. Confirmation of similar rapidity of
detection using other blood culture systems should be undertaken. |