FREQUENCY OF LOW-LEVEL BACTEREMIA IN INFANTS FROM BIRTH TO 2 MONTHS OF AGE

Background. The frequency of low level bacteremia (less than or equal to 10 colony-forming units/ml) in infants from birth to 2 months of ag e and the optimal volume of blood and number of blood cultures to be c ollected have not been well-documented. During 1991 guidelines at this hospital for collection of blood for culture from these infants were revised. Methods. Blood from each infant with suspected bacteremia was usually inoculated into an Isolator 1.5 Microbial Tube(R) (1.5 mi of blood) and a bottle of anaerobic broth (0.5 to 3.0 mi of blood). The u se of a second Isolator tube and the total blood volume recommended fo r culture (2 to 6 mi) depended on the weight and total blood volume of each infant. Results. Forty-four bacterial pathogens were recovered f rom the blood of 40 (2.5%) of 1589 infants. Of 34 infants from whose b lood the concentration of pathogens could be determined, 23 (68%) had low level bacteremia. Of 50 isolates of pathogens recovered from Isola tor cultures, 32 (64%) were detected in counts of less than or equal t o 10 colony-forming units/ml. When 2 or 3 blood culture devices were i noculated with a total of 2 to 6 mi of blood from each infant, signifi cantly more cases of bacteremia were detected (34 (3.0%) of 1126 infan ts had positive blood cultures) than when only one culture device cont aining less than or equal to 1.5 mi of blood was used (2 (0.5%) of 398 infants had positive blood cultures; P = 0.008). However, when 4 or m ore culture devices were inoculated with a total of >6 mi of blood fro m each infant (5 (7.7%) of 65 infants had positive blood cultures), th e difference in recovery of pathogens compared with the culturing of f rom 2 to 6 mi of blood per infant was not significant (P = 0.089). Con clusions. Low level bacteremia was common in our infants' patient popu lation. The culturing of up to 6 mi of blood which represented up to 4 .5% of an infant's total blood volume was required for detection of th e pathogens.