Differentiating culture samples representing coagulase-negative staphylococcal bacteremia from those representing contamination by use of time-to-positivity and quantitative blood culture methods.
Differentiating true coagulase-negative staphylococcal infection from contamination has an important impact on therapeutic implications. Time to positivity reflects bacterial density and may help in the interpretation of blood cultures. We retrospectively reviewed the records of 272 patients from June 2005 to January 2008 for clinical characteristics, microbiological data, and therapeutic outcome. Four groups were identified. The first three groups, as follows, included patients with one positive quantitative blood culture: the low-colony-count group (<10 CFU/ml), the moderate-colony-count group (30 to 100 CFU/ml), and the high-colony-count group (>100 CFU/ml). The control group included patients with two positive quantitative blood cultures and definite coagulase-negative staphylococcal bloodstream infection. The high-colony-count group had shorter time to positivity (< or = 16 h) than did the low-colony-count group (P < 0.0001). The low-colony-count group had a significantly longer time to positivity, >20 h (P = 0.001), than did the moderate-colony-count group. Even though antibiotics were not provided in 71% of cases and central venous catheter was retained in 83%, the low-colony-count group had a favorable outcome, suggesting that <10 CFU/ml represents contamination. The high-colony-count group, similar to the positive control group, required antibiotics in 81% of cases and central venous catheter removal in 51% (P = 0.001). A time to positivity of < or = 16 h reflects high-grade bacteremia with CFU of >100. Similar to the positive control group, these patients required an active therapeutic approach. A time to positivity of >20 h indicates possible contamination with a CFU of <10, and active therapy may not be required.
Kassis
Christelle
C
The University of Texas Health Science Center at Houston, Division of Infectious Diseases, 6431 Fannin, Houston, Texas 77030, USA.
Rangaraj
Gopi
G
Jiang
Ying
Y
Hachem
Ray Y
RY
Raad
Issam
I
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016470:Bacteremia / Q000175:diagnosis* / Q000382:microbiology; D001431:Bacteriological Techniques / Q000379:methods*; D001769:Blood / Q000382:microbiology*; D002648:Child; D003030:Coagulase / Q000096:biosynthesis; D015169:Colony Count, Microbial / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D013203:Staphylococcal Infections / Q000175:diagnosis* / Q000382:microbiology; D013210:Staphylococcus / Q000201:enzymology / Q000302:isolation & purification*; D013997:Time Factors; D055815:Young Adult
D003030:Coagulase
Annu Rev Med. 1999;50:223-36
10073274
Ann Intern Med. 2001 Aug 7;135(3):175-83
11487484
J Clin Microbiol. 2001 Sep;39(9):3279-81
11526163
Infect Control Hosp Epidemiol. 2005 Aug;26(8):697-702
16156326
Clin Infect Dis. 1999 Aug;29(2):239-44
10476719
Clin Infect Dis. 1999 May;28(5):1119-25
10452645
J Clin Microbiol. 1998 Jan;36(1):105-9
9431930
J Clin Microbiol. 1991 Oct;29(10):2245-9
1939578
Clin Infect Dis. 2003 May 1;36(9):1103-10
12715303
J Clin Microbiol. 2006 May;44(5):1834-5
16672415
Clin Infect Dis. 2001 May 1;32(9):1249-72
11303260
J Clin Microbiol. 1985 Aug;22(2):292-5
3897271
Pediatr Infect Dis J. 2003 Nov;22(11):968-74
14614369
J Clin Microbiol. 2002 Mar;40(3):898-901
11880412
J Clin Pathol. 1998 Aug;51(8):635-7
9828828