• 22
    Jan
  • Microbiological surveillance and parenteral antibiotic use: PATIENTS AND METHODS

At the time of the study, Sunnybrook Health Science Centre was a 982-bed (418 acute, 564 chronic), university-affiliated, adult tertiary care teaching hospital in Metropolitan Toronto. It is the largest level 1 trauma centre in Canada, with other major teaching programs that include aging, cardiovascular disease, oncology and trauma. At the time of the study, the CrCU was a 17-bed unit that admitted medical, surgical and trauma patients, the majority of whom required mechanical ventilation.

Data were prospectively collected over a one-year period, May 1, 1995 to April 30, 1996, from all patients admitted to the CrCU for more than one day and who received parenteral antimicrobial therapy. Information collected by daily chart re­view included site of infection, culture and antimicrobial sus­ceptibility test results and length of stay. Duration of par­enteral antibiotic usage, as well as total antibiotic acquisition costs, were also recorded.

The diagnosis of infection and choice of antimicrobial ther­apy were at the discretion of the medical staff in the CrCU. There was, however, significant input into antimicrobial pre­scribing by the Departments of Pharmacy, Microbiology and Infectious Diseases. This included daily attendance at patient rounds by a clinical pharmacist and weekly rounds with a mi- crobiologist. Table 1 includes all formulary antibiotics that were available for use in the CrCU. The medical staff in the CrCU was not aware that the audit was being performed.

Bacterial isolates were from all body sites (both sterile and nonsterile) and data recorded on these isolates were collected once the diagnosis of infection was made by the CrCU staff. No standard definitions of infection were used. Table 2 indicates the categories of infections as used by the medical staff in the CrCU. Bacteremias were recorded as primary (no obvious source) or secondary.

TABLE 1 Parenteral antibiotic usage in the critical care unit at Sunnybrook Health Science Centre, Toronto, Ontario from May 1,1995 to April 30,1996

Antibiotic

Number of
patients
(%)
receiving antibiotic
(n=258)

Average g/patient
day

Total use (gV

Total cost
($)*

Penicillins

Penicillin

10 (3.9)

10.9 units

906 units

322.80

Ampicillin

37 (14.3)

2.1

1028

686.40

Cloxacillin

43 (16.7)

3.1

1913

1161.25

Piperacillin

28 (10.9)

5.4

2879

8990.00

Cephalosporins

Cefazolin

120 (46.5)

1.8

1098

2709.46

Cefuroxime

41 (15.9)

1.1

323

3116.67

Cefotetan

14 (5.4)

0.8

58

840.00

Ceftriaxone

52 (20.2)

0.7

255

8634.00

Ceftazidime

24 (9.3)

0.8

265

4028.00

Carbapenems

Imipenem

0

0

0

0

Aminoglycosides

Gentamicin

86 (33.3)

0.2

141

5088.46

Tobramycin

32 (12.4)

0.1

81

6025.44

Amikacin

1 (0.4)

0.05

2.5

146.25

Quinolones

Ciprofloxacin

20 (7.8)

0.3

49

4384.02

Miscellaneous

Erythromycin

19 (7.4)

1.7

178

1052.25

Vancomycin

38 (14.7)

0.5

256

5370.36

Clindamycin

48 (18.6)

1.0

459

3666.05

Metronidazole

49 (19)

0.6

209

589.36

Trimethoprim/

17 (6.6)

6.5 mL

1590 mL

1113.00

Susceptibility testing of microorganisms was done accord­ing to recommended National Committee for Clinical Labora­tory Standards (NCCLS) guidelines. The automated Vitek bacteriology system (bioMerieux Vitek Inc, Hazelwood, Mis­souri) was used for the identification of microorganisms and susceptibility testing. Detection of MRSA was confirmed using an oxacillin screen plate containing 6 g oxacillin and 4% so­dium chloride. VRE were detected according to the method of Jorgensen et al, using 6 g of vancomycin (Sigma Chemi­cal Company, St Louis, Missouri) in brain-heart infusion agar (Difco Laboratories, Detroit, Michigan). Detection of extended-spectrum beta-lactamases (ES6L) was made only on Escherichia coli and klebsiella strains isolated from sterile body fluids, using the E-test (CAB Biodisk, Solna, Sweden) strips with a combination of a beta-lactam and beta-lactamase inhibitor.

TABLE 2 Indications for antimicrobial therapy

Indication

Number (%)

Pneumonia

121 (35.6)

Prophylaxis

114 (33.5)

Bacteremia

30 (8.8)

Primary

20 (5.9)

Secondary

10 (2.9)

Intra-abdominal infection

23 (6.8)

Skin/soft tissue infection

12 (3.5)

Urinary tract infection

10 (2.9)

Line-associated infection

5 (1.5)

Surgical wound infection

4(1.2)

Other (sinusitis, meningitis, endocarditis,

21 (6.2)

Data collected from patients were entered and analyzed us- ingFilemaker Pro (Claris Corporation, Santa Clara, California). Descriptive statistics were performed on the data presented. Length of stay data were reported as mean standard devia­tion. A Student’s t-test was used to compare the length of stay of patients who received antibiotics with all patients admitted to the CrCU during the period of audit.
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