Interpretative reporting and selective antimicrobial susceptibility release in non-critical microbiology results

Robert Cunney*, Hiba Abdel Aziz, Darlene Schubert, Eleanor McNamara and Edmond Smyth

Beaumont Hospital and Royal College of Surgeons in Ireland, Dublin 9, Ireland


    Abstract
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 Abstract
 Introduction
 Materials and methods
 Results and discussion
 References
 
The action taken in response to 169 positive sputum, urine and wound culture reports was examined. All reports included interpretative comments. Antimicrobial susceptibilities were released in 29 (17%). Therapy was significantly more likely to be started or altered in response to reports where susceptibilities were released (13 of 29, 45%) versus those without susceptibility release (31 of 140, 22%). Susceptibility release did not influence the appropriateness of antibiotic therapy. The clinical microbiology team was contacted for therapeutic advice in response to 32 (19%) reports. Of the remaining 137 reports, therapy was started or altered in response to 30 (22%) reports, but was considered appropriate in only seven (22%) of these.


    Introduction
 Top
 Abstract
 Introduction
 Materials and methods
 Results and discussion
 References
 
Although restrictive release of antimicrobial susceptibilities is often recommended few studies have evaluated its impact.1

Interpretative reporting of microbiology results entails the addition of a comment to the report, giving the likely significance of the organism(s) isolated and, where necessary, specific advice on therapy. The use of interpretative comments appended to microbiology reports has been shown to allow clinicians to make informed decisions based on such reports.2

This study assessed the impact of these practices in the reporting of positive culture results in hospital in-patients.


    Materials and methods
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 Abstract
 Introduction
 Materials and methods
 Results and discussion
 References
 
At the time of this study, the clinical microbiology team (CMT) in a 650 bed tertiary-referral centre comprised one consultant and two senior registrar grade microbiologists. Information technology support is provided by a Gerber Alley/First Data integrated hospital/laboratory system (HBO & Co., Charlotte, NC, USA). Test request, laboratory processing, result verification and reporting are carried out on computer terminals. Programmed pre-set interpretative comments are automatically added to some positive reports (e.g. highlighting the need for infection control precautions for isolates of methicillin-resistant Staphylococcus aureus). Bar-coded and free text comments are also added manually by the CMT, who verify all positive results before release.

Limited antimicrobial susceptibilities are released only if the isolate, specimen type and clinical details suggest a need for therapy. The pager and telephone extension numbers of the CMT are provided on all reports. Susceptibility results can be obtained around the clock by contacting the CMT member on-call, who can access the laboratory computer system via a modem link.

The responses to positive urine, sputum and wound/soft-tissue culture results for 169 in-patients were assessed. Reports on patients in the intensive care unit, who are reviewed daily by the CMT, were excluded from this study as were other patients seen on consultation. Positive reports from normally sterile and/or deep tissue sites were also excluded, as the CMT discussed these results directly with the relevant clinician via telephone contact and/or ward visits.

Patient charts and nursing notes were reviewed within 24 h of the report being issued and again 5 days later by two of the authors (H.A.A. and D.S.). Indications for sending the specimen were divided into symptomatic (i.e. specimen taken in response to a presumed infective episode) and asymptomatic (i.e. no precipitating infective episode). The response to the report was considered appropriate if the report prompted the clinician to contact the CMT or if antibiotic therapy was started or altered according to the susceptibilities given in patients with a clinical indication for therapy. If no therapy was given in patients without a clinical indication the response was also considered appropriate. The appropriateness of antibiotic therapy was independently assessed, in the light of the hospital antibiotic policy, by two of the authors (R.C. and E.M.).

Proportions were analysed using the {chi}2 test, with Fisher's exact test where a cell value was less than or equal to five. Statistical analysis and power calculations were carried out using Epi-Info (CDC, Atlanta, GA, USA, version 6.04).


    Results and discussion
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 Abstract
 Introduction
 Materials and methods
 Results and discussion
 References
 
The mean age of the 169 patients was 61 years with a male/ female ratio of 47/53. The types of specimens and responses to the reports are shown in Table IGo. Therapy was significantly more likely to be started or altered, and more likely to be appropriate, for reports on specimens sent in response to a presumed episode of infection, compared with those sent from asymptomatic patients.


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Table I. Nature of specimens and therapeutic responses to the report issued (n = 169)
 
Ninety-four (56%) specimens were taken from asymptomatic patients, of which only four (4%) prompted appropriate antibiotic therapy. This compares with the findings of Spencely et al.3 that 43% of specimens were for ‘screening’ purposes and 29% of these were thought to affect patient management. In our study 41 of 94 such specimens were generated by routine nursing care (e.g. a wound swab taken during a dressing change), compared with 12 of 75 specimens from symptomatic patients (RR 2.73, 95% CI 1.55–4.81, P < 0.001).

The type, and examples, of interpretative comments used are shown in Table IIGo. Clinicians were significantly more likely to contact the CMT in response to reports in which non-antibiotic therapeutic advice was given (RR 2.72, 95% CI 1.15–6.48, P = 0.03), or where the isolate was multiply resistant (RR 3.48, 95% CI 1.87–6.48, P < 0.001), compared with other comments.


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Table II. Types and examples of interpretative comments appended to the 169 reports of positive cultures
 
Rates of inappropriate antibiotic therapy of 60% for asymptomatic catheter bacteruria and 80% for upper airway colonization have been reported when antibiotic susceptibilities are unrestricted.2,4 This compares with corresponding rates of 23% and 11% in our study. In addition, advice was sought from the CMT in response to 32 (19%) reports and antibiotics were started or continued in 13 (41%) of these instances. The fact that almost one-fifth of reports prompted such contact is significant considering that reports from normally sterile/deep tissue sites and patients known to the CMT were excluded. Such consultation with the CMT early in the course of infection has been shown to increase compliance with therapeutic advice and improve outcomes.5,6

Of the 137 reports where the CMT was not contacted therapy was started or altered in 30 (22%), but was considered appropriate in only seven (22%). In 21 cases no action was taken in response to the report, despite an indication to do so. In 19 of these cases there was an indication to stop or narrow antibiotic therapy and in two cases an indication to start antibiotics was ignored, despite release of susceptibilities in the latter cases.

Antibiotic susceptibilities were released on 29 (17%) reports with a mean of three appropriate susceptibilities released per report. Therapy was significantly more likely to be started or altered in response to the 29 reports in which susceptibilities were released (12; 41%) compared with the 140 where susceptibilities were withheld (31; 22%) (RR 2.07, 95% CI 1.08–3.97, P = 0.03). This may reflect a tendency to consider reports that include susceptibilities as warranting treatment, regardless of clinical indications. The therapy started in response to reports (n = 43) was considered appropriate in six of 12 (50%) where susceptibilities were released, compared with 15 of 31 (48%) where susceptibilities were suppressed (RR 1.05, 95% CI 0.4–2.74, P = 0.9). The lack of impact of susceptibility release on the appropriateness of therapy may be due to the small number of reports in the study that had susceptibilities released (29 of 169). The study had an 80% power to detect a 1.67-fold difference in appropriate therapy between the two groups. This may also reflect the use of hospital antibiotic policy as a basis of assessment, and thus a narrow definition of appropriate therapy. Susceptibilities were released on reports only where there was an apparent indication for therapy, which would be expected to increase the appropriate prescribing in this group. Further restriction of susceptibility release, encouraging more discussion with the CMT before starting therapy, and more directed interpretative comments, such as advice on the most appropriate antibiotic(s) to use, may thus be indicated.

There is clearly a need for education of clinicians regarding indications for sending specimens and applying results to patient management. Susceptibilities can safely be withheld on non-critical microbiology reports. Combined with interpretative reporting, this promotes appropriate responses to such reports and discussion with the CMT, when therapeutic intervention is being considered. This approach is facilitated in our institution by a computerized reporting system, so that the time commitment from the CMT is not significantly increased. It allows us to affect the management of patients other than those who would routinely be seen on consultation. As such it forms an important part of the overall infection/antibiotic management programme in our institution.


    Notes
 
* Correspondence address. Department of Microbiology and Infectious Diseases, McMaster University Medical Centre, 1200 Main Street West, Hamilton, Ont. L8N 3Z5, Canada. Tel: +1-905-5212100; Fax: +1-905-5215099; E-mail: cunneyr{at}fhs.mcmaster.ca Back


    References
 Top
 Abstract
 Introduction
 Materials and methods
 Results and discussion
 References
 
1 . Brodowy, B. A., Guglielmo, B. J., York, M. K., Herfindal, E. T. & Brooks, G. F. (1989). Experience with selective reporting of susceptibility to antimicrobial agents. American Journal of Hospital Pharmacy 46, 1816–8.[ISI][Medline]

2 . Barnes, M. P. (1980). Influence of laboratory reports on prescribing of antimicrobials for urinary tract infection. Journal of Clinical Pathology 33, 481–3.[Abstract]

3 . Spencely, M., Parker, M. J., Dewar, R. A. D. & Miller, D. L. (1979). The clinical value of microbiological laboratory investigations. Journal of Infection 1, 23–36.[ISI]

4 . Ackerman, V. P., Pritchard, R. C., Obbink, D. J., Bradbury, R. & Lee, A. (1979). Consumer survey on microbiology reports. Lancet 313, 199–202.

5 . Doern, G. V., Vatour, R., Gaudet, M. & Levy, B. (1994). Clinical impact of rapid in vitro susceptibility testing and bacterial identification. Journal of Clinical Microbiology 32, 1757–62.[Abstract]

6 . Trenholme, G. M., Kaplan, R. L., Karakusis, P. H., Stine, T., Fuhrer, J., Landau, W. et al. (1989). Clinical impact of rapid identification and susceptibility testing of bacterial blood culture isolates. Journal of Clinical Microbiology 27, 1342–5.[ISI][Medline]

Received 27 April 1999; returned 9 August 1999; revised 18 October 1999; accepted 6 December 1999