HOW CAN THE DIAGNOSTIC LABORATORY HELP?

5. HOW CAN THE DIAGNOSTIC LABORATORY HELP?

The issues are several fold, including access to the laboratory, speed and accuracy of analysis, and communications of results. It is fashionable to emphasise the importance of molecular diagnostics in this context, particularly in view of the speed of these tests and there is no doubt that rapid results can improve patient outcome and quality of antibiotic use. Nevertheless, molecular tests have not, so far, become well integrated into clinical diagnostic micro- biology and the near future does not hold a great deal of promise.

In fact, much more can be done using conventional technology both in the community and hospital. Ease of access with same day delivery and process- ing may seem a luxury, at least in primary care, but has been shown to be feasible and reduce antibiotic prescribing by at least 50% (Shackley et al., 1997) (Figure 3). Even with conventional tests, most specimens in primary and secondary care can yield useful preliminary results after overnight incubation.

Antibiotic Use—Ecological Issues and Actions 711

Figure 3. Accelerated Bacteriology Laboratory Evaluation for better quality antibiotic pre- scribing in general practice and in hospitals.

Source: JAC (1997: 39, 663–666).

712 Ian M. Gould In primary care most patients can wait overnight for results to see if an antibi-

otic is indicated. Results can be communicated electronically, or by fax, to the GP and the patient can then telephone the surgery to see whether, or not, to activate a delayed prescription. For emergency specimens in hospitals, gram stains and antigen tests should be available within minutes. The rate limiting step is transport of the specimens to the laboratory. Ninety per cent of positive blood cultures will be positive within 24 hr (MacKenzie et al., 2003) and these and all intensive care specimen results should be telephoned to the duty doctor, or better still, the patients visited by a medical microbiologist to ensure appro- priate (often streamlined) therapy. In particular, appropriate therapy can be started if the empiric choice is inactive, or a broad-spectrum, empiric choice can be downgraded based on real or anticipated susceptibilities of the isolate (Figure 2). Clinicians need much more education on the issues of streamlining and step down as their natural inclination is to ignore negative laboratory results and keep the patient on the original empiric choice if they are doing well (Cunney and Smyth, 2000).

In my own hospital, one of the most common reasons for an inadequate choice of empiric antibiotic therapy is MRSA bacteriaemia when the patient has been given a quinolone or third generation cephalosporin. If MRSA is a problem in an institution, then empiric therapy should take account of this. In my own hospital all our MRSA are susceptible to gentamicin so this agent plus a broad- spectrum penicillin is recommended as empiric therapy for life-threatening sepsis. A crucial role of the laboratory is to analyse its historical data by origin of specimen to inform the local antibiotic policy about the best options for empiric therapy. Computer programmes are now available for such purposes, based on time-series analysis of previous year’s data (www. viresist.org/).

Quality control in the laboratory is, of course, essential and probably the best scheme in Europe is run by UKNEQAS (www.ukneqas.org.uk/). It now offers

24 cultures per year, specifically designed to highlight problems with detection of antibiotic resistances of clinical relevance. Current challenges for labs are detection of ESBLs, carbapenemases, glycopeptide intermediate staphylococci, and the general issue of susceptibility of non-fermenting Gram-negative rods which really have to be tested by MIC methodology. Standardisation of labora- tory methods for susceptibility testing is another topical issue, predominantly so that results can be used for surveillance and EUCAST is making great strides forward on a European platform (www.escmid.org).