The Finnish Study Group for Antimicrobial Resistance (FiRe), a network founded in 1991, has established a standard routine susceptibility testing method that yields reliable and comparable results for both diagnostic and epidemiological purposes. Results from FiRe show that the proportion of Streptococcus pneumoniae with resistance to macrolides is increasing and decreasing susceptibility of salmonella isolates to fluoroquinolones is being seen among isolates of foreign origin, but the prevalence of MRSA has remained low in Finland and multiresistant Mycobacterium tuberculosis is rare.

Each year in Finland, five million patients with infectious diseases are seen by doctors working in primary health care and hundreds of thousands of infectious disease patients are treated in hospitals. Over 200 000 bacterial isolates are tested for antimicrobial susceptibility in the 28 major clinical microbiology laboratories of the Finnish Study Group for Antimicrobial Resistance (FiRe) each year. FiRe, a network dedicated to research into the prevalence of resistance in bacteria isolated from humans, was founded in Finland in 1991.

During its first few years the main task for FiRe was to study antimicrobial resistance by sampling the bacteria that are clinically most important (1-4). Bacterial collection was centralised (isolates were sent to the reference laboratory for further studies) and the susceptibility tests were carried out using the same method, mainly the mean inhibitory concentration (MIC) plate dilution method. Because sampling studies are labour intensive, the next step was to standardise all bacterial susceptibility testing methods employed by the clinical microbiology laboratories.

One of the goals of FiRe, to establish a standard routine susceptibility testing method that yields reliable and comparable results for both diagnostic and epidemiological purposes, was achieved in 1996 (5-8). In principle, this method (FiRe Standard) is equivalent to the National Committee for Clinical Laboratory Standards (NCCLS) disk diffusion method. The interpretative breakpoints for susceptibility and resistance published by NCCLS are used with only a few exceptions and the breakpoints are updated each year. In addition to Mueller Hinton agar, Iso Sensitest agar (Oxoid) is accepted as the susceptibility medium by the FiRe standard method.

The comparability of the susceptibility test results is assessed by comparing the inhibition zone diameter distributions of patient strains and control bacterial strains from different laboratories. The results of such comparisons indicate good agreement between laboratories (unpublished data). The comparability of the results is in most cases good even between laboratories that use different culture media. In addition to these comparisons and routine external quality control programmes, the performance of the FiRe laboratories when testing for types of resistance that can be difficult to detect has been demonstrated by special surveys (5,7). For example, the detection of methicillin resistant Staphylococcus aureus (MRSA) in FiRe laboratories has been studied by three consecutive distributions of a set of S. aureus strains with different degrees of resistance to oxacillin. Susceptibility testing of Haemophilus influenzae is now under way. Such studies help us to recognise the positive and negative features of the FiRe standard and, if necessary and possible, to modify the standard further.

All of the Finnish clinical microbiology laboratories take part in the process of studying and developing the FiRe standard. Diagnostic laboratories provided the impulse for creating a common standard method. The problems and needs that arise in clinical laboratory work are discussed twice a year in meetings of the laboratory representatives, when points to be developed are also agreed.

Bacteria studied in 1998 by the FiRe laboratories showed no big problems in susceptibility, but some worrying developments were found. Firstly, the proportion of Streptococcus pneumoniae with resistance to macrolides is increasing (table). Should this trend continue, the treatment of pneumonia will become more difficult; macrolides are among the drugs recommended for the treatment of community acquired pneumonia. In addition, decreasing susceptibility of salmonella isolates to fluoroquinolones is being seen among isolates of foreign origin (9). We also have grounds for optimism, however, as the prevalence of MRSA has remained low in Finland and multiresistant Mycobacterium tuberculosis is rare. The complete summary of the resistance surveillance by the FiRe network has been published as a part of the FINRES 1999 report (www.mmm.fi/english/veterinary/publications/).

Table. Selected susceptibility test results from the FINRES 1999 report.

Bacterium

Antimicrobial agent

Year   (Nr of strains studied)   resistance %

Streptococcus pneumoniae

Penicillin (I+R)

1988-90

(639)

1,7%

1995

(807)

6,4%

1997

(6106)

4.8%

1998

(5245)

4.7%

Erythromycin

1988-90

0,6%

1995

2,7%

1997

5,3%

1998

6,9%

Haemophilus influenzae

1998

(4576)

Ampicillin

22,8%

Amoxicillin-clavulanic acid

0,5%

Sulphatrimethoprim

13,3%

Tetracyclines

1,7%

Neisseria gonorrhoeae

Ciprofloxacin

1998

(118)

5,1%

Escherichia coli (community urine isolates)

1998

(35113)

Ampicillin

30,3%

Mecillinam

5,9%

Cephalothin

7,3%

Norfloxacin

3,5%

Nitrofurantoin

3,2%

Trimethoprim

23,7%

Salmonella species (foreign isolates)

Ciprofloxacin (MIC 0,125 mg/ml or more)

1995

(100)

3,9%

1996

(200)

4,7%

1997

(100)

10,3%

1998

(100)

16,7%

Salmonella species (domestic isolates)

Ciprofloxacin (MIC 0,125 mg/ml or more)

1995

(100)

0,0%

1996

(200)

1,0%

1997

(100)

4,3%

1998

(100)

2,0%

Enterococcus faecium (hospital isolates)

1998

(1742)

Ampicillin

65,5%

Vancomycin

3,4%

Nitrofurantoin

2,6%

Methicillin resistant Staphylococcus aureus (MRSA)

Blood culture isolates

1997

(746)

0,5%

1998

(717)

0,7%

All isolates and one MRSA per patient

1997

(32 529)

0,4%

1998

(26 677)

0,7%

Mycobacterium tuberculosis

1998

(421)

Isoniazid

2,9%

Rifampicin

1,0%

Streptomycin

1,7%

Ethambutol

0,2%

Isoniazid+rifampicin

0,7%

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