Interaction between the microbiology laboratory and clinician: what the microbiologist can provide

The work of the clinical microbiologist comprises three major areas: diagnostic work in the laboratory, advice to clinicians about treatment of infected patients, and infection control. By clinical alertness, either from work in the laboratory or from clinical contacts, the microbiologist may contribute to the recognition of hospital outbreaks. The microbiologist plays a key role in implementing a restrictive antibiotic policy in hospital. Experience shows that a close personal contact with clinicians in the daily treatment of patients is the most efficient way to ensure a rational use of antibiotics and keep the consumption low. Other important measures include the elaboration of antibiotic guidelines and performance of audits. On basis of periodic summaries of laboratory data and data on antibiotic consumption, the microbiologist can keep the clinicians informed about antibiotic resistance and compliance with the antibiotic guidelines. In addition to informal contacts, the microbiologist also interacts with clinicians through participation in infection control and drug and therapeutic committees.

[National surveillance of Helicobacter pylori eradication in Denmark. Results based on registration of 34.582 drug prescriptions]

We wanted to characterize the use of H. pylori eradication therapy in Denmark (inhabitants 5,227,862). All H. pylori eradication treatments from a nation wide database covering all drug prescriptions in the period January 1994-June 1996 were identified. We found 28,784 out-patients having a prescription with drugs for H. pylori eradication, accounting for 34,582 prescriptions in total. The incidence of new consumers was 220 per 10(5) inhabitants per year, with a maximum at 70-79 years of age. Eighty-six percent of the patients had only one treatment course. Forty-five percent had an anti-ulcer drug prescribed 1-12 months after the H. pylori eradication therapy. Consumption of antibiotics used for H. pylori eradication accounted for 1.4% of the total consumption of antibiotics. In conclusion, the incidence of H. pylori eradication therapy was fairly stable but with changes in the pattern of drug regimens used. Anti-ulcer drugs were often given after H. pylori eradication therapy, suggesting an inappropriate use of eradication treatment.

[Infections and cardiovascular disease]

Epidemiological studies indicate that respiratory tract and dental infections increase the risk of atherosclerotic cardiovascular disease. Several microorganisms have been claimed as clinically important, especially Chlamydia pneumoniae (Cp) and cytomegalovirus (CMV), Cp is frequently isolated from atherosclerotic plaques, and treatment with macrolide antibiotics may have a beneficial effect on the course of ischaemic heart disease. CMV seems to play a role in the development of coronary stenosis following coronary bypass surgery and heart transplantation. Likewise, inflammatory markers are associated with atherosclerotic cardiovascular disease. The pathogenetic role of microorganisms may be ascribed to the inflammatory response, which is elicited during infection. There is an urgent need for more documentation of the role of microorganisms in cardiovascular disease, and of the possible clinical effect of antibiotic treatment.

Resistance problems in two university hospitals in Denmark

In 1997, 80 and 89% of Staphylococcus aureus isolated from university hospitals in Odense and Hvidovre respectively were resistant to penicillin and 32.0 and 41% of Escherichia coli were resistant to ampicillin. There were low incidences of methicillin resistance in S. aureus (<1%), penicillin resistance in Streptococcus pneumoniae (3%),and gentamicin in E. coli (2%). These figures might reflect the low use of antibiotics in Denmark.

Poor value of surveillance cultures for prediction of septicaemia caused by coagulase-negative staphylococci in patients undergoing haemodialysis with central venous catheters

Surveillance cultures for the demonstration of coagulase-negative staphylococci in patients on catheter haemodialysis were performed in an attempt to predict dialysis catheter-related septicaemia. In all, 43 patients with 67 haemodialysis catheters were followed for a 1-y period. Once a week, swab specimens were obtained from the skin at the insertion site and the hub, and blood cultures were obtained from the catheter. Among coagulase-negative staphylococci, S. epidermidis was the most frequently (80%) isolated species, and two biotypes accounted for 55.7% of the 41 biotypes isolated. 11 septicaemia cases due to coagulase-negative staphylococci occurred, all caused by S. epidermidis, and the incidence of S. epidermidis septicaemia was 21% among patients and 16% among catheter periods. S. epidermidis septicaemia occurred in 17%, 31% and 33% of all catheter periods in which S. epidermidis was cultured from the skin, hub and catheter blood, respectively. In two-thirds of all catheter periods, S. epidermidis was cultured from catheter blood despite lack of clinical signs of septicaemia. In conclusion, cultures from the skin, hub or catheter blood are not useful for prediction of dialysis catheter-related septicaemia due to coagulase-negative staphylococci. When septicaemia is suspected, peripheral blood cultures are mandatory to reach a correct diagnosis and aetiology.

[Carriers of Staphylococcus aureus as a source of nosocomial infections. Epidemiological and prophylactic aspects]

20% of the normal population are nasal carriers of Staphylococcus aureus (Sa), and the carrier rate is even higher in insulin dependent diabetics, intravenous drug addicts, patients on haemo- and peritoneal dialysis, and HIV infected patients. Nasal Sa carriers have an increased risk of Sa infections following invasive therapy. Mupirocin, a novel topical antibiotic, is highly effective against nasal Sa. A number of studies indicate that it may reduce the incidence of Sa infections in dialysis patients, however experience with other categories of patients is sparse. Surgical wound infection with Sa is a particularly serious complication after implantation of foreign body material, e.g. artificial joints. There is a need for controlled clinical trials to test the efficacy of mupirocin in eradicating Sa in these types of patients. Uncritical use of mupirocin for topical treatment of wounds should be avoided in order to prevent development of resistance.

Dialysis catheter-related septicaemia--focus on Staphylococcus aureus septicaemia

BACKGROUND

Dialysis catheters are a common cause of nosocomial septicaemia in haemodialysis units usually due to staphylococci, of which Staphylococcus aureus is the most pathogenic. In this study, the epidemiology and pathogenesis of dialysis catheter-related infections were studied, and methods to identify patients with these infections were evaluated.

METHODS

A one-year prospective study of 67 catheters in 43 haemodialysis patients was performed. Details about patients and catheters were obtained successively during the catheter period, and biochemical parameters expected to be related to infection were measured. After catheter insertion, all patients were screened for nasal carriage of S. aureus, and a culture was taken from the skin overlying the catheter insertion site. Once a week, cultures were taken from the insertion site and from the hub, and aerobic and anaerobic blood cultures were drawn from the catheter. If clinical signs of septicaemia occurred, peripheral blood cultures were also performed, when it was possible.

RESULTS

The incidence of septicaemia was 49% (21/43) in patients, and 56% of all cases were caused by S. aureus. The mortality was 14% (3/21) and the incidence of severe secondary complications to septicaemia was 24% (5/31). In all, 80% of all severe complications and 75% of all deaths from septicaemia were due to S. aureus. With respect to S. aureus septicaemia, the predictive values of positive (P) and negative (N) S. aureus cultures were as follows: nasal culture, P=36% (10/28), N=90% (35/39); culture from the insertion site, P=72% (13/18), N=98% (48/49); and culture from the hub, P=75% (3/4), N=83% (52/63). The risk ratio for S. aureus septicaemia was 26.2 (6.1-113), P=0.0001, according to the presence of S. aureus at the insertion site, and 3.3 (0.74-15.1), P=0.12 according to nasal carriage of S. aureus. The frequency of S. aureus phage-type Group 2 (43%) was much higher than the general frequency of this phage-type in Denmark, which is about 23%. Catheter blood cultures were positive although there were no clinical signs of septicaemia in 34% (23/67) of all catheter periods--84% of these were due to coagulase-negative staphylococci.

CONCLUSIONS

Dialysis catheter-related S. aureus septicaemia was highly unlikely if the patient had not been carrying S. aureus in the nose or at the insertion site during the time the catheter was in place. The best predictor of dialysis catheter-related S. aureus septicaemia was a positive S. aureus culture from the insertion site. Positive catheter blood cultures unrelated to any clinical signs of septicaemia occurred in one-third of all catheter periods, and 84% of these were due to coagulase-negative staphylococci.