Vancomycin resistance and avoparcin

Vancomycin resistance and avoparcin

Signing up for authorship SIR-Horton and Smith, in their Commentary on authorship (March 23),’ mention the 20% of survey respondents who felt that ...

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SIR-Horton and Smith, in their Commentary on authorship (March 23),’ mention the 20% of survey respondents who felt that they had been excluded from authorship despite deserving it. This is a feeling well known to radiologists and histopathologists. In histopathology the usual sequence of events is that a specimen arrives with minimum clinical information, but a rare and interesting diagnosis is apparent on histology. The diagnosis is received with scepticism and sometimes frank disbelief. Then, a few weeks later photos are solicited, after which there is silence. If a case report is eventually published it includes random phrases culled from the histology report-in one example (not from my hospital) an oesophagectomy and partial gastrectomy specimen was described as "irregular mucoid semi-translucent pale firm tissue weighing 280 g". The difficulty is most acute with papers published in small subspecialist clinical journals in which case reports are subject to little critical review. The simplest way to overcome this difficulty is to be generous with deserved authorship-in a case report that relies on histological diagnosis, the junior clinician who managed the patient and wrote up the case, their consultant if appropriate, and the pathologist who furnished the diagnosis, should be ample to avoid foolish mistakes, keep everyone happy, and avoid being relegated to "et al". The extent of head of the laboratory authorship is not so obvious now that Index Medicus is electronic. Previously a glance at the printed Index would reveal some authors so prolific that they filled nearly a page a year-at least a paper a

day.

D Simon C Rose Department of Histopathology, University College London Medical School, London WC1E 6JJ, UK

1

Horton R, Smith R.

Signing up for authorship. Lancet 1996;

347: 780.

Vancomycin resistance and avoparcin SIR As the manufacturer of avoparcin, a product which improves an animal’s digestion by controlling the growth of undesirable intestinal bacteria, we were interested in the comments of Howarth and Poulter (April 13, p 1047)’, and agree with them that the increase in vancomycin resistance is a potentially serious issue. However, to say that this increased resistance results from use of avoparcin is an oversimplification. A more useful exercise would be to investigate the role that human antibiotics, including vancomycin, have had in the development of antibiotic resistance in man. Howarth and Poulter refer to the Danish ban on use of avoparcin. However, the Danish report which led to the ban has been made available for peer review. Other European states have concluded that the Danish information does not justify a ban and, indeed, a recent British parliamentary answer from Angela Browning, Minister of Agriculture, Fisheries and Food, stated that "on the basis of currently available scientific information we do not believe that such a prohibition action is justified". This statement could not have been made without careful consultation with the drug licensing body the Veterinary Medicine Directorate. In addition, Prof Mark Casewell (University of London, King’s College Hospital), who is closely involved with organ transplantations, in a paper presented at the Pathological Society in January, 1996, concluded that vancomycinresistant enterococci from chickens are different strains from those obtained from patients in his hospital. This suggests

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that evidence for cross-resistance between animals and man is uncertain. Avoparcin has been used for the past 20 years, but vancomycin resistance in enterococci has only been noted quite recently and is associated with more extensive use of the drug to treat infections such as methicillin-resistant Staphylococcus aureus. It should be noted that vancomycinresistant enterococci have been recovered from livestock populations in which avoparcin has never been used, and they are well-recognised nosocomial infections. For the above reasons I believe that it is premature for your correspondents to suggest a suspension by the Veterinary Medicines Directorate (VMD) of the licence for avoparcin.

Anthony

Mudd

Roche Products Ltd, Heanor,

1 2

Derbyshire DE75 7SG, UK

Howarth F, Poulter D. Vancomycin resistance: time to ban avoparcin? Lancet 1996; 347: 1047. Hansard, 25 March, 1996; reply to written question number 69 column number 466.

Laboratory management of antibodies blood-group antigens in pregnancy

to

SiR-Clark’s Feb 24 commentary’ deserves rebuttal. He erroneously states that my colleagues* and I, as authors of practice guidelines for prenatal/perinatal serological testing,’ advocate monitoring antibody levels by measuring albumin agglutination titres. Nothing could be further from the truth. Such testing would be nonsensical since agglutinating antibodies tend to be IgM and, as such, do not cross the placental barrier to cause haemolytic disease of the newborn. Although albumin may promote direct agglutination of red blood cells by IgG antibodies, these antibodies are more readily detected by the indirect antiglobulin test. As we stated, our recommended method for antibody titres is an antiglobulin technique that uses anti-IgG and serial two-fold dilutions of patient’s serum, prepared either in saline or in 6% bovine albumin. Clark calls the use of a critical titre "conceptual rubbish". However, antibody titration-despite the inherent imprecision of the method-continues to be a practical approach to monitoring antibody levels in pregnancy. Titration studies are not used to predict the severity of haemolytic disease of the newborn but, rather, in the decision as to when to initiate change in optical density at 450 nm (AOD 45) analysis of amniotic fluid. The intent here is to limit the use of amniocentesis, which carries the risk of further stimulation of maternal antibody levels and therefore increased risk for severe haemolytic disease. Once a critical antibody level has been attained, serial LlOD45o values can be plotted, and decisions made whether or not to initiate further interventions such as cord blood sampling and periumbilical blood transfusions.3 There is evidence that titration studies are helpful in the decision making process, especially in the first affected pregnancy.4 A low but rising titre or a history of previously affected pregnancies should also be taken into account when assessing the need for amniotic fluid analysis. Observations by high-resolution ultrasound may further influence the decision to undertake invasive procedures. Clark bases his attack on the concept of the critical titre in recent European publications that promote use of macrophage chemiluminescence or antibody-dependent, cell-mediated cytotoxicity assays. Such tests may be better than a simple what cost? In

antibody titration, but by how much and at Europe, prenatal serological testing is usually managed by regional blood donor centres, which have the expertise to do such assays. By contrast, prenatal testing in