Standardization of serological reagents

Will the dilemma of evidence-based surgery ever be resolved?

Exponents of evidence-based medicine do not undermine the importance of clinical expertise and skills, but they emphasize that decision-making in medicine should be based on the best available evidence derived from the systematic analysis of observations made in an objective, unbiased and a reproducible fashion. The randomized controlled trial (RCT) is the most scientifically rigorous means of hypothesis testing in epidemiology. Discrepancies between established surgical and other interventions and best available evidence are common. These can be in the form of significant delay in adopting a new intervention despite strong supportive evidence, adopting an intervention before supportive evidence becomes available for reasons of novelty or pear pressure and the lack of supportive evidence for many established common practices. This is compounded further by the paucity of good quality evidence for most surgical procedures. This is arguably because of the inherent difficulties in conducting surgical RCT. The practical, ethical and financial ramifications are complex and the nature of surgical disease often compromise the chances of success or completion of RCT. Carrying out surgical RCT may have more implications on the clinician's authority, autonomy and income and their results are more likely to be influenced by his/her expertise and competence than medical RCT. Furthermore, the success of surgical RCT is often jeopardized by very low recruitment rates. The aim of this study is to discuss the dilemma of producing evidence in surgery.

The properties of different Salmonella Vi antigens

The labile Vi antigens ofSalmonella typhi, Salm. paratyphi AandB, and ofSalm. typhi-muriumwere compared, especially in their response to various chemical and physical agents.

1. Inactivation by dilute acid:

(a) The TVi antigen is the most resistant to acid treatment, the BVi antigen is most readily inactivated and the AVi antigen holds an intermediate position.

(b) Pure Vi sera may be obtained by absorption with acid-treated bacilli, but this technique gives irregular results.

(c) Contrary to Kauffmann's statements, the TVi antigen is not ‘destroyed’ by acid treatment.

2. Inactivation by dilute alkali:

(a) All the Vi antigens so far tested are susceptible to dilute alkali.

(b) Complete inactivation, or extraction, of the Vi antigens is ensured when the yield of alkali-treated bacteria represents no more than 25% of the original bacterial count.

(c) The most reliable method of preparing a pure Vi serum is by absorption of the Vi + O serum with alkali-treated organisms of the same strain as that employed in immunization.

(d) Immunization with alkali-treated bacilli results in the elaboration of pure 0 antisera entirely devoid of Vi antibody.

3. Inactivation by heat (in aqueous suspensions):

(a) The TVi antigen is the one most readily inactivated, the BVi antigen is the one most resistant and the AVi antigen holds an intermediate position.

(b) These differences are only of minor significance, since similar differences have been established for the TVi antigen itself when it is contained in the two varieties of Vi strain of Salm. typhi.

4. Treatment with alcohol:

(a) Most of the properties of the threeSalmonellaVi antigens remain unimpaired by alcohol treatment.

(b) The physico-chemical behaviour of alcohol-treated or heated bacilli, as exemplified by agglutinability by pure Vi antiserum, depends on the presence of other constituents of the bacterial cell.

5. Treatment with formalin:

(a) The Vi agglutinability of the differentSalmonellais preserved undamaged for long periods of time. The 0 inagglutinability ofSalm. typhiis also well maintained.

(b) It is not yet known whether formolized AVi and BVi antigens undergo an alteration that leads to ‘functional deficiency’ of the corresponding antibody similar to that of the altered T Vi antibody.

6. Treatment with phenol produces a reversible inactivation of the agglutinogenic activity of the T Vi antigen but not of the A Vi and B Vi antigens.

7. The inadequacy of the symbols employed by Kauffmann for expressing the changed reactivity of differently treated antigens is emphasized.