Bovine TB: 3 Questionnaire-based Epidemiological Survey (TB99)
- 3.1 The development of TB99
- 3.2 Application of the questionnaire
- 3.3 Reviewing Progress
- 3.4 Complementary studies
3.0.1 It is our view that an objective and comprehensive assessment of the factors which predispose herds to a TB breakdown and their relative importance can best be achieved by surveying a large number of cattle farms using a structured questionnaire to collect carefully specified data which are then subjected to appropriate analysis. We have considered the value of other approaches (for example, on-farm experiments) to provide useful complementary data but have dismissed them at this stage since risk factors and their contributions remain so uncertain, and because of the difficulty of controlling the many possible variables involved.
3.1 The development of TB99
3.1.1 For many years MAFF has collected information from all farms experiencing a TB breakdown, using a structured form referred to as TB49. This was designed solely to aid incident management and not to gather epidemiological data. However, the form attracted criticism because it was used in an attempt to ascribe the cause of the TB outbreak, based on a subjective assessment.
3.1.2 Professor Krebs proposed that the TB49 form be re-designed. We strongly endorsed this recommendation, and a working group was established at the outset to develop a questionnaire which would secure data on a range of potential risk factors. In parallel, a research assistant was appointed to work with the Veterinary Laboratories Agency on the design of a database to manage the information to be collected.
3.1.3 In designing the new questionnaire, designated TB99, the working group was guided by a number of key, although sometimes competing, principles:
- the need for objectivity
- the need to be comprehensive
- the need to provide data amenable to statistical analysis
- the need for practicability.
3.1.4 Applying these principles required extensive consultation with research workers in various fields, farming and conservation interests, and others in this country and overseas. Designing a questionnaire that was sufficiently comprehensive but which was amenable to analysis and would not over-burden farmers proved challenging. As part of the development process, MAFF staff piloted a draft version of TB99 on-farm at the end of 1998. In parallel MAFF consulted publicly on the version being piloted. Both actions proved extremely valuable and the feedback was largely positive. The working group took full account of the pilot exercise and of the views of respondents to the consultation in further refining the questionnaire. MAFF has implemented a national training programme for staff administering the final form to maximise objectivity.
3.1.5 On each farm to which it is applied TB99 collects data on a wide range of potential risks factors relating to the 12 month period prior to the herd breakdown. These include cattle herd composition and health, cattle movements, the type of farm enterprise (including land type/use, soil type, presence of other domestic species), husbandry factors (such as grazing practices, fertiliser use, effluent management, water sources, housing/bedding arrangements, supplementary feeding practices, steps taken to avoid contact between cattle and wildlife) and the presence of potential wildlife sources of TB infection. These data will be analysed to identify and rank the factors which, individually and in combination, appear to predispose farms to TB breakdowns (see Section 8.1).
3.1.6 TB99 was seen by some as too detailed, and by others, as too limited in scope. We feel that, at this stage, we have got the balance about right. TB99 meets the key objective of scanning as wide as practicable and reasonable a range of factors which could influence TB in cattle. Failure to meet this requirement would have risked missing key factors by prejudging their relevance. At the same time, because of the need to be concise and user-friendly, the Group accepts that more detailed studies may be necessary in the future if the analyses of TB99 identifies factors that show significant associations with risk of TB in cattle.
3.2 Application of the questionnaire
3.2.1 TB99 was formally launched by MAFF in April 1999, following a brief second pilot phase. The questionnaire is completed by trained MAFF State Veterinary Service staff through one or more personal interviews with the farmers concerned. At the time of going to press over 500 questionnaires had been completed.
3.2.2. The questionnaire is now being used on all farms in Great Britain (within and outside trial areas) on which a confirmed TB breakdown occurs and is also being applied retrospectively to all breakdowns which occurred since the beginning of 1999. In trial areas, every breakdown (whether confirmed or not) triggers a TB99 survey. There are two slightly different versions of the TB99 questionnaire. One, ‘the case form’, is used on the breakdown farm. In addition, in trial areas, for each such breakdown a ‘control form’ is applied to each of three comparable herds (including, where possible, one contiguous herd) from within the same trial area. The control form collects information on comparable farms (over a comparable time-period) where no outbreak has occurred and is identical to the ‘case’ form except that it omits questions included for incident management purposes. On-line proof copies of both the case and control forms are available on MAFF’s TB Website (www.maff.gov.uk/tb/krebs/c9_pdf.htm). The selection of control farms has been limited to trial areas because, at this time, these are the only areas for which detailed badger epidemiological data will be available.
3.2.3 We are grateful to all those farmers who have given valuable time and provided detailed information to help us with this work. Our thanks go also to the State Veterinary Service staff who have been involved in administering the form, and have provided essential feedback.
3.3 Reviewing progress
3.3.1 The Group recognises that the questionnaire is a substantial document and understands concern about its complexity. Given its importance to our objectives, we plan to subject TB99 to a thorough review programme, both in the field and as data are audited and entered into the database, and, with MAFF, to continue to monitor the implementation of the new form. Reports from MAFF on the early experiences suggest the questionnaire has been generally well received. Preliminary analysis will help evaluate the robustness of data and identify changes which could improve its quality and coverage.
3.4 Complementary studies
3.4.1 TB99 is being complemented by other studies into possible risk factors. The Veterinary Laboratories Agency, the Royal Veterinary College and the Universities of Cambridge and Warwick are each undertaking their own multifactorial analyses of TB data.
3.4.2 The Group has considered the case for complementing TB99 with the introduction of an additional ‘five year’ questionnaire (either as a stand-alone questionnaire or as an adjunct to TB99). The proposed five year questionnaire was to be applied on a sample of farms located in trial areas with a view to analysing the differences between management practices on those farms in the previous 12 months compared with a similar 12 month period five years earlier and, where significant differences were detected, assessing whether these could be associated with an increase or reduction in the risk of a TB outbreak. However, after careful thought we have concluded that the resource implications involved in obtaining a sufficiently large sized sample, taken together with concerns about the reliability of historical data, outweighed the potential benefits. We are nevertheless considering further the desirability and viability of a straightforward questionnaire which would be completed by farmers on enrolment into the trial, so that potentially valuable data are not lost.
On to Chapter 4 - The Field Trial 
Page last modified:
12 August 2003
Page published: 5 February 2003