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Suggestions for the most appropriate format of features for diagnosing atopic eczema in various study scenarios are given below. Before these are discussed, it is important for the researcher to appreciate one further point which might influence the way in which the data is recorded and coded. It would be naive to expect that the preferred format of itch plus three or more features could not be replaced by better criteria in the light of future discoveries on disease aetiology. Whatever new disease definitions emerge, the separate elements which make up the UK diagnostic criteria (eg history of flexural itchy rash) are still likely to useful in describing AE phenotype in future studies, especially for investigating secular trends and international comparative prevalence estimates. For this reason, in addition to composite measures such as atopic eczema "yes/no", we strongly recommend that the subjects' responses to individual criteria are retained separately on file. It might also be useful to record self-reported and doctor diagnosed "eczema" or "atopic dermatitis" in some surveys so that the effects of disease labelling can be explored.
We suggest itch plus three of more of the features shown in Table 1. It will be noted that since the presence of an itchy skin condition is the sole necessary criterion, then only subjects responding affirmatively to this question need to be examined further for evidence of visible flexural dermatitis. Such a strategy might save considerable expense and time, although some researchers may also wish to examine a sample of those without a history of an itchy rash to assess the proportion of false negatives.
If examining individuals is out of the question, then the questions only version (itch plus two or more out of the remaining four features in Table 1) should be used.
For countries where the prevalence of AE is anticipated to be very low (ie under 4%), or for areas where other skin diseases such as scabies which could easily be confused with AE are very common, please read Section 5.
Again, itch plus three of more criteria. It will be possible to model the potential effects of misclassification as outlined in Section 5.
The AE criteria have not caused any difficulties in studies surveying all three major allergic diseases to date. One of the six criteria for diagnosing AE is a personal history of hay fever or asthma. It is possible that the inclusion of asthma/hay fever within the definition of AE may be undesirable in some surveys which wish to keep the elements of the three allergic diseases entirely separate. If the inclusion of asthma/hay fever as part of the diagnosis of AE is unacceptable to an investigator, we recommend that AE should be defined in terms of single unambiguous items such as history of flexural itchy rash or visible flexural dermatitis. If it is deemed acceptable to use history of asthma/hay fever as part of the definition of AE, then in order to reduce variability, it might be prudent to substitute self-report of asthma and hay fever by more objective means if these are available within the survey.
Since only a fraction of cases are sampled in most case-control studies, more specific, less sensitive criteria formats such as itch plus four or more features might be more suitable to minimise inclusion of false positive cases. Care has to be taken in selecting controls for nested case-control studies however to avoid selecting possible cases (eg those with itch plus three features). In such nested case-control studies, controls should be selected from all those with who have replied negatively to an itchy skin condition.
Measurement of disease incidence poses difficulties as AE is usually an intermittent disease. The criteria proposed in this manual all refer to prevalent cases. In a cohort study, it might be appropriate to use the one year period prevalences as a measure of disease incidence if they are recorded annually. Alternatively, incident case of AE could be defined as any person who develops an itchy skin condition for the first time which is also compatible with AE (ie visible flexural dermatitis with modifications for young infants as outlined in the protocol). It is also possible to use the criteria to measure lifetime prevalence of AE by using "Has your child ever had an itchy skin condition?" for question 1 of the questionnaire shown in Appendix 1. Although this is not strictly the same as cumulative incidence since disease ascertainment has not been recorded prospectively, it may serve as a useful approximation.
There is no reason why the preferred criteria format of itchy skin plus three or more features could not be used in hospital studies which seek to recruit a representative population of AE cases. This would also permit the selection of cases who are not necessarily active at the time of recruitment, and this might reduce the tendency to record epiphenomena associated with disease activity/severity as has been the case in some previous hospital studies of AE subjects.
These would probably require subjects to have active disease on entry into a trial. Because cases referred to hospital are usually quite severe, it is likely that all hospital ascertained cases of AE will have active dermatitis, and the normal criteria format of itch plus three or more features could be used. For clinical trials which employ community ascertained cases of AE, it is possible that cases so defined will not have active dermatitis at the time of recruitment. Cases could then be restricted to those with current active disease if this is a trial requirement.
Some laboratory based studies might require a stricter definition of the use of the word "atopy" when defining subjects with atopic eczema. In such a context, atopy as defined by a positive skin prick test reaction (or raised allergen specific IgE) to one or more common environmental allergens could be included as an additional necessary criterion for all cases.
Studies which seek to estimate the disability or costs of AE in the community need to ensure that they include all possible cases, and that all those included have definite AE. A serial strategy of a sensitive screening question such as itchy rash in the last 12 months followed by a skin examination and other questions included in the UK criteria might be useful here. If prevalence is the main objective of the survey, then itch plus three or more criteria should be used. If the main aim of the survey is to document the detailed morbidity/costs associated with a representative sample of AE cases, then cases could be defined by highly specific definitions such as itch plus four or more features.
Although the UK refinement of Hanifin and Rajka's criteria were primarily designed for use in population surveys, they may be useful to family practitioners who wish to describe groups of subjects for audit studies. They may also be useful as a diagnostic aid to those less familiar with AE, but care must be taken in not interpreting failure to fulfil the diagnostic criteria as proof of excluding AE as apposed to the correct interpretation that AE is not probable within a certain degree of confidence at that moment.