Case Studies:EpidemiologyHow common is atopic eczema?Much of the published work on the epidemiology of atopic eczema has been done in children (Diepgen T 2000) and a variety of prevalence measures have been used which include lifetime prevalence, point prevalence and 1-year prevalence rates. The ISSAC studies (Williams H et al 1999; Asher MI et al 2006) have documented that the 1-year prevalence rate varies worldwide dependant on the population and geographic area studied (globally, nationally or locally). A comparison of the two studies documents a decline or plateau 1-year prevalence rate in the developed world but an increasing prevalence in the developing world. While it is accepted that atopic eczema is a particular problem in children, the burden of disease is significant in adults. A study in adults in Scotland document a 0,2% 1-year point prevalence for atopic eczema in those over 40-years of age. Adults accounted for 38% of the atopic eczema population (Herd RM et al 1996) Few incidence studies have been done and these are in cohorts of children (Halkjaer LB et al 2006). There are no studies addressing the prevalence of atopic eczema in South African adults. The Phase I ISSAC study (Williams H et al 1999) of 13 to 14 year old school children in Cape Town showed a 8.3% 1-year prevalence rate with 2,3% having severe disease. The Phase III follow-up study (Asher MI et al 2006) documented an increased 1-year prevalence of 13.3% amongst children of the same age. In 3 to 11 year old normal children the 1-year prevalence rate was 1 to 2.5% in Xhosa children dependant on the methodology used to define atopic eczema (Chalmers DA et al 2007). What is the natural history of atopic eczema? Studies on the natural history of atopic eczema document up to 60% spontaneous clearing by puberty (Williams HC et al 2000; Illi S et al 2004; Halkjaer et al LB 2006). Studies on adults are rare but suggest that early adult atopic eczema is associated with persistent disease in later life. Atopic eczema may recur in adults and the risk is associated with the severity and persistence of childhood atopic eczema. In adults the clinical picture may be altered, patients presenting with hand eczema caused by exposure to additional insults such as irritant like wet work, detergents, chemicals and solvents or head and neck involvement (Sandstrom Falk MH et al 2006). The historical concept of the “atopic march”, where children with atopic eczema would evolve into mucosal forms of atopic disease has been challenged by co-hort studies (Williams HC et al 2006, Flohr C et al 2004). Early wheeze and specific sensitisation pattern (wheat, cat, mite, soy, birch) were predictors of wheezing at school age irrespective of the presence of atopic eczema in a German birth co-hort study (Illi S et al 2004). The development of rhinoconjunctivitis is more strongly associated with atopic eczema than is asthma. It is probable that there are many subset of the atopic eczema phenotype. Studies assessing the severity of atopic eczema in Europe revealed that in children, 84% have mild, 14% moderate and 2% severe disease (Emerson RM et al 1998; Dotterud LK et al 1995). In adult cohorts, those that had severe disease accounted for 12% using the SCORAD scoring system (Sandstrom K et al 2006). |
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