Epidemiology of cystic fibrosis: a review.

Three main reasons have been advanced for the degree of ignorance and 
confusion surrounding epidemiologic measures of the incidence and prevalence of Cystic 
Fibrosis. (CF) Relatively recent recognition of CF as a specific disease 
entity. Wide range of clinical manifestations, presentation as a multisystem disease, 
and great natural variation in the severity of involvement of various 
organs. Past difficulty in establishing a diagnosis based on sound laboratory 
evidence, this being largely due to the lack of a screening 
test that had gained wide acceptance among diagnosticians, and inaccuracies in 
the performance and interpretation of the sweat test. In addition to 
these factors, there are a number of methodological deficiencies and questionable 
assumptions in several of the papers that have here been reviewed. 
It may be noteworthy that the two sets of authors whose 
research design most closely matched being aimed at providing multiple ascertainment 
of cases and cross-checks of validity, have arrived at nearly the 
same estimated incidence of this particular disorder (1/3700 and 1/3800 respectively). 
The issue of selection and diagnostic criteria is one that has 
important implications for epidemiologic studies of cystic fibrosis. Particularly in a 
disease like CF, where the spectrum of clinical manifestations and severity 
of involvement is so broad, estimates of incidence will vary according 
to the criteria by which cases are ascertained and included. A 
greater degree of uniformity in standards than has been employed in 
previous studies is necessary before comparisons can meaningfully be made. There 
are good grounds for regarding most estimates of CF incidence to 
be minimum confirmed figures, and this is particularly so where the 
research design ensures that multiple ascertainments of the same case will 
be identifiable. Higher estimates are made where several sources of error 
(respondent bias, generalization of hospital data to the wider population, multiple 
ascertainments of the same patient) are not recognised. 