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The place of epidemiology in the study of rheumatoid disease.

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EDITORIAL
The Place of Epidemiology in the Study of
Rheumatoid Disease
T
HE METHODS of epidemiology are appropriately looked on as at the
extreme, opposite end of the methodologic scale from those of biochemistry and biophysics, for epidemiology deals with disease at the population
level rather than the individual, cellular, or molecular level. In general,
epiclcmiology may be said to have three important functions. The first is to
extend the understanding of the severity gradient by studying those persons
who have the disease in a form too mild to cause them to seek medical treatment. In the second place, it can provide direct information about the extent
of the problem of any particular disease and about variations in the extent of
this problem with respect to time and space. In the third place, studies of
populations can provide useful information about association between various
factors of interest and the presence or absence of a particular disease.
With these thoughts in mind, let us take a brief look at the contributions
that epidemiology has made in recent years to our understanding of rheumatoid disease. There seem to be three ways in which field studies have contribllted to our understanding of its gradient of severity. The first of these is
the renewed interest in morning stiffness as a unifying factor in rheumatoid
disease. The importance of this has been emphasized in the reports of the
Pittsburgh Arthritis Study. The second contribution to our knowledge of the
yraclient comes from the recognition of cases of rheumatoid disease without
arthritis. We have now seen rheumatoid nodules without arthritis, or rather
preceding the development of arthritis, x-ray evidence of rheumatoid arthritis
vreceding any joint complaints, and serologic tests positive in patients with
arteritis without arthritis. The third contribution in this area is best expressed
hy the attitude of Kellgren' and his colleagues in England that the sheep cell
test is an indication of rheumatoid arthritis or of susceptibility thereto. This
last concept brings a new tool to the study of the familial aspects of this
disease, for it was recently reported by Lawrence1 and by Ziff' that the
serologic tests are much more commonly positive among the siblings of
patients with rheumatoid arthritis than they are in the general population.
This matter is clearly of great potential importance and deserves further seri011s attention.
In terms of estimates of incidence and prevalence, we can only say that to
date we haveno adequate estimates of the total incidence of the disease though
we do have some estimates of the incidence of disease severe enough to cause
the individual to seek medical attention. With regard to prevalence, on the
other hand, considerable progress has been made in our ability to make comparisons in time and space as a result of the acceptance of the American
Rheumatism Association Criteria.2 Doubtless, all of us have some reservations
abont the absolute validity of these criteria; however, few would dispute the
fact that the existence of these criteria markedly reduces inter-observer variation in the diagnosis of this disease. The first step towards establishing a
geographv of rheumatoid disease w a s accomplished with the piblication of
253
254
EDITORIAL
a report on the difference in prevalence between Pittsburgh, Pennsylvania
and Manchester, Englande3
Up until quite recently, the tools have hardly been available for the thirdmentioned aspect of epidemiologic work, namely, the study of the association
between rheumatoid arthritis and assorted host and environmental factors. AS
a result, most of the studies that have been done are based on full clinical
examination of samples of individuals. From studies of this sort have come
some indications that marital status is of importance in regard to this disease,
evidence that infections may be associated with onset, and a partial clarification of the relationship between rheumatoid arthritis and osteoarthritis. In
general, however, it is felt that this method is much too laborious for widespread application. For studies of this sort there seem to be three possible
methods for circumventing the difficulties of full clinical examination. The
simplest, and least expensive, though perhaps conceptually the most difficult
to accept, is the technic proposed by Rubin and his collaborator^.^ This
technic involves the use of a set of questions asked by a non-medical interviewer. The answers to these questions constitute an index of rheumatoid
arthritis of sufficient sensitivity and specificity to give useful results when
samples of sufficient size are interviewed, and as long as there is reason to
believe that the index has the same validity among persons with the characteristic under study as among persons without the characteristic in question. A
practical demonstration of the usefulness of this method is found in the report
of King on Psychosocial Factors in the Epidemiology of Rheumatoid Arthritis5
The second way to circumvent our difficulty is through the use of serologic
surveys of the kind already done by Feldman in Syracuse. Serologic surveys
tend, unfortunately, to be *moresubject to non-response errors because there
are a reasonable number of people in the general population who are unwilling
to give a blood sample. The technic is, however, extremely useful.
The third possibility is the development of a screening device of sufficient
sensitivitv which can be applied to people in their homes or at their places
of work bv nurses, medical students, or even possibly by entirely non-medical
persons. Those who screen positive are then referred for detailed examination,
serologic tests and x-ray examination in a clinic. This clearly cuts the expense
of examining everybody and reduces to a minimum the non-response error
because, by and large, those who are found to have some evidence of arthritis
on a screening examination are willing to have it further investigated in the
clinical situation, and this type of interview is usually well accepted. A technic
of this sort is now being tried in the Pittsburgh Arthritis Study and the screen
currently in use shows great promise.
With the field methodology for epidemiologic study of this disease developing SO rapidly, and analytic methods advancing also,l it now seems highly
probable that this investigative discipline will take its place along side of, and
share the honors with, the laboratory and the clinic in the years to come. The
field is wide open, for there are very few physicians interested in this approach.
The basic training required for this kind of work is usually obtained in schools
255
EDITORIAL
of public health. At some of these schools substantial fellowships are available
to individuals seeking training in the epidemiology of this and other noncommunicable diseases.
SIDNEYCOBB,M.D., M.P.H.
REFERENCES
1. Kellgren, J. H., Ed.: Transactions of the
First International Conference on Population Studies in Rheumatoid Arthritis.
In press.
2. Ropes, M. et al.: Proposed diagnostic
criteria for rheumatoid arthritis. Ann.
Rheumat. Dis. 16:118, 1957.
3. Cobb, S. and Lawrence, J.: Towards a
geography of rheumatoid arthritis. Bull.
Rheumat. Dis. 7:133, 1957.
4. Rubin, T. et al.: The use of interview
data for the detection of associations
in field studies. J. Chron. Dis. 4:253,
1956.
5. King, S. H. and Cobb, S.: Psychosocial
factors in the epidemiology of rheumatoid arthritis. J. Chron. Dis. In
press.
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