prevalence rate for the Empiric criteria (Reeves, 2005) is 9.69 times the
Fukuda rate***. Put another way, only 10.31% of those who satisfy the
empiric definition would satisfy the Fukuda definition." This is relevant
for the XMRV testing of the CDC cohort, for example]
I am often hearing it said that the prevalence of
- CFS (Fukuda definition) is 1 million adults in the US
and for
- the Empiric criteria (Reeves, 2005) (which Reeves says is a version of the
Fukuda definition so the language is confusing) the prevalence is 4 million,
or 4 times the rate
i.e. 1 of 4 of those with the empiric definition would satisfy the normal
Fukuda definition.
However, I don't believe that is really correct - I think there is probably
a much bigger disparity in a random population cohort like the Georgia
cohort.
I thought people might be particularly interested in this now, given the
XMRV
testing of the CDC samples.
Of course, I think it is also relevant for dozens of studies that have been
published on the Wichita 2-day study and Georgia study since the end of
2005.
The prevalence rates found in the three random-number population studies
were:
- 235 per 100,000 (Fukuda definition) (95% confidence interval,
0.142%-0.327%)
(Wichita - mark 1 - not to be confused with the Wichita samples from the
2-day study which are almost certainly the ones that will be used for the
testing along with the Georgia samples) (Reeves, 2003)
and
- 422 per 100,000 (Fukuda definition) (95% confidence interval, 290-560 per
100,00)(Chicago) (Jason et al, 1999)
vs
2540 per 100,000 Empiric criteria (Georgia) (Reeves et al, 2007)
Comments:
One reason that may explain a lot of the differences between the two
Fukuda studies (Reeves 2003 and Jason, 1999) is the exclusions the CDC used:
-------
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC419502/pdf/1471-2377-4-6.pdf
Sample characteristics
One subject attending the clinic was dropped from analysis
because missing data did not permit scoring of any factor
in the SAQC. Demographic and clinical characteristics
of the remaining 339 subjects in the sample are shown in
Table 1 along with the distribution of these characteristics
by fatigue group. Over half the fatigued subjects (145/
277, 52.3%) as well as one not fatigued subject had exclusionary
medical or psychiatric conditions identified during
the clinical evaluation. Medical exclusions identified
during the clinic visit included abnormal blood or urine
tests, abnormal Romberg test, adrenal insufficiency, bladder
tumor, BMI = 47, cerebral palsy, chronic hepatitis,
emphysema, heart disease within 2 years of evaluation,
hypertension, hypothyroidism, inflammatory bowel disease,
kidney cancer, lupus, melanoma, uncontrolled diabetes,
rheumatoid arthritis, self-reported sleep apnea and
narcolepsy, and major surgery within the past year. Psychiatric
disorders included anorexia or bulimia nervosa,
bipolar disorder, delusional disorder, and major
depressive disorder with melancholic features.
-----
I believe many clinicians would find it strange to exclude people from the
diagnosis of CFS if they have an abnormal Romberg test - I have heard
clinicians say they use it to help confirm the diagnosis! Other exclusions
seem questionable e.g. hypertension.
So as I say, the exclusions may explain the difference between the two
Fukuda studies.
So possibly the easiest comparison is between the two CDC studies i.e. 235
vs 2540.
The second number is 10.8 times the first!
Technically, it is possibly the Wichita study missed a few people. The
Georgia study also brought in some unwell people who didn't look like they'd
fit the criteria on the phone interview but did fit the criteria eventually.
They said this would increase the prevalence rate by 11.5%. We do not know
if we would get such a jump with a stricter definition.
But if we used those figures, the prevalence for the Fukuda definition would
jump to 262 per 100,000.
In other words, the Georgia prevalence rate is 9.69 times the Wichita rate.
Assuming the population is similar one could say that ***the prevalence rate
for the Empiric criteria (Reeves, 2005) is 9.69 times the Fukuda rate***.
Put another way, ***only 10.31% of those who satisfy the empiric definition
would satisfy the Fukuda definition***.
If we decide to use an (unweighted) average from the Chicago and Wichita
samples, and increase it by 11.5%, then the prevalence rate per 100,000 is
1.115*(235+422)/2=366.28.
So the prevalence rate for the Empiric criteria (Reeves, 2005) is 6.93 times
the Fukuda rate. Put another way, only 14.42% of those who satisfy the
empiric definition
would satisfy the Fukuda definition.
And of course, many people think that the Fukuda definition itself isn't
perfect and for example, does not have a specificity close to 100% (i.e.
somebody could satisfy it and not have "ME" or "ME/CFS" (Canadian criteria)
or "proper" CFS).
Tom Kindlon
--------
Appendix 1:
In the 2005 paper that defined the Reeves empiric definition, we were told
that 16 satisfied the Fukuda definition and 43 satisfied the empiric
definition.
It might be tempting to use these numbers to estimate the percentage of
those who would satisfy the Fukuda definition in an empiric definition
cohort.
However, I don't believe one can do it.
For a start, there are question marks over 6 out of the 16 who satisfied the
Fukuda definition: Reeves said these were previously excluded for having
Major Depressive Disorder with melancholic features (MDDm) at some point in
their lives (see Table 2: "Recruitment and Current Classifications of 190
Subjects; 37 participants with medical or psychiatric exclusions other than
melancholic depression excluded"). The Fukuda criteria when published in
1994 said this was an exclusion if somebody ever had it in their lifetime.
The International study changed this to it had to have been resolved for
more than 5 years before the onset of the current chronically fatiguing
illness. Each of these 6 individuals had CFS or ISF on or before 2000, so
the MDDm would have had to have been resolved on over before 1995 (i.e. from
1995 to 2003 at a minimum). It is very doubtful that in all cases this was
the case. Indeed it seems quite possible it wasn't the case in any of the 6
cases.
So one doesn't know if 10, 11, 12, 13, 14, 15 or 16 in the cohort really
satisfy the Fukuda definition (it's 10 if one says they could never have
MDDm). This is of course still a useful figure as it means that if the
samples from the Wichita 2-day study are used for XMRV testing, between
23.26% (10/43) and 37.21% (16/43) of the samples would be from
Fukuda/International definition patients.
But the main problem with using the data in the 2-day cohort is that they're
not a random population group at all.
"This population-based case control study enrolled 227 adults identified
from the population of Wichita with: (1) CFS (n = 58); (2) non-fatigued
controls matched to CFS on sex, race, age and body mass index (n = 55); (3)
persons with medically unexplained fatigue not CFS, which we term ISF (n =
59); (4) CFS accompanied by melancholic depression (n = 27); and (5) ISF
plus melancholic depression (n = 28)."
Approx 1/4 of them had previously been diagnosed with CFS (Fukuda
definition):
So if one can't really tell anything about what percentage of Fukuda cases
one would find in the Georgia cohort using the Wichita 2-day study.
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