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Madsen KM, Lauritsen MB, Pedersen CB, Thorsen P, Plesner AM, Andersen PH,

Mortensen PB. (2003). Thimerosal and the occurrence of autism: negative ecologicalevidence from Danish population-based data. Pediatrics. Retrieved from

http://pediatrics.aappublications.org/cgi/content/full/112/3/604

Details: As in Stehr-Green, the authors looked into whether discontinuing the use ofthimerosal-containing vaccines in Denmark led to a decrease in the incidence of autism.

This studied also relied on data from the Danish Psychiatric Central Research Register onall psychiatric inpatient admissions since 1971, and all outpatient contacts in psychiatric

departments in Denmark since 1995. The patient population included all children

between 2 and 10 years old diagnosed with autism from 1971-2000.

Results: A total of 956 children were diagnosed with autism during the period. There

was no trend toward an increase in the incidence of autism during that period when

thimerosal was used in Denmark, up through 1990, the authors wrote. But from 1991until 2000, the incidence increased and continued to rise after the removal of thimerosal

from vaccines, including increases among children born after the discontinuation ofthimerosal

Authors Conclusions: Because the reported rate of autism continued to rise after the

removal of thimerosal from vaccines in Denmark, the authors said, Our ecological datado not support a correlation between thimerosal-containing vaccines and the incidence of

autism.

CRITIQUES OF THE STUDY

The Same Danish Database - Critics stated the obvious: This study was little more

than a second version of the Danish section included in the Stehr-Green paper, which waspublished one week earlier. The main flaw in that study, of course, was the major changein the Danish registryfrom including inpatient only cases, to including both inpatient

and outpatient cases.

Repeating the Swedish Mistake in Denmark - In order to address the issue of adding

outpatient cases in 1995, Madsen et al. went back and looked at inpatient cases only.

Among this small minority of cases, they reported the same trend with an increase in theincidence rates from 1990 until the end of the study period. The authors failed to providethese data in their study. And the sampling was essentially identical to the Swedish

analysis, in which the IOM committee (in addition to the authors) conceded that the

apparent increase inautism incidence could be due to changes in diagnostic criteria and

increasing awareness of autism and related disorders.

Weakness of Ecological StudiesThis was another ecological analysis, which, as theDirector of the CDC, Dr. Julie Gerberding, wrote to Congress: the contributions of such

studies toward establishing causality are limited.

A Very Low Autism Rate - Even if autism rates were shown to actually be increasingin Denmark, they were remarkably low both before and after thimerosal was removed.
http://pediatrics.aappublications.org/cgi/content/full/112/3/604http://pediatrics.aappublications.org/cgi/content/full/112/3/604http://pediatrics.aappublications.org/cgi/content/full/112/3/604


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According to the Madsen study, Denmarks prevalence rate was a tiny 1-per-10,000 - one

of the lowest rates ever reported -before thimerosals removal. By 1999 (with the

addition of outpatient cases) the rate rose to 4-6 per 10,000 - still very low -

comparable to US rates before thimerosal exposures in that country tripled, around 1990.

The rate was also at least ten times lower than the estimated 2000 US rate, 60-per-10,000.

Undisclosed Conflicts of Interest - SafeMinds and others criticized the inherent

conflicts of interest among some of the study authors. Two of them worked for theStatens Serum Institut, a Danish manufacturer of thimerosal containing vaccines.

According to its mission statement, Statens Serum Institut is a public enterprise

operating as a market-oriented production and service enterprise. In 2002, more than 80%of SSI profits came from vaccines. Still, this conflict was not disclosed by Pediatrics.

WHAT AN INTERNATIONAL TEAM OF SCIENTISTS SAID

In 2005, Joachim Mutter of the Institute for Environmental Medicine and Hospital

Epidemiology, in Freiburg, Germany and colleagues in the UK and US published a paperin Neuroendocrinology Letters that included a serious indictment of the study. It echoed

many of the same points made by SafeMinds and others, namely: (Mutter et al, 2005).

Autism counts were based on hospitalized, inpatient records in the first cohort and thenchanged in the middle of the study period (1995) to include outpatient records. Therefore,

the purported increases after 1994 may be explained by the additional recruitment of an

existing autism population that did not require hospitalization.

After 1992, the register added in patients from a large Copenhagen clinic, which

accounted for 20% of the caseload in Denmark. The patients from this clinic were

excluded prior to 1992.

The diagnostic category changed after 1993 from psychosis proto-infantilis of ICD-8

(code 299) to childhood autism of ICD-10. Another paper using the same inpatient

register reports that the psychosis proto-infantilis category includes inpatient cases thatdo not fulfill the criteria for autism.

Many of the children were between 79 years old, and most were over 4 years old,when recorded. But the onset of autism must occur, by definition in the diagnostic

criteria, before three years of age. The most widely used approach to assessing autism

trends is to use year of birth as the incidence time and to assess trends in autism rates

based on birth year of the study population rather than time at diagnosis or some othermeasure of incidence.

Another recent study performed by Madsen et al. reported Danish autism rates of 6 per

10,000 for children born in the 1990s (Madsen et al, 2002). These Danish rates are very

low in the 1990s compared to the United States. Madsen et al. also report inpatient rates

for the pre-1993 psychosis proto-infantilis at well below 1 per 10,000. This low rate


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would contradict the single published survey of autism rates from Denmark, which

indicated an autism rate of over 4 per 10,000 as far back as the 1950s.

Additional confounders were present in the U.S. with high prevalence of autism that

were not present in Denmark: Between 197092, the only childhood vaccine given in

Denmark until 5 months of age was the monovalent pertussis vaccine. In the UnitedStates, children were exposed to multiple doses of diphtheria, pertussis, tetanus, polio,

hepatitis B and haemophilus influenza B (Hib) vaccines before five months of age in the1990s.

WHAT THE MEDIA SAID:

The mainstream media portrayed the Madsen study as definitive. The New York Times

declared: Study Casts Doubt on Theory of Vaccines' Link to Autism and quoted the

CDCs Dr. Robert Davis as saying the evidence was clear-cut: If you remove cars from

highways, you'll see a marked decrease in auto-related deaths. If thimerosal was a strong

driver of autism rates, and you remove it from vaccines, you should have seen some sortof declineand they didn't (McNeil et al, 2003)

The Times also quoted Dr. William Schaffner, Chairman of Preventive Medicine atVanderbilt University in Nashville, as claiming that the study added to the whole mosaicof studies that have addressed this. Each is imperfect, but they all add up to this theme:

thimerosal is not the culprit.

The paper included a SafeMinds statement asserting that the researchers artificiallyboosted the number of cases by adding outpatients and those at a large Copenhagen clinic

to earlier inpatient figures. It also reported that two authors worked for a Danish vaccine

maker, suggesting a conflict of interest.

WHAT THE AUTHORS SAID:

Outpatients May Exaggerate Incidence - The authors conceded that, becausemany patients with autism in former years have been treated as outpatients this may

exaggerate the incidence rates simply because a number of patients attending the child

psychiatric treatment system before 1995 were recorded for the first time, and therebycounted as new cases in the incidence rates.

Greater Awareness, New Diagnostics Can Boost Numbers - The reported increase

in autism in Denmark may be attributable to more attention being drawn to thesyndrome of autism and to a change in the diagnostic criteria from the ICD-8 to the ICD-

10 in 1994.

Exposure Levels Were Lower Than US - Echoing criticism that the Danish data are

not comparable to other countries, such as the US where mercury exposures were greater,

the authors wrote: Our data cannot, of course, exclude the possibility that thimerosal at

doses larger than used in Denmark may lead to neurodevelopmental damage.


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WHAT THE IOM REVIEW SAID:

Limited Contribution - Adding additional outpatient cases into the Danish register

was noted as a potential problem. A reanalysis was conducted, limiting itself to inpatient

data only, and the authors found similar trends in autism rates, although the data were notshown, the IOM wrote. However, despite the reanalysis the authors stated that autism

incidence after 1995 may have been exaggerated due to the change in including

outpatient cases into the Danish Psychiatric Central Register. This limits the studyscontribution to causality.

SUMMARY: This study is perhaps the least informative of all the thimerosal studies.

The shifting definition of cases and limitation, at any point, of only autism cases that

were admitted to hospitals make this analysis thoroughly unreliable from the outset.

Compilation by SafeMinds

Madsen, K. Hviid, A. (2002). A population-based study of Measles, Mumps, and Rubella

vaccination and autism.New England Journal of Medicine. Retrieved from

http://content.nejm.org/cgi/content/full/347/19/1477

McNeil, D. (2003). Study casts doubt on theory of vaccines link to autism. The New

York Times. Retrieved from http://www.nytimes.com/2003/09/04/us/study-casts-doubt-on-theory-of- vaccines-link-to-autism.html

Mutter, J. Naumann, J. Schneider, R. Walach, H. Haley, B. (2005). Mercury and autism:accelerating evidence?Neuroendocrinology Letters Vol.26 No.5. Retrieved from

http://www.detoxmetals.com/content/AUTISM%20AND%20Hg/autism_reprint.pdf

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