Incidence of Autism Over Time
Epidemiology * Volume 17, Number 1, January 2006
Letters To The Editor of the NY Times
A dramatic rise of 4-fold or more in the
incidence of "diagnosed" autism during the decade from the late 1980s
to the late 1990s is well documented in Britain, parts of the United
States, and Denmark.
The evidence for this conclusion is
reviewed in an article that also provides a credible explanation for
this increase.1 Here, we extend the estimates of incidence of diagnosed
autism based on the General Practice Research Database (GPRD) to
include calendar years through 2004 to determine whether the incidence
has continued to increase or has leveled off. Our data source was the
UK population-based resource GPRD.2 GPRD computer-recorded diagnoses of
autism have been shown to be valid in 80% or more of cases.3,4
Criteria for inclusion in this
analysis were very similar to those used in our previous studies
on incidence of autism.1 The base population consisted of males age 24
to 59 months who had been registered by a practice by 18 months of age.
Cases of autism were required to have a first recorded diagnosis from
24 through 59 months (age 2- 4 years).1 Person-time of follow-up for
each child began accumulating at age 24 months and continued until the
months of age. We calculated annual autism
incidence rates among children in this 3-year age range for each
year from 1992 through 2004. Confidence intervals were calculated
using modified Byar's formula.5 Trend analysis was conducted using
Poisson regression model.
There were 308 incident cases of autism
identified from 1992 to 2004 (440,332 person-years in the base
population). We excluded 6 potential cases with evidence of severe
organic brain disease before the diagnosis of autism. Before 1996 there
was a steady increase in the annual incidence of autism of
approximately 20% (incidence rate ratio. 1.17;
95% confidence interval.
1.06 -1.30; Fig. 1). The incidence rate ratio estimates the annual
relative increase in autism incidence using the first year of interest
as the reference.
After a peak incidence in 1999, the
incidence rate remained stable from 2000 through 2004 (0.99; 0.88
Wakefield et al.6 in 1998 published a
small series of case reports that suggested a causal connection between
measles-mumps-rubella (MMR) vaccine and the risk of autism. This report
was followed by Taylor et al.7 in 1999, who reported a progressive
increase in the incidence of "diagnosed" autism as high as 33-fold in
cohorts of children 0 to 5 years of age born in a region of England
during the years 1979 through 1992. Taylor and colleagues concluded
that expo sure to MMR vaccine did not explain this dramatic rise.
A series of subsequent results based on the GPRD published in
2001 8 and 2003 1,9 documented that the apparent progressive increase
in incidence of diagnosed autism in boys age 2- 4 in the early 1990s
continued until 1999.1,9 These articles also provided fully convincing
evidence that neither MMR nor indeed any vaccines were responsible for
the dramatic rise in diagnosed autism over the course of time.1,8 The
results1 provided evidence that the rise in diagnosed autism was the
result of a change in criteria for the diagnosis at the clinical level.
In the current study, we have extended
our previous findings of
an increasing cumulative risk of diagnosed autism of 20% per year in
Britain in the 1990 birth cohort to the 1996 birth cohort9 and have
found the increase in incidence has indeed leveled off in the years
2000 to 2004 (incidence rate ratio . 0.99). We also note that a major
increase in the incidence of diagnosed autism occurred among 2- to
4-year-old boys, from approximately 5/10,000 person-years in 1998 to
more than 10/10,000 person-years in 1999 —1 year after the published
article of Wake.eld6 that received extremely heavy media attention.
This finding provides further credence to the proposition that the
diagnosis of autism is influenced by clinical perception and awareness
of the symptoms, as well as by the public pressure that characterizes
the tendency to make this diagnosis.
Hershel Jick Kathleen J. Beach James A.
Kaye Boston Collaborative
Drug Surveillance Program Boston University School of Medicine
Public Health University of
Massachusetts Amherst, Massachusetts
1. Jick H, Kaye JA. Epidemiology and possible causes of autism.
Pharmacotherapy. 2003;23: 1524 -1530.
2. GRPD. Full Feature GPRD -The General Prac¬tice Research
Database. Available at: www. GPRD.com/home. Accessed October 12, 2005.
3. Black C, Kaye JA, Jick H. The relation of childhood gastrointestinal
disorders to autism: a nested case-control study using the UK Gen¬
eral Practice Research Database. BMJ. 2002; 325:419-421.
4. Smeeth L, Cook C, Frombonne E, et al. MMR vaccination and pervasive
developmental dis¬orders: a case-control study. Lancet. 2004;364:
5. Rothman KJ, Boice JD Jr.
EpidemiologicAnalysisWithaProgrammableCalculator(NIH • Volume 17,
Number1 , January 2006 Epidemiology • Volume 17, Number 1,January
2006 LetterstotheEditor Publication 79 -1649). Washington DC: US
Government Printing Office; 1979.
6. Wakefield AJ, Murch SH, Anthony A, et al. Ileal-lymphoid-nodular
hyperplasia, non-spe-ci.c colitis, and pervasive developmental dis¬
7. Taylor B, Miller E, Farrington CP, et al. Autism and measles, mumps,
and rubella vac¬cine; no epidemiological evidence for a causal
association. Lancet. 1999;353:2026 -2029.
8. Kaye JA, Melero-Montes MM, Jick H. Mumps, measles, and rubella
vaccine and the incidence of autism recorded by general prac¬
titioners: a time trend analysis. BMJ. 2001; 322:460-463.
9. Jick H, Kaye JA, Black C. Changes in risk of autism in the U.K. for
birth cohorts 1990- 1998. Epidemiology. 2003;14:630-632..
Aussie Aspie Jailed For Gun Imports, Ecstasy
By Lauren Ahwan http://tinyurl.com/9ftpf
An Adelaide father-of-three who
illegally imported enough firearms parts to make two automatic machine
guns and possessed more than 900g of ecstasy, has been jailed for seven
David Neil Modra, 39, spent about $1370
buying gun parts - that were valued at $28,000 - from the United States
over the internet.
Frequently, Modra, who did not even hold
a firearms licence, asked the senders to label the items as machine
parts or sports goods to avoid detection by customs officers.
However, suspicions were eventually
raised and officers searched Modra's Willunga home, south of Adelaide,
in 2003, where they also uncovered the drugs.
Modra had more than 500 ecstasy tablets
stuffed in plastic bags in a satchel and enough powder to make a
further 8784 tablets.
The South Australian District Court,
after earlier accepting Modra's guilty pleas to a string of firearms
and drug offences, today said the drugs had a street value of up to
Judge David Smith said Modra, who had an
Why Won’t Feds Regulate Mercury?
By Carolyn Raffensperger for Science For
The link between mercury poisoning,
eating fish, and brain damage came to the attention of many in the west
through W. Eugene Smith’s elegiac photos of Japanese children lying
twisted, gnarled, and blind in their mothers’ arms. Japan’s Minamata
Bay had been terribly contaminated with mercury from an acetaldehyde
plant. Mothers ate mercury-laden fish and passed on the toxic metal to
their vulnerable babies. Victims numbered in the thousands. But the
authorities did not recognize that pollution caused the terrible damage
until 1968, years after the tragedy started, largely because the
company hid the research of courageous scientists.
Like most enormous toxic tragedies —
Bhopal, asbestosis, or Love Canal — Minamata took a long time to wend
its way through the courts. There have been many suits against Chisso,
the company, but last year the Japanese Supreme Court also held the
state responsible for the spread of Minamata disease after January 1960.
The ruling was unique in establishing
government responsibility for some of the damage. Presiding Justice
Chemist Says Mercury Linked To
By Rob Zaleski http://tinyurl.com/a7kae
His detractors call him an alarmist.
"They hate me," Mike Wagnitz
acknowledged in an interview this week.
But if that's what it takes to get
people's attention, hey, call him an alarmist or anything else you
want, Wagnitz said with a laugh.
A senior state chemist, Wagnitz is
making health experts uneasy because of his public statements urging
people to think twice before getting a flu shot this season. He thinks
the shots are especially risky for pregnant women and young kids.
Why? Because about 95 percent of the
doses being distributed this winter contain thimerosal, the
mercury-based preservative that Wagnitz and others believe is
responsible for the startling increase in autism cases in the United
States since the early 1990s.
The federal government says that's
hokum, noting that despite years of study there's no scientific
evidence that mercury in vaccines causes autism. However, as a
precaution, the U.S. Public Health Service in the late 1990s asked
manufacturers to start phasing thimerosal out of childhood vaccines.
In fact, both the American Academy of
School Big's 'Seizure'
By David Andreatt for the NY Post
The superintendent of citywide
special-education services will be reprimanded for directing
subordinates to ignore subpoenas to testify about the future schooling
of an autistic boy who suffered a classroom seizure, education
Susan Erber, the superintendent of
District 75, ordered two of her underlings to defy repeated demands of
a Department of Education hearing officer for them to speak about
placing the boy in a school potentially better suited to his needs.
The directive came to light last month
when a department representative testified it was Erber's "policy" not
to allow witnesses to appear in person at a hearing,
How Asperger's Feels
By Kate Goldfield
When I was a freshman in college,
someone asked a friend of mine if I was autistic. Having almost no
knowledge about what autism was other than a dim memory of a "Rain
Man"-like character rocking in the corner and nonverbal, I was
appalled. How could anyone possibly think I was like that?
Two years later, I rediscovered the
subject of autism after seeing a Lifetime movie about it. I was
intrigued by some of the concepts in it and began reading everything I
could find about autism, purely out of intellectual interest.
I awakened to the notion that a lot of
what I was reading sounded like me. I learned that autism is actually a
spectrum disorder, which means that there are people who are affected
by it on different levels. I discovered something called Asperger's
Syndrome, which is high-functioning autism and markedly different in
its presentation from what we could call classic autism.
Asperger's Syndrome, or AS, I learned, have trouble reading social cues
and understanding say in
conversations, when to start speaking and when to stop speaking.