Rising incidence of Kawasaki disease in England: analysis of hospital
admission data
Anthony Harnden, university lecturera, Bernadette Alves,
health services researcherb, Aziz Sheikh,
NHS research and development national primary care training fellowb.
a Department of Primary Health Care, Institute of Health Sciences,
University of Oxford, Oxford OX3 7LF, b Department of Primary Health
Care, Imperial College of Science, Technology and Medicine, London W2 1PG
Kawasaki disease is the leading cause of acquired heart disease in children
in the developed world and may be a risk factorfor adult ischaemic
heart disease.1 A fifth of untreated childrendevelop cardiac lesions during the acute phase of the disease.
The cause remains uncertain. Epidemiological studies support an
infectious agent inducing the disease in a genetically susceptible
minority. Superantigen toxins have been implicated. Reported incidencerates differ considerably throughout the developed world with
rates in Japan 10 times those in the United States and 30 timesthose
in the United Kingdom and Australia.2-4 Hospital
surveillancedata suggest the incidence of Kawasaki disease in Japan
has risenby over 50% between 1987 and 1998.2
To ascertain whether therehad been a similar rise in England, we
investigated trends inhospital admissions for Kawasaki disease using
routinely collectedstatistics from 1991 to2000.
The hospital episode statistics database provides information on every
inpatient admission to English NHS hospitals. Codingaccuracy and
reproducibility are better for acute conditions thanfor chronic
disorders.5
We examined all emergency inpatient admissions for children younger than
17 years primarily diagnosed as having Kawasaki diseasebetween
1 April 1991 and 31 March 2000. We excluded 293 interhospital
transfers to avoid duplication. Coding of diagnoses with ICD-10
(International Classification of Diseases, 10th revision) beganin
1995. We analysed admissions coded with ICD-9 code 446.1 andICD-10
code M30.3 separately and together. We derived overalladmission
rates specific to age from the 1999 estimates of thenational midyear
population. With monthly admissions as the dependentvariable and the
number of months from 1 January 1991 as the independentvariable, we
used linear regression to look at time trends overthe study period.
Monthly inpatient admissions for Kawasaki
disease from April 1991 to March 2000 in England
During the nine years there were 2215 emergency admissions in children with a
primary diagnosis of Kawasaki disease, 666 inthe four year ICD-9
coded period and 1549 in the five year ICD-10period. Median age at
admission was 2 (interquartile range 1-4)years. Almost two thirds
(61%) of children admitted were boys;this proportion was consistent
in all ages and across the studyperiod. Annual admissions increased
from 143 in 1991-2 to 308in 1999-2000.
The incidence per 100 000 children younger than 5 years doubled from 4.0 per
100 000 (95% confidence interval 3.4 to 4.8)in 1991-2 to 8.1 per
100 000 (7.1 to 9.2) in 1999-2000. The linearmodel (figure) provided
evidence of a significant increase inmonthly admissions:
0.15 (0.05 to 0.25; P<0.001) extra admissionsper month during ICD-9,
0.20 (0.07 to 0.32; P<0.001) during ICD-10,and 0.21 (0.17 to
0.25, P<0.001) in the two periodscombined.
Hospital admissions for Kawasaki disease increased in England between
1991 and 2000. It is possible that this reflects anincrease in
recognition rather than incidence. After the demonstrationin
1991 that in the United Kingdom only 7% of children with Kawasaki
disease received optimum immunoglobulin treatment, awareness ofthe
importance of early diagnosis has been heightened.3
The incidence of Kawasaki disease among English children may have truly risen
as it has in Japan. Explanations include a changein the infecting
agent or a shift in susceptibility among youngchildren. We recommend
improved surveillance of Kawasaki diseaseto record further rises in
incidence, to examine seasonal andgeographical variations, and to
report any changes in the patternof clinical severity or the rate ofcomplications.
Acknowledgments
We thank Tim Lancaster and David Mant for comments on earlier drafts of this
paper and Adrian Cook for help with the dataanalysis.
Contributors: AH and AS had the idea for this paper. All three authors
devised the study. BA analysed the data. AH drafted the paper and BA and AS
commented on the text. AH is guarantor.
Footnotes
Funding: AS is supported by a NHS research and development national primary
care trainingfellowship.
Yanagawa H, Nakamura Y, Yashiro M, Oki I, Hirata S, Zhang
T, et al. Incidence survey of Kawasaki disease in 1997 and 1998 in Japan.
Pediatrics 2001; 107: E33[Medline].
Dixon J, Sanderson C, Elliott P, Walls P, Jones J,
Petticrew M. Assessment of the reproducibility of clinical coding in
routinely collected hospital activity data: a study of two hospitals. J
Public Health Med 1998; 20: 63-66[Abstract].
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