The changing epidemiology of chickenpox in Alberta.
BACKGROUND
Varicella vaccine was licensed in Canada in 1998. The province of Alberta introduced a universal publicly funded varicella vaccination program in 2001.


OBJECTIVE
To describe the epidemiology of non-fatal cases of chickenpox for which publicly funded health services were utilized for the period 1986-2002.


METHODS
We used the records of Alberta's universal, publicly funded health care insurance system to identify cases of chickenpox for the period 1986-2002. The earliest dated utilization of a health service for which there was an ICD9-CM code of 052.xx or an IC10-CA code of B01.xx was used as the date of illness onset. Denominators for rates were estimated using mid-year population estimates from the Alberta Health Care Insurance Registry. Age-specific rates were estimated for each year.


RESULTS
The crude incidence of chickenpox significantly declined over the period 1994-2002, most steeply after the year 2000. The incidence of chickenpox varied by age group and year and there was evidence of age-group-year interaction. Among those aged 5-19 years, chickenpox incidence began to decline prior to vaccine licensure in Canada. Among those aged less than one year and those aged 1-4 years, the incidence increased until 1999 when a decline began. Over the period 0.8% of cases were hospitalized.


CONCLUSIONS
Chickenpox rates began to decline prior to the introduction of the publicly funded vaccination program; however the declines in rates among the youngest age-groups are consistent with a vaccination program effect.
Russell
M L
ML
Department of Community Health Sciences, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta, Canada T2N 4N1. mlrussel@ucalgary.ca
Svenson
L W
LW
Yiannakoulias
N
N
Schopflocher
D P
DP
Virani
S N
SN
Grimsrud
K
K
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000416:Alberta / Q000453:epidemiology; D002644:Chickenpox / Q000453:epidemiology* / Q000517:prevention & control; D019433:Chickenpox Vaccine; D002648:Child; D002675:Child, Preschool; D003627:Data Interpretation, Statistical; D016208:Databases, Factual; D003695:Delivery of Health Care / Q000191:economics; D005260:Female; D006760:Hospitalization; D006801:Humans; D007223:Infant; D008297:Male; D032541:Mass Vaccination / Q000331:legislation & jurisprudence / Q000639:trends; D008875:Middle Aged; D009313:National Health Programs; D012621:Seasons; D012737:Sex Factors
D019433:Chickenpox Vaccine