Age-Specific Attack Rate in Females during a Rubella Epidemic

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Abstract
In the winter 1967–1968 an extensive rubella epidemic occurred in Turku city and its surroundings. A collection of 298 serum specimens was available from females of various age groups in the area taken a few months before the epidemic started. Another set of 351 serum specimens was collected after the epidemic from identical female groups. The positive rate of HI antibody in the pre-epidemic series was 198/298 (66%), and in the post-epidemic series 293/351 (83%). The highest increase (from 42 to 71%) was in the group of 10–12 years, followed by the age groups 6–8 (from 26 to 43%) and 17–22 (from 76 to 90%). The highest infection rale among the susceptibles (HI <1/10) occurred in the group of 17–22 years (58%) and in the 10–12 years group (50%), whereas in the youngest age group it was only 23%. Calculations showed that of every 100 infected in the age groups studied, approximately 25 were in the group aged 6–8 years, 40 in the group aged 10–12 years, 20 in the group aged 17–22, and 15 in the two oldest age groups combined. Comparison of HI and CF results indicated that each specimen negative in the HI test was negative in the CF test, but 14% of CF-negative specimens were positive in the HI test.