The incidence of XXXX : correction of a common error.

@entity1 @entity992
BACKGROUND: Interest in the incidence of @entity992 (chickenpox) has increased since the discovery of an effective vaccine, but calculations to date have incorrectedly ignored the question of susceptibility. METHODS: We studied the occurrence of @entity992 in Italy on the basis of 33,343 @entity1 (age 0-14 years) cared for by 35 pediatricians between 1 October 1997 and 30 September 1998. The life-table technique was used to calculate the number of susceptible @entity1 . On this basis, we estimated the corrected age-specific and cumulative incidence. RESULTS: We identified 1749 cases among the estimated 21,783 susceptible @entity1 , for a crude incidence of 8.0% (95% confidence interval [CI] = 7.7-8.4). The rate age-standardized to the Italian population 0-14 years old was 6.8 (CI = 6.5-7.2). The incidence was more than 16% among @entity1 age 3-4 years and more than 4% for those age 1-10 years. Comparison of the usual method and our corrected method showed that the uncorrected method underestimates the crude annual incidence (5.2% 8.0%), shifts the peak incidence to earlier ages, and underestimates cumulative incidence (at age 14, 49% 67%). CONCLUSIONS: The use of our corrected method provides more valid estimates of the incidence of @entity992 than the ones that are currently available. Corrected estimates should be preferred to uncorrected ones in models to study the cost-effectiveness of universal vaccination against @entity992 .
