Data Collection

A quarterly questionnaire consisting of two parts was sent to the InVS:

• a summary of overall serological activity, surveillance activity, and the number of positive tests,

• a summary of the characteristics of each confirmed positive test (type of test, technique used, sex, and age of the individual).

Participation

A laboratory’s participation was defined as having completed at least one quarterly questionnaire.

Laboratories were defined as continuously participating if they had completed all quarterly questionnaires since the surveillance program began in the first quarter of 2008.