Table 1 Brief description of the questionnaire used in the case control study

General farm information

Herd size

large or small

Fattening farm (only pig farms)

yes or no

Belong to a company group (only pig farms)

yes or no

People movement

Farmer visited other livestock farms

yes or no

Farm staff commuted from outside

yes or no

Veterinarians visited the farm

yes or no

Agricultural technicians visited the farm

yes or no

Staff of livestock related companies (such as drug companies) visited the farm

yes or no

Other livestock farmers visited the farm

yes or no

Other people (such as relative and town hall staff) visited the farm

yes or no

Vehicle movement

Feed transport vehicles visited the farm

yes or no

Farmer transported feed by own vehicle

yes or no

Carcass transport vehicles visited the farm

yes or no

Bedding transport vehicles visited the farm

yes or no

Farm management

Farm equipment (such as tractors and roll balers) were shared with other farms

yes or no

Manure was removed from the farm

yes or no

Farm location

Barn has physical barriers (such as a private house and clump of trees)

yes or no

A forest surrounds the farm

yes or no

Housing is located outside the farm

yes or no

Barns bordered by a road

yes or no