Directive 1999/35/EC provided that once in every 12-month period host States are to carry out a specific survey and a survey during a regular service.
Foráladh i dTreoir 1999/35/CE gur gá do na Stáit óstacha suirbhé sonrach agus suirbhé le linn seirbhís rialta a chur i gcrích uair amháin i ngach tréimhse 12 mhí.