People who had a test processed at the laboratory between 8 September and 4 October will also be contacted and advised to get a test if they have symptoms.
Cysylltir â phobl a gafodd brawf a broseswyd yn y labordy rhwng 8 Medi a 4 Hydref hefyd a'u cynghori i gael prawf os oes ganddynt symptomau.