The Plymouth Diocese has 93 parishes
Catholic churches in Devon, Cornwall and Dorset have been advised not to offer wine during communion to help halt the spread of swine flu.
The Plymouth diocese told its priests they should offer only the consecrated bread directly into people's hands.
Letters from the Diocese went out last weekend, before it was confirmed two adults in Plymouth had the virus.
The Diocese said it took the step after the World Health Organisation upgraded the seriousness of the disease.
The Plymouth Diocese has 93 parishes stretching from Penzance and the Isles of Scilly in the west to parts of Bournemouth in the Dorset.
It is divided into five deaneries, Cornwall, Plymouth, Torbay, Exeter and North and East Devon, and Dorset.
There have been three cases of the virus in Devon, two people in Plymouth and a 12-year-old girl in Torbay.
In Cornwall there have been 10 cases, including nine pupils at Bolitho School in Penzance.
In Dorset two holiday-makers were diagnosed in Weymouth.