The company, which employs more than 41,000 people, said the vast majority of its pubs had recorded no positive tests for the virus.
Wetherspoon's boss Tim Martin said 811 pubs have reported no positive tests, 40 pubs have reported one, six pubs have reported two, two pubs reported three and two pubs reported four.
The firm said most of the reported cases have been mild or asymptomatic and 28 of the 66 employees have already returned to work, after self-isolating in accordance with medical guidelines.
Wetherspoon said it has invested around £15 million in its social distancing and hygiene measures.
Mr Martin also told investors on Monday he believes the safety of pubs during the pandemic has been "widely misunderstood".
He said trading was "very quiet" over the weekend, before the Government tightened restrictions on larger social gatherings with the new "rule of six" from today.
The new rule means people could face fines of up to £3,200 if they are involved in social gatherings of more than six people.
Mr Martin said: "Trade was very quiet over the weekend, as the public weighed up the evidence about the alleged dangers of going out – Wetherspoon sales were 22.5% below the equivalent Saturday last year."
Trade groups, including the British Beer & Pub Association, said the new rule will halt the recovery of hospitality firms without extended financial support for the sector.
The chain said about 32 million people have visited its pubs since it reopened the doors at the start of July.