The La Crosse-based Franciscan Sisters of Perpetual Adoration claim to have been praying night and day for the ill and suffering longer than anyone in the US, since 11am on August 1, 1878.
“When I walk into the chapel, I can feel this tangible presence kind of hit [me],” said Sr Sarah Hennessey, who helps co-ordinate the prayers.
The tradition of perpetual Eucharistic adoration, uninterrupted praying before what is believed to be the body of Christ, dates to 1226 in France, says Sr Marlene Weisenbeck.
Catholic orders have done it since then.
It grew in popularity in 19th century and again under Pope John Paul II, said Father Steven Avella, history professor at Marquette University.
The order started asking for community help in 1997, when the number of nuns began dwindling.
Nowadays, the sisters usually take night shifts and lay people cover the day, according to Sr Maria Friedman, who schedules two people every hour.
“Even the sisters go away frequently or take on other tasks,” she said.