Tweeting a photograph of Lord Bathurst surrounded by his family outside their home, she wrote:
Now Lord Bathurst has spoken out to highlight the dangers of septicaemia and praise the staff who brought him back from the brink.
"I hope my experience will highlight the terrible effects of septicaemia and the symptoms," he said.
"Whilst my recovery will eventually be realised, I am under no illusion as to how close I was to losing my life and it is vitally important that we all familiarise ourselves with the causes, so it can be identified and treated fast."
Lord Bathurst, who hosts the Vale of the White Horse Hunt every Boxing Day, was admitted to Cheltenham General Hospital on July 26 after complaining of acute joint pain and high fever.
Lady Bathurst said doctors think he caught an infection from a deer fly or a Blandford fly on the estate, which is home to Britain's oldest polo ground, Ivy Lodge, where members of the Royal Family have frequently played.
She said: "It is suspected his infection came from an insect whose bite can cause severe repercussions.
"He became increasingly ill, and three days later, he suffered multi-organ failure and had to be rushed to the Department of Critical Care in Cheltenham."
Lord Bathurst then spent eight days in an induced coma to allow his system to fight the critical infection.
The Countess said her husband's life "hung in the balance" for four weeks but that, "against all odds", he eventually began to recover.
He was transferred to a general ward in Cheltenham, before spending a month in the Bone Infection Unit at John Radcliffe Hospital in Oxford.
Lord Bathurst, who is temporarily confined to a wheelchair, returned home last week and will be undergoing treatment to rebuild his hip and pelvic area in January.
His prosthetic hip was removed after it was identified as the breeding ground for the infection, leaving him without a hip or complete pelvic joint until his operation
Lady Bathurst, an official representative of the Queen, praised the NHS for saving her husband's life.
"It was a truly frightening time for us, and, to be honest, I don't remember much of it as I was in a state of total shock. But the NHS was magnificent," she said.
"The doctors and nurses were absolutely amazing once the diagnosis had been confirmed and their care, determination and commitment, not only to my husband, but also to me personally, was second to none. We are both incredibly grateful and humble for all they did."
The Bathurst family traces its origins to Sussex, but lost its castle and estates there during the Wars of the Roses, when Laurence Bathurst was executed by Edward IV in 1463, for siding with the Lancastrians.
Lord Bathurst has hosted polo matches for Princes William and Harry at Ivy Lodge, home of Cirencester Park Polo Club.
In one memorable incident, Lord Bathurst's father, the eighth Earl Bathurst, gave Prince William a telling off when he was overtaken at high speed by the then 20-year-old Prince's Volkswagen Golf after a polo match at the estate in 2003.
Clarence House issued a formal apology to Lord Bathurst on William's behalf.
