LONDON — Queen Elizabeth II was hospitalized Sunday over an apparent stomach infection that has ailed her for days, a rare instance of ill health sidelining the long-reigning monarch.
The queen will have to cancel a visit to Rome and other engagements as she recovers.
Outside experts said she may have to be rehydrated intravenously.
Buckingham Palace said the 86-year-old queen had experienced symptoms of gastroenteritis and was being examined at London’s King Edward VII Hospital — the first time in a decade that the queen has been hospitalized.
“As a precaution, all official engagements for this week will regrettably be either postponed or cancelled,” the palace said.
The queen’s two-day trip to Rome had been set to start Wednesday. A spokesman said the trip may be “reinstated” at a later date.
The symptoms of gastroenteritis — vomiting and diarrhea — usually pass after one or two days, although they can be more severe in older or otherwise vulnerable people.
Dehydration is a common complication.
The illness was first announced Friday and Queen Elizabeth had to cancel a visit to Swansea, Wales, on Saturday to present leeks — a national symbol — to soldiers of the Royal Welsh Regiment in honor of Wales’ national day, St. David’s Day.
She instead spent the day trying to recover at Windsor Castle, but appears to have had trouble kicking the bug. A doctor not involved in the queen’s treatment said that if medical officials determined that she is losing too much fluid, she would be rehydrated intravenously.
“Not everyone can keep up with oral hydration, so it is pretty routine to go to hospital and have a drip and wait for the thing to pass and keep yourself hydrated,” said Dr. Christopher Hawkey of the University of Nottingham’s faculty of medicine and health sciences.
Britain’s National Health Service says that the two most common causes of gastroenteritis in adults are food poisoning and the norovirus, a common winter bug that typically afflicts between 600,000 and 1 million Britons each year.
British health guidelines advise that people with the norovirus avoid work for at least two days.
Queen Elizabeth has ruled since 1952 and is Britain’s second-longest serving monarch, beaten only by Queen Victoria in terms of the number of years on the throne.
The queen’s husband, Prince Philip, 91, has been in the hospital several times, but the queen rarely has let sickness get in the way of her schedule. About five months ago she canceled an engagement because of a bad back.
The spokesman, who demanded anonymity because palace rules do not let her go on the record, said the last time Queen Elizabeth was hospitalized was in 2003 for a knee operation.
Ingrid Seward, the editor of Britain’s Majesty Magazine, said that the queen “probably agreed to be hospitalized in order to get better quickly.”
“Everybody will want to be wishing her a speedy recovery,” she told Sky News television.
The queen’s popularity has been high over the last two years. The wedding of her grandson Prince William to Kate Middleton, who are now known as the Duke and Duchess of Cambridge, in 2011 generated significant goodwill. The couple are expecting their first child.
The queen’s Diamond Jubilee celebrations last year cemented her popularity, as did her participation in the opening ceremony of the London Olympic Games, when she appeared with the fictional spy James Bond, portrayed by actor Daniel Craig, in a video sequence.