In a tweet, Eastleigh candidate Patricia Culligan claimed a Liberal Democrat standing in another seat "deliberately became HIV positive yet free NHS care v costly".
She was referring to Paul Childs who is standing in Liverpool Riverside. He revealed he was HIV positive last week.
In appearing to question the cost of treating British patients Ms Culligan went further than Nigel Farage, who has controversially said foreigners with HIV should not be treated for free by the NHS.
The UKIP leader's comments during last week's TV debate were greeted with heavy criticism from some of the other leaders. He insisted it was right to "put our own people first".
Patricia Culligan removed her tweet and apologised after UKIP was contacted by the BBC on Thursday evening.
In a statement, the party said: "We wholeheartedly support the NHS being free at the point of access and kept publicly-funded.
"We have spoken to Ms Culligan and advised her to retract the comment which seems to conflate two very separate issues."
In a follow-up tweet she said she "sincerely" apologised for "any totally unintended offence" , saying she had misread a Mail Online article about Mr Childs.
She added: "I have nothing but sympathy for sufferers."
It is not clear though if she believes the NHS should ration or reduce treatment of British HIV sufferers.
UKIP almost won the Hampshire seat of Eastleigh in a by-election in 2013.
Ms Culligan was selected last September to fight it for UKIP.
The Liberal Democrats said her comment was "disgusting and deeply offensive".
A party spokeswoman said: "The Liberal Democrats will always stand up for the liberal British values of tolerance, generosity and decency."
For a full list of the candidates in Eastleigh please click here.
For the corresponding list in Liverpool Riverside please click here.

Homeland Security Secretary Jeh Johnson said his team had been in "constant" contact since the Paris attacks.
Elsewhere, hundreds are protesting over plans to clear away homeless residents in central San Francisco.
The Super Bowl is the climax of the American football season, and a crowd of 70,000 is expected for the game.
The Denver Broncos will be taking on the Carolina Panthers in the biggest National Football League (NFL) game of the year, as part of a landmark Super Bowl 50 - marking half a century of the big game.
Thousands of police and security officers are expected to be deployed across the San Francisco Bay area, which covers nine different counties. The game will be held in Santa Clara, about 40 miles (64km) south of San Francisco.
Officials say they are not responding to a specific threat, but have been urging the public to remain vigilant.
"We are always informed by recent events and what we see in the world situation," Mr Johnson told reporters earlier this week, referring to the deadly attacks in Paris in November last year which killed 130 people.
"The threat picture is different every February," he added, keeping a tight lid on further details of the security plans.
A senior NFL official, Jeffrey Miller, told Reuters that some 4,000 private security staff had been brought in to support police in securing the area.
Meanwhile, CNN reports the US Air Force is deploying two of its aircraft - an F-15 Eagle and a Cessna 182 - to provide air cover for the major sporting event.
The use of drones from flying within 32 miles of the Super Bowl stadium in Santa Clara, California, has also been banned between 14:00 and 23:59 PST on 7 February.
In a video to sports fans released on Thursday, the Federal Aviation Administration (FAA) warned the stadium is a "no-drone zone".
It comes as protests erupted this week over plans by the authorities to clear the streets of San Francisco of its homeless residents.
Some 200 people gathered in the city on Wednesday shouting "no penalty to poverty", and demanding the authorities do more to help the city's estimated 7,000 homeless people.
San Francisco Mayor Ed Lee indicated in August last year that they would make efforts to remove them, saying "they're going to have to leave".
But city officials insist they are offering alternative accommodation for homeless people before telling them to move - a claim protesters deny.
Another point of contention raised by the demonstrators is the $5m expenditure on the Super Bowl, as well as the millions spent on TV advertisements during the game, which some argue could have gone towards housing hundreds of homeless residents.
UKIP's candidate in a key general election seat has been forced to apologise after she appeared to question the cost to the NHS of treating British people who are HIV positive.
[NEXT_CONCEPT]
US officials in California have been seeking security advice from French officials, as the San Francisco area prepares to host the Super Bowl.