When London's Evening Standard splashed news of a winter beds 'crisis' across its front page on two consecutive days towards the end of last month, the Department of Health's media rebuttal unit swung into action.
The unit is an innovation of the current government - and not one which finds much favour with the national newspapers' health correspondents, who feel under attack for writing stories which reflect badly on ministers.
As director of communications, Ms McCallum's brief includes the unit - but its avtivity may prove to be a flashpoint as this is the media work in which ministerial special advisers tend to get involved. So how does it operate?
The Standard's stories had been damning. On day one, it had led with the claims of a consultant at St George's Hospital in Tooting that patients had been left on trolleys in accident and emergency while waiting-list work took priority. It followed up with the allegation that London's hospitals had enough beds - they just did not have enough nurses to staff them.
As often happens when the Standard - and other national newspapers - run stories perceived to be critical, the response was almost immediate, with ministerial special adviser Joe McCrea calling the paper to make a complaint.
The rebuttal unit followed this up with widely distributed press releases taking issue with both days' stories - the first was a routine recital of the extra money being spent on London's hospitals, and in particular on St George's.
It was accompanied by a letter from Philip Aylett, deputy director for news at the DoH, to the Standard's editor complaining that the paper had failed to contact the press office until 'the story was written and printed'.
Mr Aylett says he was in the room at the time Mr McCrea made the phone call to the Standard. 'I heard nothing that was either intemperate or abusive.'
He adds: 'I sent the letter because they didn't provide balance from our point of view. It worked in the case of the Standard because they carried our comment in later editions.'
Standard health correspondent Jo Revill is not impressed. 'We checked with the hospital concerned, and if we have done that we have done our job.' She feels no obligation to check with the DoH on every NHS story, she says.
But it was the second press rebuttal notice which really raised her hackles.
It included a statement by Graham Hayter, head of the NHS Emergency Beds Service - and the main source for Ms Revill's story - effectively dissociating himself from the main allegations in the report.
'I did not say that hospitals have no nurses or that there are too few nurses. I was reporting what hospitals are saying to us,' said Mr Hayter's written statement.
'I did not say that the situation could worsen in January. I said that January was traditionally a time of predictably high activity involving health and social services and we would have to wait and see what happens then.'
The construction put on it by many journalists who read the press notice was that Mr Hayter had been leant on. Asked whether this is the case, Mr Aylett says he had no contact with Mr Hayter, but adds: 'I wouldn't have thought so.'
'I am worried about the idea that if I have told them I have spoken to someone they imediately phone that person up to get them to say the reverse,' says Ms Revill.
'That puts people under huge pressure, and it makes us even less likely to check with the DoH.'
Mr Aylett says of his complaint to the Standard that 'the matter is now closed'.
But Ms Revill believes that such complaints merely add to a bunker mentality on both sides - a problem she believes to be worse at the DoH than other government departments.
In the meantime, however, the story disappeared from the front page of the Standard and every other paper - not because of anything the DoH did, but because bombs had started to fall on Iraq.