A six-year-old girl who died after becoming infected with swine flu died of septic shock as a result of tonsillitis, it was announced today.

Despite the post-mortem, however, it is still not known how much the flu virus contributed towards Chloe Buckley's death.

Chloe, who died on July 9 in West London, is among 29 Britons whose deaths have been linked to the H1N1 virus which is spreading through the country.

The results of the post-mortem investigation confirmed that she had tested positive for the virus but the official cause of death was given as “septic shock as a result of tonsillitis infection” caused by a common bacteria, streptococcus A.

It is not clear from the findings whether swine flu made her vulnerable to other infections or complications.

Simon Tanner, the director of public health at NHS London said: “Chloe was also found to have the swine flu H1N1 virus. It is not possible to say to what degree swine flu contributed to her death.

“We would once again like to extend our deepest condolences to Chloe's family at this difficult time and ask that the media respect their wishes to be allowed to come to terms with their loss in private.”

Chloe was reported to have first complained of a sore throat just 48 hours before her death at St Mary's Hospital, Paddington.

Mark Porter, The Times Doctor and a GP in South Gloucestershire, said that there was growing evidence that influenza A infection such as swine flu could increase a person's susceptibility to other infections.

“It sounds like Chloe had swine flu, which may have weakened her immune response to streptococcus A, a common bacteria and cause of sore throat — so-called ‘strep throat'," he said.

"Research has shown that the influenza A virus can weaken the body's natural defences to infections caused by common bacteria like streptococcus. Septic shock indicates that the bacterial infection had spread to the blood stream (septicaemia) and causing overwhelming infection

"The vast majority of cases of sore throat and tonsillitis are self limiting and get better without treatment, but in exceptional cases they can progress to much more serious infections, and having swine flu may make that more likely.

"Even so, septicaemia of this type remains a very rare complication of flu - pandemic or otherwise."

Of those who have died after being infected with swine flu, including four children and two mothers who died shortly after giving birth, all except one - an unnamed man from Essex - were known to have been suffering from underlying health problems.

Chloe’s parents Michael, 40, and Jacinta, 37, previously said they were “disappointed” at newspaper coverage which brought their daughter's care into question.

They said: “We are obviously very distressed at the loss of our fun-loving baby girl. Nothing can replace her.

“We are satisfied that the medical care Chloe received at all times was appropriate, and are disappointed with the stories that have been printed that suggest otherwise.”

Chloe was a pupil at St Catherine's School in West Drayton, London.

Head Sara Benn said earlier that it was “impossible to put into words the sorrow that the whole school feels”.

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