It is believed to be the biggest outbreak of hepatitis outside a hospital in Britain since World War Two, prompting medical experts to call for greater regulation of private surgeries offering homeopathic and alternative medicines.
The clinic at the centre of the scare, the Finchley Alternative Medical Centre in north London, has suspended the treatment, known as autohaemotherapy, in which a small amount of the patient's blood is mixed with saline solution and re-injected through acupuncture points.
Barnet Health Authority is leading the investigation into the outbreak. The General Medical Council and the Health and Safety Executive are also making inquiries.
The practitioner at the centre of the scare, Dr Madhusudan Shivadikar, has tested negative for hepatitis B. A founder member of the Commonwealth Institute of Acupuncture and Natural Medicine and a former hospital doctor, he is co-operating fully with the investigation but declined to comment on the new development. The outbreak was first reported in the Independent in February.
Tests have been carried out on 230 people who attended the centre between July 1997 and this February. Barnet Health Authority says that of the 47 people with hepatitis B, 28 definitely caught the virus at the centre, and a further 19 almost certainly did. More results are awaited.
The testing programme has been widened after a woman who attended the clinic was found to have hepatitis C when she made a routine blood donation. A further 160 people who attended the clinic in the six months before July 1997 are now being traced and tested.
Dr Stephen Farrow, director of public health for Barnet Health Authority, said there was little doubt the hepatitis B infections were caused by the treatment. "We are as certain as we ever can be that the virus has come from a single source," he said. "The only common exposure is that all these people attended the centre at about the same time. We've identified the DNA strain of the virus involved and it is identical."
Hepatitis B causes inflammation of the liver and can lead to flu-like symptoms and jaundice. Hepatitis C can lead to cirrhosis of the liver.