Prosecutors in Florence opened an investigation on Tuesday after it emerged that a hospital in the city transplanted organs from an HIV-infected woman into three hitherto uninfected patients.
The dramatic mistake at the Careggi university hospital was announced publicly soon after doctors became aware that the result of an HIV test on the donor's blood had been incorrectly written on a key document.
"The probability of infection in the receivers of the organs is high," admitted Franco Filipponi, head of the organisation which coordinates transplants in the Tuscany region.
"This is a terrible situation," said Mauro Marabini, head of the Tuscan hospital. "I can assure everyone that none of us slept last night and it will be hard to do so for a long while yet".
Experts said it would take a year before tests could establish whether or not the three patients - whose identities are being kept secret - had contracted HIV as a result of the transplants.
The donor was a 41-year-old woman who died of a brain haemorrhage, apparently unaware that she had the AIDS virus.
Florence's chief prosecutor, Ubaldo Nannucci, said he had ordered enquiries in order to "gather information" on the causes of the incident.
His office will try to establish whether there are grounds for pressing charges against the hospital.
The incident was a huge blow to the image of Tuscan medical care, which has in the past boasted about the efficiency of its transplant system. Tuscany handles more transplants a year than any other Italian region.
Regional and national officials tried to reassure Italians about the safety of transplant operations and public health services in general.
"In over 40 years the singular case in Florence is the first of its kind," said Health Undersecretary Antonio Gaglione. "I wouldn't talk about a crisis in health care but a fatal human error".
Italy's hospitals are regularly accused of failing to provide adequate services.
Last month the nation learned with horror that a 16-year-old girl had gone into a coma and died after a power cut hit the Calabrian hospital where she having her appendix removed.
According to lawyers for the girl's family, the power loss meant the respirator to which the patient was attached switched off and she went without oxygen for up to five minutes.
Prosecutors have also launched an enquiry into this case and the health ministry has vowed to establish the truth.
