A two-year-old girl was made ill by a transfusion of contaminated blood at the Prince of Wales Hospital.
The case echoes an earlier case of contaminated blood in a transfusion at Tuen Mun Hospital after which a man aged 52 died.
The girl's reaction to the transfusion manifested in symptoms including fever, low blood pressure, an elevated heartbeat and skin rashes on August 15 when she received a resection procedure for a pancreatic tumour at the hospital, a spokesman for the Red Cross Blood Transfusion Service said.
The girl was treated with a steroid, antibiotics and drugs to raise her blood pressure and her symptoms gradually subsided.
She was asymptomatic last night and in stable condition.
A lab test isolated the common bacteria Pseudomonas fluorescens in her blood and in the bag of blood used for the transfusion.
It was found that the blood had been stored at the hospital blood bank since July 26 before being transported to the operating theatre on the day of the transfusion.
Traces of the bacteria were also found on the surface of an expired blood bag at the blood bank.
The Red Cross Blood Transfusion Service has reviewed all blood disinfection procedures and blood products without finding any abnormality, but two samples taken from workstations also tested positive for the bacteria.
The Hospital Authority said microbiologist Professor Yuen Kwok-yung from the University of Hong Kong, asked to probe the case, found no conclusive evidence of how the bacteria entered the blood bag, but he said the bacteria might have entered through invisible micro-cracks in the tubing attached to the bag.
Yuen also pointed out that water condensate could form on the surface of a blood bag after it was taken out of a refrigerator. He urged hospital blood banks to avoid unnecessary exposure of blood bags to room-temperature environments.
In an earlier case of a blood transfusion being contaminated by the same bacteria at Tuen Mun Hospital in 2008, a report by an investigation panel concluded that the bacteria could have seeped into the bag from condensation on a container in transit to the hospital.
Various measures were introduced after the case, but medical lawmaker Dr Kwok Ka-ki said the latest case proved that they might be not be effective.
Kwok also said he was let down by the Hospital Authority, which appeared to be playing down the gravity of the case, as no investigation panel had been set up to look into the matter.
He said he would pursue the authority for a fuller explanation of the case if its initial response proved unsatisfactory.