Seventeen people were placed under investigation on Tuesday in connection with the deaths of several patients in a southern hospital who were given laughing gas instead of oxygen.
Two patients died last week at the hospital in Castellaneta near Taranto in the region of Puglia after being fed nitrous oxide, a common anaesthetic gas.
Prosecutors suspect the same blunder could be behind another six deaths on the hospital's coronary intensive care ward since it first opened on April 20.
Sources close to the inquiry said those under investigation included several local public health officials, three doctors, the engineer who designed the gas system and the head of the Puglia-based company Ossitalia which fitted the pipes connecting the hospital ward to external gas tanks.
Ossitalia CEO and founder Domenico Matera, whose company specialises in the installment of medical gas equipment, is already under investigation on possible manslaughter charges in connection with the death of another patient at a Tuscan clinic.
The 73-year-old patient died at Siena's Le Scotte clinic on February 27 after a gas tube mix-up.
Inspections were under way on Tuesday in some 50 hospitals across Italy where gas equipment has been installed by Ossitalia, including Le Scotte.
Health ministry officials also carried out an inspection at the headquarters of Ossitalia in Bitonto near Bari.
Police swooped on the same offices on Monday, seizing documents linked to the Castellaneta hospital contract and the installed gas system.
Matera's lawyers stress that the system was finished and successfully tested in March 2005, when the hospital opened after 20 years of stop-start construction.
Ossitalia's lawyers say other firms were involved with the gas system between 2005 and April 2007 when the coronary ward was opened.
The company has provided police with a copy of a letter it sent to local health officials in October 2005 disclaiming all responsibility for the proper functioning of the system because other firms had been called in.
Autopsies are to be performed on the two most recent deceased patients, 73-year-old Cosima Ancona, who died last Friday and 82-year-old Pasquale Mazzone, who died two days earlier.
Mazzone's death failed to arouse suspicion because of his general poor health, doctors said. The previous deceased patients were also elderly and frail, they said.
But Ancona unexpectedly died before doctors' eyes during a minor operation for heart arrhythmia when her face mask sent fatal doses of nitrous oxide into her lungs instead of oxygen.
Prosecutors have ordered the bodies of the six other patients who died on the ward to be exhumed for autopsies.
The leading investigator, Taranto chief prosecutor Aldo Petrucci, said the Castellaneta hospital deaths appeared to be the result of a "macroscopic error" in the way the hospital gas system was installed.
Health Minister Livia Turco described the Puglia deaths as an "appalling tragedy", saying that "whoever made a mistake here will pay dearly".
STRING OF ERRORS BRING HEALTH SERVICE UNDER SCRUTINY.
The case dealt a fresh blow to public confidence in Italy's health service, which has been beset by a string of errors and apparently avoidable deaths over the past year.
In February, three patients at a Tuscan hospital were given transplants using organs from an HIV-positive donor.
In another headline case in January, a 16-year-old girl in Calabria entered a fatal coma when a power cut occurred in the hospital where she was being operated on for appendicitis.
Every year, between 4,500-7,000 patients die in Italy because of infections contracted while in hospital.
Hospital infections are considered a factor in another 21,000 patient deaths while up to 700,000 patients contract non-fatal infections.
Reports of poor hygiene and low safety standards sparked a nationwide inspection of public hospitals two months ago.
Less than half were given a clean bill of health, with 36.4% reported for breaching administrative norms, 17.4% for breaching building norms and 7.5% for breaching hygiene and cleanliness norms.
Southern regions were found to be the worst, with hospitals in Sicily, Calabria, Lazio around Rome and Campania around Naples proving the dirtiest.
