Health chiefs were today investigating a possible outbreak of legionnaires' disease at a hospital which was recently under scrutiny for blood-splattered equipment and an unusually high patient mortality rate.
The probe was launched at Basildon University Hospital in Essex after two patients were suspected to be infected with the bacteria.
Tests are now being conducted to discover the source of the suspected outbreak, a hospital spokeswoman said.
Swabs from both the patients, who were staying in different parts of the hospital, have been sent away to a laboratory for further analysis, she said.
"We are investigating two suspected cases of legionnaires' disease," said the spokeswoman.
"We do lots of testing for legionella in patients who have suspicious respiratory infections.
"We have had problems with the disease before so we are acutely aware of the risk of the bacteria. We have particularly high levels of control and are constantly performing checks and taking preventative measures."
She said the last outbreak of the disease at the hospital was in 2007.
"It is accepted by experts that it is practically impossible to eradicate the legionella bacteria completely on an ongoing basis from large and complex water systems," she added.
"It has to be contained and controlled by a continuous regime of precautionary measures that we strictly adhere to."
Legionnaires' disease is a potentially fatal lung infection that is caused by the bacteria legionella. The bacteria is commonly found in sources of water such as rivers and lakes but can sometimes find their way into artificial water supply systems.
It is contracted when small droplets of contaminated water are breathed in. It cannot spread from person to person.
Symptoms of the disease include headaches, fever, chills, muscle pain and coughs. It is estimated 10% of people who contract legionnaires' disease will die from complications arising from infection.
In November, inspectors from the Care Quality Commission criticised Basildon and Thurrock University Hospitals NHS Foundation Trust after they found blood stains on floors and curtains, blood splattered on trays used to carry equipment and badly soiled mattresses in the A&E department with stains soaked through.
Inspectors also found equipment being used repeatedly that should only be used once and resuscitation room equipment that was past its use-by date.
Other items found at the trust included blood pressure cuffs stained with blood, suction machines contaminated with fluid inside and out and apparent mould.
However, on December 23 the watchdog said that hygiene standards were improving and that the trust has taken action to address concerns about infection prevention and control.
It said further checks would be carried out on the trust, including unannounced inspections, to check that recommendations for improvement have been acted upon.