Hospitals have received guidance on harmful strain of a bacteria that is infecting growing numbers of patients.
Decontamination may be necessary in some hospitals
Acinetobacter is not a new bug - but experts are worried because the bacterium is becoming resistant to common antibiotics.
It is found in water, soil and sewage and is typically harmless in healthy people but can be dangerous in people already weakened by illness.
The Health Protection Agency advice includes isolating infected patients.
In some circumstances, it might be necessary to close infected hospital wards for decontamination, it said.
Laboratories regularly test samples of all forms of bacteria which affect patients.
The number of samples of acinetobacter that were found to be resistant to many antibiotic treatments increased from seven in 2002 to 22 in 2003.
Of those 22, 17 were found in five London hospitals, including St Mary's in Paddington.
Altogether, there were 1,087 reported cases of patients having the acinetobacter bacteria in their bloodstream in England, Wales and Northern Ireland in 2003, up 6% from the previous year.
Patients at particular risk include those staying in intensive care units and burns units for prolonged periods.
If acinetobacter gets into the bodies of the sick it can cause pneumonia, bacteraemia (blood stream infection), skin and wound infections, or urinary tract infection.
The HPA stressed that acinetobacter did not pose a risk to hospital staff or to family members or close contacts of an affected patient.
A spokeswoman said the agency had set up a working party to monitor reported outbreaks of drug-resistant strains and was looking at a new group of antibiotics as a possible way of tackling the bug.
"The numbers of reported cases are a lot lower and it tends to be a lot more choosy about the patients it affects.
"And it generally affects patients who are very sick in intensive care or burns units."
She added: "We will always be concerned about any infection that causes illness and could lead to deaths in hospitals, but it is not happening on the scale of MRSA at the moment."
A spokeswoman from St Mary's Hospital said 101 patients have been recorded as carrying the bug at the hospital between October 2004 and now.
"That figure represents patients who are carrying the bug, but not necessarily sick because of it.
"It can be a difficult infection to treat and presents problems for patients who are already very sick.
"At present, there are 10 patients carrying this infection in the hospital; they are being appropriately managed and cared for in isolation rooms.
"By using stringent infection control precautions and screening patients in the few areas of the hospital that have been affected, we feel we are closer to halting its further transmission."
She added: "Of all the patients who have died at St Mary's since October, 39 have been registered as acinetobacter baumanni positive.
"In not a single case can we say acinetobacter was the cause of their death. This is an important point as these were all patients with multiple health problems."