A hospital is at the centre of a multi-agency investigation after a patient with Legionnaires' disease died.
The patient, who has not been named, died on Saturday at Basildon University Hospital in Essex, with the provisional cause of death being given as pneumonia.
Essex Police and the Health and Safety Executive (HSE) are now probing the death while hospital officials have launched their own inquiry. The Health Protection Agency (HPA) has also been informed about the incident.
The person was diagnosed with the infection during the week prior to their death, according to the hospital.
A hospital spokesman said: "Following the patient's death at the weekend, HM coroner for Essex and Thurrock ordered a post mortem to determine the cause of death and Essex Police has launched a joint investigation with the HSE."
A police spokesman said officers and the coroner had instructed that no information about the dead patient, including age and sex, be released.
He said: "A joint investigation by Essex Police and the Health and Safety Executive has been launched following the death of a patient at Basildon University Hospital. The investigation was instigated after police were contacted by the Health and Safety Executive on Monday, August 22 after a patient died at the hospital on Saturday, August 20.
"A post-mortem examination was carried out on Tuesday, August 23 and a provisional result showed that the patient died from pneumonia. However, further tests are now being conducted to establish a precise cause of death."
Anybody can contract Legionnaires' disease, which is a potentially fatal form of pneumonia. But it principally affects those who are susceptible because of age and sickness.
The disease is caused by the bacterium Legionella pneumophila and related bacteria that can be found naturally in environmental water sources such as rivers, lakes and reservoirs. They may also be found in purpose-built water systems such as cooling towers, evaporative condensers and whirlpool spas.