40 Patients Were Infected by a Hospital's Water Supply Across 6 Years

For seven years, a renowned British hospital has grappled with a serious bacterial outbreak in its water supply that, according to a coroner's inquest and a new scientific paper, was linked to two deaths and 38 other cases of infection.

The new paper, led by members of the UK Health Security Agency and the Royal Papworth Hospital's medical director, offers new detail into the outbreak. It is published in the journal Clinical Infectious Diseases.

In 2025, the BBC reported that two women died after developing infections that, a coroner's inquest heard, likely came from the water supply of the hospital where they were receiving lung transplants.

The inquest also heard that a third patient died, but did not determine whether this was connected to the outbreak.

Both women contracted the bacteria Mycobacterium abscessus following double lung transplants at the then-newly relocated Royal Papworth Hospital in Cambridge.

The women each received treatment for non-tuberculosis mycobacterial pulmonary disease, but died within a year after M. abscessus was first detected in their bodies.

The coroner's inquest concluded that for both women, the M. abscessus infection contributed to their death.

M. abscessus is a common contaminant that usually only causes problems when it can enter the skin or soft tissues via a wound, or when a person's immune system is weakened – as is the case in transplant patients.

It's also multi-drug resistant, which makes it difficult to treat.

A specialist heart and lung hospital like Royal Papworth, which offers heart and lung transplants, respiratory support, and cystic fibrosis treatment, is perhaps one of the worst places for an outbreak of this bacterium to occur.

A total of 40 cases of M. abscessus infection have now been linked to the hospital's outbreak, between May 2019 and June 2025.

Eleven of these cases occurred in lung transplant recipients; 11 in cystic fibrosis patients; 14 in patients with non-cystic fibrosis bronchiectasis; and 4 in other patient groups.

"Infections can take a long time to present, sometimes many years," explains Royal Papworth medical director, Dr Ian Smith.

"People can acquire an infection and get symptoms straight away, some may not get symptoms until many years later, and some may never get any symptoms at all."

Following the first detections, the hospital undertook environmental sampling, which revealed the outbreak stemmed from the new building's water system.

There was no sign of the bacterium on any swabbed surfaces or medical equipment tested.

By October 2021, the hospital had rolled out a number of control measures, which included installing filters on patient room showers and basin taps, warning vulnerable patients about the risks and offering safety advice prior to admission, and providing them with bottled water during their stay.

These measures reduced the incidence of infections, but did not eliminate them entirely.

"The outbreak strain had persisted and disseminated throughout the hospital, despite extensive control measures taken, with positive results obtained from four different floors," the paper's authors report.

The hospital also installed a hydrogen peroxide dosing plant and a UV treatment unit in the hope of killing the bacteria in the incoming water supply, but these interventions were unsuccessful.

Between 2022 and 2025, the UK Health Security Agency undertook another round of environmental sampling.

They swabbed and took water samples from drains, showers, toilets and taps around the hospital; they even sampled the air above toilets post-flush.

They found the point-of-use filters that the hospital had installed on taps were effective, with no mycobacterium to be found in samples from the filtered water – but patients were still at risk from drain traps and the toilets.

"Following extensive control measures, including point-of-use filters and biocide treatment, incidence fell from 12.8 to 2.2 cases per year," the paper's authors write.

"No further case has been identified since June 2025, coinciding with a review of enhanced flushing."

Dr Smith says current and future patients of Royal Papworth Hospital are now safe from Mycobacterium abscessus, with ongoing vigilance, surveillance, and patient and staff education.

Solicitor Jatinder Paul said patients were admitted to "this world-renowned hospital… in the hope of a better life", the BBC reported.

"The events that unfolded have been devastating for them and their families," Paul said.

"We send our heartfelt condolences to those patients and families affected," Dr Smith said.

"As has been acknowledged throughout this journey, we followed national guidance in place at the time for the testing and management of water safety and took immediate and robust action once the situation was identified."

The research has been published in Clinical Infectious Diseases.