When Anthony, 82, fell ill after a spot of summer gardening, the GP said it was a virus that would pass in a few days. A week later, he was dead. His killer? A simple bag of compost.

Should bags of compost – as used by countless green-fingered Britons every day – carry warnings about a potentially deadly bacteria they could harbour?

Theresa Gilsenen, 79, from Storrington, West Sussex, believes they should. After Anthony, her beloved husband of 55 years, died in August last year, Theresa was stunned when health officials linked his death at 82 to a bag of garden compost he’d been using to re-pot an olive tree.

Anthony’s death was caused by Legionnaires’ disease, a severe lung infection.

While more commonly associated with inhaling droplets of water contaminated with the bacterium Legionella pneumophila – from hot tubs that haven’t been cleaned properly, for instance – the condition can also be caused by Legionella longbeachae, associated with soil, compost and potting mixes.

Now, just over a year on, Theresa, with the backing of her MP, Andrew Griffith, is calling for clear warnings about Legionella to be put on compost packaging.

Currently, most bags have a small label advising users to wash hands after use and avoid inhaling dust from the contents.

‘The warnings should be bigger and I’d like to see Legionnaires’ risk clearly stated on all compost bags,’ says Theresa.

‘It’s my life’s mission now to make other people aware of the dangers. Losing my soulmate has been horrendous.’

The first sign anything was wrong with Anthony, a retired businessman, came six days after he re-potted an olive tree.

‘He lost his appetite and was feeling tired,’ says Theresa. ‘The GP said it was a virus that would pass in a few days.’

But Anthony deteriorated. Two days later, at a second GP appointment he was diagnosed with pneumonia and prescribed antibiotics.

Despite the treatment, within another two days, his chest was more congested ‘and he was too tired to get out of bed’, recalls Theresa, who called NHS 111 and was directed to take him to A&E.

Anthony was well enough to joke with the other patients in the waiting room.

But within hours he developed multiple-organ failure and died, with Theresa and their two children, Edward and Louise, at his bedside.

‘He went downhill so quickly,’ says Theresa. ‘Before he died, we told him how much we loved him – I hope he could hear us.’

While the devastated family were making arrangements for Anthony’s funeral, Theresa received a call from the UK Health Security Agency (UKHSA) to say the hospital had identified Legionella longbeachae as the cause of his infection.

‘They took me through a diary of what Anthony had been doing before his death,’ says Theresa.

‘He’d re-potted the olive tree 12 days before he died, which I was told was consistent with the timing of the infection. I was told the compost was the likely source. It was such a shock.’

Legionella longbeachae is found in soil, compost and potting mix, and is named after the city in California where it was first identified in 1980.

As with Legionella pneumophila, which causes most cases of Legionnaires’ disease, Legionella longbeachae ‘can invade the cells in the lungs’, explains Jeremy Brown, a professor of respiratory infection at University College London. This causes a cough, shortness of breath and other flu-like symptoms.

Exactly how Legionella longbeachae might travel from compost into the lungs isn’t understood, adds Professor Brown – it may be that soil dust is inhaled, ‘but this isn’t proven’.

It can cause serious infection, with a higher rate of intensive-care admission and death than other causes of pneumonia such as flu – although there are too few cases from Legionella longbeachae to be sure of this statistically, says Professor Brown. Between 2017 and 2023, just 35 cases of Legionella longbeachae were reported in England and Wales – but ten people died, giving the infection a fatality rate of 28.6 per cent – compared with 5.8 per cent for the more common Legionella pneumophila.

But its symptoms can look like standard pneumonia, making diagnosis difficult – the only way to know for certain is testing a fluid sample from the lungs.

‘The key is for doctors to think it might be the cause and to ask for the microbiologists to look for it,’ says Professor Brown.

‘We will not do that routinely as it’s rare. The history of exposure to potting compost or soil is key.’

If Legionnaires’ disease from either bacteria is confirmed, the UKHSA has to be notified in order to prevent potential outbreaks.

It collected the bag of peat-free compost Anthony had used – this was found to contain Legionella longbeachae, though the strain wasn’t genetically identical to the one that made Anthony ill (the agency explained that while it’s possible the compost was the source, it can’t be certain).

Dr Tara Beattie, an environmental engineer with a focus on public health at the University of Strathclyde, researched Legionella longbeachae in commercially available compost after a cluster of infections in Scotland in 2013. She believes cases are being missed, as ‘the UK data is quite limited’.

Theresa is left wondering about the extent of the problem, too. ‘It was only because someone took a sputum sample from Anthony that the longbeachae bacteria was discovered,’ she says.

‘We’re a nation of gardeners – it does make you wonder whether there are other infections and deaths that are never discovered.’

Some researchers claim peat-free compost, increasingly popular with gardeners, is more at risk of Legionella contamination than peat-based compost.

Peat-free compost typically contains composted bark, wood fibre and coir (coconut fibre). Research in 1994 found Legionella in 80 per cent of the composted bark and sawdust samples tested – but not in pure peat.

‘But I don’t think there was ever definitive proof,’ says Dr Beattie, whose own work found Legionella longbeachae in both types of compost.

The risk is not confined to shop-bought compost. Legionella can be found in garden soil and homemade compost, too.

Storage conditions may also play a part. Research suggests that warm, humid conditions can help Legionella survive and multiply, raising concerns about bags left outdoors in hot weather or kept in sheds and greenhouses.

Serious infection from Legionella bacteria is more common among older people due to waning immunity and those with underlying health conditions such as heart disease and diabetes.

And a 2017 study found that people who have smoked were twice as likely to develop Legionella longbeachae infection as those who had never smoked.

‘But it can cause infection in healthy people as well,’ says Professor Brown.

Although Anthony had been diagnosed with a type of blood and bone marrow cancer in 2017, he was otherwise well.

‘He looked after himself and was very fit,’ says Theresa.

‘He’d go cycling on his electric bike for hours. He walked the dog every day and was always seeing friends and going to live music and classic car shows.’

Now Theresa is devoting her time to push for more prominent labelling on compost bags.

The current warnings about avoiding breathing in dust and washing hands after use are tiny – ‘How many gardeners would notice them?’ asks Theresa. Andrew Griffith says warnings about Legionella ‘could save lives’.

The company that produced the compost Anthony was using has agreed to change its labelling from 2027, making health and safety warnings more prominent.

And in a letter to Andrew Griffith, business minister Kate Dearden said that officials were contacting industry bodies and compost suppliers to make them aware of the risks and encourage them to review their packaging.

Theresa is adjusting to life without Anthony and recently moved.

She says: ‘I couldn’t bear to be at the cottage we shared for so many years – I kept expecting him to walk up the garden path.

‘I still can’t quite believe it. It just seems so absurd that compost can kill you.’