E-cigs could carry bacteria that cause lung problems as experts warn there are growing concerns abou

E-cigarettes may be contaminated with bacteria and fungi linked to lung disease, research suggests.

Scientists who tested 75 single-use cartridges and refill liquids found signs of harmful bugs in just over a quarter.

Meanwhile glucan – a sugary molecule found in most fungi – was detected in 81 per cent of the products.

Exposure to the toxins has been associated with a range of health problems including asthma, reduced lung function and inflammation, the researchers say.

A team from the Harvard TH Chan School of Public Health studied e-cigarette – or 'vaping' – products from some of the top-selling brands in the US.

They identified a microbial 'endotoxin' from 'gram negative' bacteria, which have a tough outer coating that makes them especially resistant to antibiotics. 

Professor David Christiani, who led the team, said: 'Airborne gram negative bacterial endotoxin and fungal-derived glucans have been shown to cause acute and chronic respiratory effects in occupational and environmental settings. 

'Finding these toxins in e-cigarette products adds to the growing concerns about the potential for adverse respiratory effects in users.'
The findings are reported in the journal Environmental Health Perspectives. It is thought that cotton wicks used in e-cigarette cartridges may be a potential source of contamination.
 

Glucan was significantly more abundant in tobacco and menthol-flavoured products, and three times more concentrated in cartridges than in e-liquids.

Co-author Dr Mi-Sun Lee said: 'In addition to inhaling harmful chemicals, e-cig users could also be exposed to biological contaminants like endotoxin and glucan.

'These new findings should be considered when developing regulatory policies for e-cigarettes.'

The study comes after a British expert accused Public Health England of ignoring mounting evidence about the harmful effects of e-cigarettes.

Professor Martin McKee, from the London School of Hygiene and Tropical Medicine, claimed the UK was 'out of step' with other countries when it came to messages about vaping safety.

He argued that e-cigarettes should not be actively promoted as a stop- smoking aid without knowing more about the effects of inhaling nicotine and flavouring chemicals.

He said: 'When we look at the evidence we do have, there's enough grounds for serious concerns.'

PHE has campaigned for smokers to switch to e-cigarettes on the basis that they are 95 per cent less harmful than tobacco products – a figure disputed by Professor McKee. 

Professor John Newton, director of health improvement at PHE, said there was widespread agreement between experts that vaping is 'far less harmful than smoking'.

Last year in the US, more than three million secondary-school students were believed to have been using e-cigarettes - up from 220,000 in 2011, according to the scientists. 

Previous research from Harvard has suggested chemicals linked to severe lung disease are present in common e-cigarette flavour additives.