Air pollution can cause blood poisoning and kidney failure at levels previously thought to be harmless, according to research.

Even low exposure raises the risk of a host of potentially fatal illnesses, a study warns. It adds to evidence there is no safe amount of tiny particles called PM2.5s that are pumped into the atmosphere by traffic and industry.

They can be inhaled deep into the lungs where they irritate the lining and enter the bloodstream.

The World Health Organisation’s air quality guidelines need revising, say the US team.

An analysis identified several new causes of hospital admissions linked to small increases in particulate matter, such as sepsis and kidney failure. Others included urinary tract and skin infections.

This was on top of established ones such as heart and lung conditions, Parkinson’s disease and diabetes.

Lead author Yaguang Wei, a doctoral candidate at Harvard TH Chan School of Public Health, Boston, said: “The study shows the health dangers and economic impacts of air pollution are significantly larger than previously understood.”

It was based on more than 95 million Medicare hospital insurance claims for adults aged 65 or older in the US from 2000 to 2012.

Senior author Professor Joel Schwartz, who heads Wei’s lab, said: “We wanted to shed further light on the risks of exposure to short-term air pollution by searching for links between such pollution and all diseases that are plausible causes of hospitalisations.”

These were classified into 214 groups and compared with 13 years’ worth of hospital admissions records. The researchers used data on PM2.5s from the US Environmental Protection Agency and matched it with the postal codes of participants.

Notably, all of the associations remained consistent even on days when daily PM2.5 levels were below the WHO air quality guideline.

Each 1 μg/m3 (one-millionth of a gram per cubic metre of air) rise in short-term exposure was linked with 5,692 more hospitalisations a year, 32,314 days in the hospital and 634 deaths.

What’s more, this included 2,050 extra admissions and 12,216 days in hospital for diseases not previously connected with PM2.5s, such as sepsis, kidney failure, urinary tract and skin infections.

This remained even when the analysis was restricted to days when the concentration was below the recommended level – suggesting it needs updating.

The newly reported diseases represent around a third of the effect, suggesting current figures for PM2.5 associated illness “might be considerable underestimates”.

The researchers added:”This study discovered several new causes of hospital admissions associated with short-term exposure to PM2.5 and confirmed several already known associations, even at daily PM2.5 concentrations below the current WHO guideline.”

They described the findings, published in The BMJ, as “robust” owing to the large sample size over a long time.

Economically, each 1 μg/m3 in PM2.5s corresponded to $100 million (£78m) in annual inpatient and post-acute care costs, and $6.5 billion in the value of lives lost.

Principal investigator Prof Francesca Dominici, a biostatistician at Harvard Chan School, said: “These results raise awareness of the continued importance of assessing the impact of air pollution exposure.

“The strong evidence of a link between exposure to PM2.5 and many diseases, even at levels below the WHO guideline and, nationally, the National Ambient Air Quality Standards in the US, suggests both sets of guidelines should be reviewed and updated.”

Dr Matthew Loxham, an air pollution toxicologist at the University of Southampton, who was not involved in the study, said knowledge of the health effects of particulate matter “is still lacking in many areas”.

He said: “The harder we look, the more we find. Clearly there is much still to learn but we should not mistake knowledge gaps for paucity of evidence.

“The sooner we act, the sooner the world’s population will reap the benefits.”

Dr Loxham and colleagues, writing in an editorial for the journal, call for more research to uncover new disease associations and explore potential causative mechanisms.

WHO guidelines state that the average annual level for PM2.5s should be 10 μg/ m3.

Currently, the UK subscribes to EU guidelines on air pollution, which are far less strict.

Air pollution accounts for an estimated 4.2 million deaths a year.