(CNN) Over 3 million surgeries and cancer treatments could become deadly in England without working antibiotics, Public Health England said.
Based on new data published Tuesday, the health body said common procedures including caesarean sections and hip replacements could carry greater risks if antibiotic resistance and shortages of the drugs continue to grow.
Antibiotics are used to prevent bacterial infections related to a range of medical procedures, such as surgery, but overusing them can lead to the bacteria becoming resistant.
Cancer patients are also more vulnerable as their cancers and treatments, such as chemotherapy, weaken their immune system and in turn their ability to fight infections.
Antibiotic-resistant blood stream infections rose by 35% between 2013 and 2017 in England, from 12,250 to more than 16,500, according to the report. The most common cause of bloodstream infections was E.coli. Of these, 41% were resistant to the most common antibiotic used to treat infections in hospital, co-amoxiclav.
PHE's research found that 38% of people continued to expect antibiotics to be prescribed when they visited GP's offices or NHS walk-in centers in 2017, for common illnesses such as a cough, flu or a throat, ear, sinus or chest infection.
"Taking antibiotics just in case may seem like a harmless act but it can have grave consequences for you and your family's health in future," said Paul Cosford, medical director at Public Health England.
The agency has re-launched its "Keep Antibiotics Working" campaign to raise awareness of the risks of overusing antibiotics.
"Antibiotics are an essential part of modern medicine, keeping people safe from infection when they are at their most vulnerable," added Cosford.
"It's concerning that, in the not too distant future, we may see more cancer patients, mothers who've had caesareans and patients who've had other surgery facing life threatening situations if antibiotics fail to ward off infections," Cosford said.
The World Health Organization has warned that the speed of increasing antibiotic resistance will outpace the process of developing new drugs.
Last year, a group of British researchers suggested that doctors stop advising patients to complete their course of antibiotics, as this could further increase the development of resistance. (The Royal College of General Practitioners, a network of more than 52,000 family doctors in the UK, urged caution about that advice, and its chairwoman said the public should continue to "complete the course" until more is known.)
The new report found that antibiotic prescribing reduced by 5% between 2012 and 2016, though regional variations were seen, and by 13% in the GP setting.
"The UK has made great efforts in recent years to reduce prescribing rates of antibiotics, however there continues to be a real need to preserve the drugs we have so that they remain effective for those who really need them," said Sally Davies, chief medical officer for England.
"The evidence is clear that without swift action to reduce infections, we are at risk of putting medicine back in the dark ages -- to an age where common procedures we take for granted could become too dangerous to perform and treatable conditions become life threatening," she added.
The campaign is a "great start," Rebecca Glover, research fellow in antibiotic resistance at London School of Hygiene & Tropical Medicine, told CNN.
But she noted: "We must be careful not to place the blame for antibiotic prescribing on patients, who may be responding to increased financial constraints on GP services, shorter appointment times, and difficulties accessing care. Health professionals and patients are allies, not opponents, in the fight against antibiotic resistance."
The new data is "very much in line with what people in the field have been saying for a while," said Andrew Edwards, a non-clinical lecturer in molecular microbiology at Imperial College London.
"We all recognize that you need antibiotics for infections, but what's maybe not fully appreciated is how many areas of modern medicine are built on antibiotics," he added, noting that cancer treatments and surgeries in particular rely on antibiotics that are "40, 50 or 60 years old and cost pennies."
"It doesn't really matter if we can get better cancer treatments or better surgical techniques, if we lose effective antibiotics," he said. "This isn't an issue that's going to go away."
During operations, bacteria can "form a fortress and encase themselves in sugars and proteins and colonize," which provides a route into the bloodstream, Edwards explained.
A decline in effective antibiotics would explain PHE's finding that antibiotic resistant bloodstream infections are already rising at dramatic rates.
Bloodstream infections accounted for 6.6% of healthcare associated infections in England in 2016, the report found.
The UK government has committed to reducing the number of healthcare-associated gram-negative bloodstream infections by half by 2021. These infections account for some of the most serious pathogens contracted in hospitals.
"We do need new antibiotics ... there's a total lack of investment in the area," Edwards said. "We also need to learn to use what we have more effectively.
"It's easy to point the finger at GPs and say they should prescribe less, but bacterial infections can kill very quickly so decisions have to be made on the spot."
The PHE campaign urges patients not to insist on being prescribed antibiotics, noting that GPs often come under pressure to provide them.
"We need to get to a stage where antibiotics are not seen as a 'catch all' for every illness or a 'just in case' back-up option," Helen Stokes-Lampard, chair of the Royal College of GPs, said. " Patients need to understand that if their doctor doesn't prescribe antibiotics it's because they genuinely believe they are not the most appropriate course of treatment."