A recent alert sent out by US health officials has highlighted the prevalence of bacteria that cause a potentially fatal stomach bug.
The Centres for Disease Control and Prevention (CDC) warned of the emergence of drug-resistant (XDR) Shigella, which causes about 450,000 infections each year in the US alone.
XDR Shigella is one of a growing number of bacteria that doctors are struggling to control with antibiotics, posing a significant concern for modern medicine.
In November, an eight-year-old girl died in Tunisia after suffering complications caused by the Shigella bacteria. Health officials at the time said 69 children became sick from shigellosis and 11 were admitted to hospital.
What is Shigella and how is it spread?
Four species of Shigella can live in the intestinal tract of infected individuals and cause an unpleasant condition called shigellosis.
These bacteria spread through faeces and are easily caught, with a relatively low dose enough to cause an infection, the World Health Organisation (WHO) says.
They can be passed on through direct person-to-person contact, including sexual contact, and can be picked up from contaminated food and water.
Children under five are most likely to get shigellosis, according to the CDC, with outbreaks often occurring in educational and daycare institutions.
In adults, the CDC says that there has been an increase in Shigella infections among homeless people and those who have been travelling abroad.
While sometimes asymptomatic, infections often lead to diarrhoea, which may contain blood, severe abdominal cramps, vomiting, nausea, headaches and loss of appetite, the WHO reports.
Most people recover within a week but those with a weakened immune system may suffer a severe infection for which antibiotics prove vital.
Dr Bharat Pankhania, a senior consultant in communicable disease control and senior clinical lecturer at the University of Exeter in the UK, said an infection "can flatten you".
"It’s a nasty piece of work," he said. "It gives you profuse water, bloody diarrhoea and if you are elderly, vulnerable or frail, Shigella can be the thing that kills you."
How much of a problem are drug-resistant Shigella and other bacteria?
XDR Shigella accounted for less than 1 per cent of Shigella infections in the US from 2015 to 2019, but in the past three years there has been a steep rise in numbers.
Last year about 5 per cent of Shigella infections in the US involved XDR types.
The XDR form is resistant to the antibiotics that kill other types of Shigella, meaning that doctors "have limited antimicrobial treatment options", the CDC said.
This could increase the number of infections that prove fatal.
XDR Shigella reflects wider concerns that antibiotic-resistant bacteria are becoming more common, blamed on the overuse of antibiotics.
"We’re seeing more resistant bacteria and the pace of discovery of new antibiotics hasn’t really kept pace with the rise of resistant organisms," said Dr Andrew Freedman, an infectious diseases specialist at Cardiff University in Wales.
"The concern is there will be infections for which there is no effective treatment if we’re not careful."
Antimicrobial resistance — which includes drug resistance among viruses, fungi and parasites, as well as bacteria — is already blamed for 700,000 deaths a year, a 2019 paper in BMJ Global Health stated, also forecasting the figure could reach 10 million by 2050.
In a hospital setting, antibiotics may be needed to treat post-surgical bacterial infections of various kinds, so if the drugs become less effective, the risks of operations increase.
"If we run out of antibiotics, we won’t be able to do surgery. Then what?" said Dr Pankhania, describing the rise in antibiotic resistance in bacteria as "a huge, huge, concern".
"Your knee replacement, your hip replacement, your gall bladder removal and heart surgery [could be threatened]."
What can be done about overuse of antibiotics?
A big concern is that on farms, especially intensive operations, animals are routinely given antibiotics to prevent disease outbreaks and improve growth.
According to a 2020 study by scientists in Europe and India, two thirds of antibiotic use involves farm animals, especially poultry and pigs.
"The routine use of antimicrobials fuels the development of antimicrobial resistance, a growing threat for the health of humans and animals," the researchers wrote in the health journal Antibiotics.
Dr Pankhania said that the over-use of antibiotics on farms was a particular issue in the US, and called on "all countries all over the world [to] wake up and take action".
Early last year, the European Union banned the routine administration of antibiotics on farms, with the drugs only allowed to be given to individual sick animals, but regulations in many other parts of the world are looser.
More careful use of antibiotics to treat humans, something known as antibiotic stewardship, is also important, according to Dr Freedman.
"[This means] to only use antibiotics when indicated and to use as narrow spectrum as possible rather than potent antibiotics that have a broad spectrum," he said.
He also said antibiotics should not be given to individuals with viral infections, which sometimes happens even though antibiotics are ineffective against viruses.
Concerns are regularly voiced about the lack of new antibiotics. Dr Freedman said the cost of developing an antibiotic was extremely high but the likely financial returns were relatively modest, so pharmaceutical companies should be offered incentives to carry out the research needed.