Superbugs that the WHO considers the highest priority are responsible for severe infections and high mortality rates, especially among hospitalised patients in intensive care or using ventilators and blood catheters, as well as among transplant recipients and people undergoing chemotherapy.

Included in this highest-priority group is CRE, or carbapenem-resistant Enterobacteriaceae, which US health officials have dubbed “nightmare bacteria.” In some instances, it kills up to 50 per cent of patients who become infected. An elderly Nevada woman who died last year contracted an infection caused by CRE that was resistant to all 26 antibiotics available in the United States.

Also included in this critical group is Acinetobacter baumannii; the infections tied to it typically occur in ICUs and settings with very sick patients. Also listed is Pseudomonas aeruginosa, which can be spread on the hands of health-care workers or by equipment that gets contaminated and is not properly cleaned. The list’s second and third tiers - the high and medium priority categories - cover bacteria that cause more common diseases, such as gonorrhea and food poisoning caused by salmonella.

In the United States, antibiotic-resistant infections kill an estimated 23,000 Americans each year, according to the US Centres for Disease Control and Prevention. Global estimates are difficult because there is no uniform way to include antimicrobial resistance in causes of death. But experts say that drug-resistant infections, especially those caused by the WHO’s highest-priority pathogens, double or triple the risk of death.