In a hard-hitting study of antimicrobial resistance -- when bacteria adapt so that existing drugs no longer curb them -- the UN health agency said the problem was a global emergency.
"Without urgent, coordinated action by many stakeholders, the world is headed for a post-antibiotic era, in which common infections and minor injuries which have been treatable for decades can once again kill," warned Keiji Fukuda, the WHO's assistant director-general for health security.
The unprecedented report gathered data from 114 countries, and focused on seven different bacteria responsible for diseases such as diarrhoea, pneumonia, urinary tract infections and gonorrhoea.
Even so-called "last resort" antibiotics are losing their ability to fight such bacteria, with half of the patients showing resistance in some countries, the report said.
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"The capacity to treat serious infections is really becoming less in all parts of the world," Fukuda said, stressing that "antimicrobial resistance is not a just future issue, ... But very much an issue today."
"We see horrendous rates of antibiotic resistance wherever we look in our field operations," said Jennifer Cohn, an MSF medical director.
Among the report's key findings were the global spread of resistance to carbapenem antibiotics -- the last resort treatment for life-threatening infections caused by the common intestinal bacteria Klebsiella pneumoniae.
Known as K. Pneumoniae, it is a major cause of hospital-acquired infections such as pneumonia and sepsis, often hitting newborns and intensive-care patients.
Resistance to one of the most widely used antibacterial medicines for the treatment of urinary tract infections caused by E. Coli -- fluoroquinolones, is also widespread.