These 12 superbugs pose the greatest threat to human health

Two rod-shaped carbapenem-resistant Klebsiella pneumonias bacteria are part of the family of germs known as Enterobacteriaceae. Photo / National Institute of Allergy and Infectious Diseases

The World Health Organisation announced its first list of antibiotic-resistant "priority pathogens" today, detailing 12 families of bacteria that agency experts say pose the greatest threat to human health and kill millions of people every year.

The list is divided into three categories, prioritised by the urgency of the need for new antibiotics. The purpose is to guide and promote research and development of new drugs, officials said.

Most of the pathogens are among the nearly two dozen antibiotic-resistant microbes that the US Centres for Disease Control and Prevention warned in a 2013 report could cause potentially catastrophic consequences if the United States didn't act quickly to combat the growing threat of antibiotic-resistant infections.

"This list is not meant to scare people about new superbugs," said Marie-Paul Kieny, an assistant director-general at WHO. "It's intended to signal research and development priorities to address urgent public health threats."

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.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. While these pathogens are not widespread, "the burden for society is now alarming," she said.

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 healthcare workers or by equipment that gets contaminated and is not properly cleaned.

WHO's list follows a summit on superbugs that world leaders held last year - only the fourth time they had addressed a health issue at the UN General Assembly.

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. While they're not associated with significant mortality rates, "they have a dramatic health and economic impact, particularly in low-income countries," Kieny said.

Although there has been renewed interest and research investment in antibiotics because of the growing threat that antibiotic resistance poses, much of the work is more focused on antibiotics with a broad range, she said. "We have to focus specifically for a much smaller range of bacteria," specifically targeting the three highest-priority pathogens, Kieny said.

Here is the list from WHO:

Priority 1: Critical

1. Acinetobacter baumannii, carbapenem-resistant 2. Pseudomonas aeruginosa, carbapenem-resistant 3. Enterobacteriaceae, carbapenem-resistant, ESBL-producing

Priority 2: High

4. Enterococcus faecium, vancomycin-resistant 5. Staphylococcus aureus, methicillin-resistant, vancomycin-intermediate and resistant 6. Helicobacter pylori, clarithromycin-resistant 7. Campylobacter spp., fluoroquinolone-resistant 8. Salmonellae, fluoroquinolone-resistant 9. Neisseria gonorrhoeae, cephalosporin-resistant, fluoroquinolone-resistant

Priority 3: Medium

10. Streptococcus pneumoniae, penicillin-non-susceptible 11. Haemophilus influenzae, ampicillin-resistant 12. Shigella spp., fluoroquinolone-resistant