To date, decisions about which pathogens to prioritize for research and development (R&D) have been made by individual drug companies, large and small. These decisions tend to be variously influenced by perceived or unmet medical needs, pressure from investors, potential for scientific discovery, availability of technology, and market size, say the WHO.
Dr. Marie-Paule Kieny, assistant director-general for Health Systems and Innovation at the WHO, says that:
“Antibiotic resistance is growing, and we are fast running out of treatment options. If we leave it to market forces alone, the new antibiotics we most urgently need are not going to be developed in time.”
The idea of a priority pathogen list is not new; in 2013, for instance, the Centers for Disease Control and Prevention (CDC) published an antibiotic resistance threat list for the United States. However, this is the first time that a list has been produced by a global health agency from the point of view of threat to worldwide public health.
In a report on how they compiled it, the WHO note that the main objective of the global priority pathogen list is to “guide the prioritization of incentives and funding, help align R&D priorities with public health needs, and support global coordination in the fight against antibiotic-resistant bacteria.”
The problem of growing antimicrobial resistance
Antimicrobial drugs have been used effectively for more than 70 years and have greatly reduced illness and death from infection. However, many of them – such as antibiotics designed to kill disease bacteria – have been used so widely and for so long that the microbes have adapted and become highly drug-resistant.
New mechanisms of drug resistance are emerging and spreading around the world, threatening our ability to treat even common infections. This is resulting in lengthier illnesses, longer hospital stays, costlier and more intensive care, disability, and death.
The new WHO list highlights the particular threat of bacteria that are resistant to more than one drug. These bacteria have not only evolved built-in mechanisms that resist treatment, they can also pass their genetic material to other bacteria so that they, too, become drug-resistant.
Growing antimicrobial resistance is already complicating the treatment of tuberculosis (TB), HIV, and malaria. According to the WHO, there are now 480,000 new cases of multidrug-resistant TB worldwide every year.
Also, without effective drugs to prevent and combat infection, medical procedures such as cancer treatments, organ transplants, diabetes management, cesarian sections, hip replacements, and other major surgical operations, become very high risk.
According to the CDC, at least 2 million people per year in the U.S. become infected with drug-resistant bacteria and around 23,000 people per year die as a direct result of these infections. Many others die from conditions that are complicated by antibiotic-resistant infections.
Critical, high, and medium priority pathogens
The WHO have categorized the 12 bacteria in terms of urgency of need for new drugs: critical, high, and medium priority.
The critical group includes infection-causing bacteria that are resistant to several drugs and pose a particular threat in hospitals and nursing homes, and specifically to patients on ventilators or fitted with blood catheters.
The bacteria in the critical group include: Acinetobacter, Pseudomonas, and some Enterobacteriaceae (including E. coli, Klebsiella, Proteus, and Serratia).
These pathogens can cause severe and often fatal infections, including pneumonia and bloodstream infections.
The high and medium priority groups contain other bacteria that are becoming increasingly resistant to available drugs, and that cause more common infections such as gonorrhoea, food poisoning (caused by salmonella), and Staphylococcal infections (caused by resistant forms of Staphylococcus aureus, such as MRSA).
Drug-resistant strains of the following bacteria are also in the high and medium priority groups: Enterococcus faecium, Helicobacter pylori, Campylobacter species, Streptococcus pneumoniae, Haemophilus influenzae, and Shigella species.
Decision criteria for pathogen inclusion
Researchers from the University of Tübingen in Germany collaborated with the WHO in compiling the list, using criteria and a decision-making method that was vetted by international experts.
The criteria used included: the deadliness of the pathogen; the length of hospitalization they cause; frequency of resistance to antibiotics when spread in the community; ease of spread in animals, from animals to humans, and among humans; how easy it is to prevent infection; how many treatment options are available; and whether new drugs to tackle them are already in development.
The list does not include the bacterium that causes TB because this is already targeted by existing, dedicated programs. Other bacteria – such as Streptococcus A and B and chlamydia – are also excluded because they have low levels of resistance to current drugs and do not pose a significant threat to public health, say the WHO.
Evelina Tacconelli, a professor, head of the division of infectious diseases at Tübingen, and a major contributor to the work, concludes:”New antibiotics targeting this priority list of pathogens will help to reduce deaths due to resistant infections around the world. Waiting any longer will cause further public health problems and dramatically impact on patient care.”
The WHO also point out that new drugs on their own will not solve the problem of antimicrobial resistance. We also need to continue efforts to prevent infection and avoid inappropriate use of existing and future antibiotics, according to MNT.