The World Health Organization is urging governments to focus antibiotic research efforts on a list of urgent bacterial threats, topped by several increasingly powerful superbugs that cause hospital-based infections and other potentially deadly conditions.
The WHO listed the top 20 bacteria that it believes are most harmful to human health, other than mycobacteria such as Mycobacterium tuberculosis, which causes tuberculosis. The germ was not included in the list because it’s generally accepted to be the most urgent priority for new antibiotic research and development, Marie-Paule Kieny, PhD, a WHO assistant director, said at a press conference.
The priority list is needed because the antibiotic pipeline is “practically dry,” thanks to scientific research challenges and a lack of financial incentives, according to Dr. Kieny. “Antibiotics are generally used for the short term, unlike therapies for chronic diseases, which bring in much higher returns on investment,” she said. The list “is intended to signal to the scientific community and the pharmaceutical industry the areas they should focus on to address urgent public health threats.”
MacXever/Thinkstock
The WHO list begins with Priority 1/“Critical” pathogens that it believes most urgently need to be targeted through antibiotic research and development: Acinetobacter baumannii, carbapenem-resistant; Pseudomonas aeruginosa, carbapenem-resistant; and Enterobacteriaceae (including Klebsiella pneumonia, Escherichia coli, Enterobacter spp., Serratia spp., Proteus spp., Providencia spp., and Morganella spp.), carbapenem-resistant, extended-spectrum beta-lactamase–producing.
“These bacteria are responsible for severe infections and high mortality rates, mostly in hospitalized patients, transplant recipients, those receiving chemotherapy, or patients in intensive care units,” Dr. Kieny said. “While these bacteria are not widespread and do not generally affect healthy individuals, the burden for patients and society is now alarming – and new, effective therapies are imperative.”
Priority 2/”High” pathogens are Enterococcus faecium, vancomycin-resistant; Staphylococcus aureus, methicillin-resistant, vancomycin intermediate and resistant; Helicobacter pylori, clarithromycin-resistant; Campylobacter, fluoroquinolone-resistant; Salmonella spp., fluoroquinolone-resistant; Neisseria gonorrhoeae, third-generation cephalosporin-resistant and fluoroquinolone-resistant.
Pathogens in this category can infect healthy individuals, Dr. Kieny noted. “These infections, although not associated with significant mortality, have a dramatic health and economic impact on communities and, in particular, in low-income countries.”
Priority 3/”Medium” pathogens are Streptococcus pneumoniae, penicillin–non-susceptible; Haemophilus influenzae, ampicillin-resistant; and Shigella spp., fluoroquinolone-resistant.
These pathogens “represent a threat because of increasing resistance but still have some effective antibiotic options available,” Dr. Kieny said.
According to a statement provided by the WHO, the priority list doesn’t include streptococcus A and B or chlamydia, because resistance hasn’t reached the level of a public health threat.
One goal of the list is to focus attention on the development of small-market, gram-negative drugs that combat hospital-based infections, explained Nicola Magrini, MD, a WHO scientist who also spoke at the press conference.
Over the last decade, he said, the pipeline has instead focused more on gram-positive agents – mostly linked to beta-lactamase – that have wider market potential and generate less resistance.
“From a clinical point of view, these multidrug-resistant gram-negative clinical trials are very difficult and expensive to do, more than for gram-positive,” noted Evelina Tacconelli, MD, PhD, a contributor to the WHO report. “Because when we talk about gram-negative, we need to cover multiple pathogens and not just one or two, as in the case of gram-positive.”
Dr. Magrini said he couldn’t provide estimates about how many people worldwide are affected by the listed pathogens. However, he said a full report with numbers will be released by June.
It does appear that patients with severe infection from antibiotic-resistant germs face a mortality rate of up to 60%, while extended-spectrum beta-lactamase–positive E. coli accounts for up to 70% of urinary tract infections in many countries, explained Dr. Tacconelli, head of the division of infectious diseases at the University of Tübingen, Germany.
“Even if we don’t know exactly how many,” she said, “we are talking about millions of people affected.”