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Drug-resistant bacteria killed nearly 1.3 million people in 2019, scientists have estimated - more than either HIV or malaria.
Researchers also estimated that antibiotic-resistant bacterial infections played a role in 4.95 million deaths in the same year.
The results of the study - which was funded by the British government and the Bill & Melinda Gates Foundation - were published in the peer-reviewed medical journal The Lancet on Wednesday.
The WHO has described antibiotic resistance as "one of the biggest threats to global health, food security and development today," and said that although the phenomenon occurs naturally, antibiotic abuse in humans and animals accelerates the process.
Antibiotics are sometimes needed to treat or prevent bacterial infections. However, the overuse and misuse of antibiotics - such as in the treatment of viral infections such as colds, which they are not effective against - has helped some bacteria develop into becoming resistant to them.
This resistance threatens our ability to treat common diseases, leading to higher medical costs, longer hospital stays, and increased mortality. According to the U.S. Centers for Disease Control and Prevention, more than 2.8 million antibiotic-resistant infections occur in the United States each year, with more than 35,000 people dying as a result.
An increasing number of diseases, including pneumonia, tuberculosis and gonorrhea, are becoming more difficult to treat as antibiotics become a less effective tool against the bacteria that cause them.
'Major global health threat'
The authors of the research paper describe bacterial antimicrobial resistance (AMR) as "one of the leading public health threats of the 21st century," adding that their study presented the first global estimates of the burden it added to populations worldwide.
The study looked at 471 million individual records from 204 countries and territories and analyzed data from existing studies, hospitals and other sources. Its estimates were based on the number of deaths due to and associated with bacterial AMR for 23 pathogens (disease-causing organisms) and 88 pathogen-drug combinations.
Lower respiratory tract infections such as pneumonia, which were responsible for 400,000 deaths, were the "most contagious infectious syndrome" related to bacterial AMR, researchers said. Bloodstream infections and intra-abdominal infections were the second most prevalent drug-resistant diseases leading to death in 2019. Together, these three syndromes accounted for almost 80% of the deaths attributable to AMR.
E.coli and MRSA
E. coli and MRSA (methicillin-resistant staphylococcus aureus) were among the drug-resistant bacteria that led to the most deaths, the study found. So-called "superbug" MRSA directly accounted for more than 100,000 deaths during the analysis period, researchers found.
The six pathogens identified in the study as the cause of most deaths from AMR have been identified by the WHO as priority pathogens, researchers said.
Globally, 16.4 deaths out of every 100,000 could be attributed to drug-resistant bacteria in 2019, according to the study. In sub-Saharan Africa, where the AMR accounted for the highest death rate in the world, this rate rose to 27.3 per capita. 100,000 deaths.
Meanwhile, deaths associated with, but not directly caused by, bacterial AMR accounted for 64 out of every 100,000 deaths in 2019, researchers said.
"Our results clearly show that drug resistance in each of these leading pathogens is a major global health threat that justifies more awareness, funding, capacity building, research and development and pathogen-specific prioritization from the wider global health community," the researchers say. said in their newspaper.
Antibiotic investment 'important'
The study's authors called for stringent intervention strategies, many of which were linked to antibiotic use, to address the threat posed by drug-resistant bacteria. Proposals made in the paper included reducing human exposure to antibiotics in meat, minimizing unnecessary use of antibiotics - for example to treat viral infections - and preventing the need for antibiotics through vaccination programs and vaccine development.
Researchers also said it was "significant" to sustain investment in the development of new antibiotics.
"In the last couple of decades, investment has been small compared to those in other public health issues with similar or lesser impact," they said.
The study authors acknowledged that their research had some limitations, including sparse data from low- and middle-income countries, which could lead to an underestimation of the AMR burden in certain regions.
"Efforts to build laboratory infrastructure are crucial to addressing the large and universal burden of AMR by improving the handling of individual patients and the quality of data in local and global monitoring," the report's authors said.
"Improved infrastructure will also expand AMR research in the future to evaluate the indirect effects of AMR ... Identifying strategies that can work to reduce the burden of bacterial AMR is an urgent priority."