An international team of researchers have revealed that an antibiotic-resistant strain of Salmonella typhi — a bacterium that causes typhoid — has surfaced over the past 30 years, and it may represent a previously unrecognized but ongoing epidemic, particularly in Africa.
Worldwide, there are around 21 million cases of typhoid each year and around 200,000 deaths from the disease. Typhoid is primarily contracted by ingesting food or water contaminated with S. typhi, and infection with the bacterium usually causes symptoms within 1-3 weeks after exposure. These may include fever, headache, diarrhea, rose-colored spots on the chest and abdominal pain.
While there are vaccines available for typhoid, their use is not widespread in developing countries. In these countries, typhoid is primarily treated with antibiotics. However, Senior author Dr. Kathryn Holt, of the University of Melbourne in Australia, and colleagues note that a number of strains of S. typhi have become resistant to many first-line antibiotics, compromising treatment of the disease.
Dr. Holt and colleagues collected 1,832 samples of S. typhi from 63 countries between 1992 and 2013 and sequenced the genomes of each one. The researchers found that overall, 47 percent of the S. typhi samples belonged to an antibiotic-resistant strain called H58 - a strain which the researchers now believe is a main driver of antibiotic-resistant typhoid.
According to the authors, the H58 strain has evolved over the past 30 years by acquiring new gene mutations as it travels through regions and populations exposed to new antibiotics. In H58, the antimicrobial resistance genes are becoming a stable part of the genome, which means multiple, antibiotic-resistant typhoid is here to stay.
What is more, the researchers identified evidence of an ongoing epidemic of antibiotic-resistant H58 across Africa. The team says this particular finding emphasizes the need to control antibiotic prescribing practices in this region, which is a likely driver of multidrug-resistant typhoid, as well as an increase in global efforts to contain the spread of the disease worldwide.
Recent reports by the World Health Organization (WHO) reveal that the majority of countries have no national action plan to tackle drug resistance, despite WHO warnings last year that we are heading toward a ‘post-antibiotic era’.