The antibiotic-resistant strain of Salmonella typhi, the primary cause of typhoid, emerged within the last 30 years and may represent an ongoing, previously unrecognized epidemic in Africa, reports a study published online this week in Nature Genetics.
Typhoid affects 20-30 million people globally each year. Symptoms include nausea, fever and abdominal pain. Some people infected with the bacteria show no symptoms, but they are still able to transmit the disease. Vaccination and antibiotics can be used to effectively treat many cases of typhoid, but strains of S. typhi that are resistant to antibiotics have emerged since the 1970s.
Vanessa Wong and colleagues sequenced the genomes of 1,832 samples of S. typhi that were collected from 63 countries between 1992 and 2013. They found that 47% belonged to a single strain known as H58, which is resistant to multiple antibiotics. The geographic pattern of antibiotic resistance found in this study reflects the usage of antibiotic drugs in those regions. The researchers found that H58 emerged in South Asia 25-30 years ago and spread to Southeast Asia, Western Asia, East and South Africa, and Fiji. They also found evidence of a recent and unreported wave of H58 transmission in multiple countries in Africa, which may represent an ongoing epidemic.