MONDAY, May 11, 2015 (HealthDay News) -- An antibiotic-resistant strain of the bacteria that causes typhoid fever has spread to many countries and reached epidemic levels in Africa, a new study warns.

The strain, H58, emerged in South Asia between 25 and 30 years ago and has slowly grown to become one of the predominant forms of the bacteria Salmonella Typhi, said study author Vanessa Wong, a microbiologist at the University of Cambridge in England.

"This multidrug-resistant strain, H58, is resistant to a number of first-line antibiotics used to treat the disease and is continuing to evolve and acquire new mutations to newer drugs," Wong said.

Typhoid presents no direct threat to people living in the United States, where clean water supplies and good sanitation prevent exposure to the bacteria, said Dr. Henry Chambers, chief of infectious diseases at San Francisco General Hospital and a professor at the University of California, San Francisco.

But travelers headed to typhoid-ridden parts of Africa and Asia should make sure they receive a vaccination before heading there, Chambers added.

Dr. Wanda Filer, president-elect of the American Academy of Family Physicians, agreed.

"We recommend that people who are traveling to parts of the world where [typhoid] is endemic get the typhoid vaccine," Filer said, adding that the vaccine is 50 percent to 80 percent effective against all strains of typhoid, even those that have become antibiotic-resistant.

Typhoid fever affects between 20 million and 30 million people around the globe each year, the researchers said.

Symptoms include a high, sustained fever, weakness, stomach pains, headache and loss of appetite. As many as 20 percent of patients may die from complications associated with typhoid infection, which can last for weeks or months without proper treatment, according to the U.S. Centers for Disease Control and Prevention.

People contract typhoid when they eat food or drink beverages that have been contaminated with the bacteria, according to the CDC. Someone infected with S. Typhi can pass it on by handling food or drinks. Or, water used for drinking or washing food might become contaminated with sewage containing the bacteria.