Researchers can track precisely where typhoid cases are highest by monitoring environmental samples for viruses called bacteriophages that specifically infect the bacteria that cause typhoid. Senjuti Saha of the Bangladesh Child Health Research Foundation and her colleagues report these findings in a new study published February 15 in the open-access journal PLOS Neglected Tropical Diseases.
Typhoid fever is a common infection in many low- and middle-income countries and causes approximately 135,000 deaths and 14 million infections worldwide each year. The World Health Organization has prequalified two typhoid vaccines, but for policymakers to plan effective vaccination strategies, they need accurate, high-resolution estimates of where the burden is greatest.
Traditionally, people have grown the bacteria that causes typhoid fever from blood samples to determine where the infection is most common, but in the new paper, the researchers tested a more cost-effective surveillance approach. They analyzed environmental water samples from wastewater and other locations for bacteriophages specific to the waterborne pathogen that causes typhoid fever, Salmonella Typhi.
The team analyzed 303 water samples from two locations in Bangladesh: the urban capital, Dhaka, and a rural district, Mirzapur. They found that Salmonella Typhi-specific bacteriophages were present in 31% of environmental samples in Dhaka, compared to only 3% of samples from Mirzapur. This corresponds to the results of more than 8,400 blood cultures, in which 5% of the cultures in Dhaka and 0.05% of those in Mirzapur were positive.
The new results suggest that the detection of Salmonella Typhi-specific bacteriophages may be a rapid environmental surveillance method that could help decision makers understand the presence of typhoid fever in the community. The researchers propose that environmental monitoring of bacteriophages could be a simple, cost-effective and scalable tool to aid policy decisions on typhoid fever control.
The authors add: “Searching for bacteriophages in wastewater is a low-cost method to identify typhoid hotspots without the need to perform expensive blood cultures on thousands of people.”