Blood samples to help track recent cholera infection

icddr,b researchers and US collaborators have developed a method to use blood samples to identify individuals recently infected with cholera in order to improve cholera surveillance.

Six blood serum markers identified in cholera patients have been shown to confirm recent cholera infection in individuals with 93 percent accuracy, using machine learning methods, according to the study conducted by researchers from Johns Hopkins Bloomberg School of Public Health, University of Utah, Massachusetts General Hospital, Harvard Medical School and Harvard T.H. Chan School of Public Health and icddr,b.

Appropriately tracking cholera infection is essential to achieve an ambitious goal like End Cholera 2030. Photo: GMB Akash / icddr,b

Traditional cholera surveillance is based almost entirely on clinical reporting of watery diarrhea and a few laboratory-confirmed cases. While only a few develop severe symptoms, many do not seek medical care at all and the traditional system does not accurately represent the exact scenario.

"Our work shows that a drop of blood likely contains enough information to tell if someone was infected with the bacteria in the past year," says Dr Andrew Azman, assistant scientist in epidemiology at Johns Hopkins Bloomberg School of Public Health and lead author on the study published in Science Translational Medicine.

"It gives us another way to track cholera without having to fully rely on clinical data from the less than ideal health surveillance systems often available in cholera-affected countries," he adds.

Dr Daniel Leung, MD, MSc, an assistant professor of infectious diseases at University of Utah Health and co-author of the study, observes that establishing such a serosurveillance method overcomes many of the shortcomings of traditional surveillance approaches.

“It provides a new way to track the spread of cholera in short-term outbreaks as well as assess long-term burden of cholera across different populations," adds Dr Leung.

Appropriately tracking cholera is important since an infected person, even while without symptoms, sheds the bacteria for up to a week after infection, sometimes passing the disease to others, typically through contaminated water.

Dr Firdausi Qadri, senior scientist at icddr,b infectious diseases division expects that researchers will now be able to predict the exposure status of an endemic population, after studying cholera immune responses for several decades to understand infection, and plan strategies to prevent active or passive disease prevention.

"We are working on simpler sampling methods to further optimise procedures for analysing large populations for antibody responses,” she adds.

The study was supported by the Bill and Melinda Gates foundation and the National Institutes of Health.


Help Ending Cholera: 2030

Cholera continues claims over 100,000 lives yearly around the world despite efforts to improve the availability of safe water and adequate sanitation.

Poor water, sanitation and hygiene keep challenging end cholera initiatives. Photo: GMB Akash / icddr,b

To alleviate such suffering, World Health Organization (WHO) Global Task Force for Cholera Control (GTFCC) set a goal to eliminate cholera as a public health threat by 2030.

New methods such as appropriately tracking cholera infection using serum markers are essential to count cholera cases to achieve such an ambitious goal.

The researchers tested the method by conducting simulations of cholera transmission and they were able to estimate the number of infections in hypothetical settings where cholera is common, and regions where it is episodic.

These results help illustrate how this approach can be put to use in public health practice.

While this method is a positive step forward, it is based on data from a region where cholera is common, and validated by a small number of patients during challenge experiments in non-endemic regions.

In addition, the method cannot differentiate between someone who has been infected with cholera or vaccinated against the disease. Currently, the team is working on validating the method in Haiti, where cholera fluctuates annually.

"Applying routine serosurveys like this method in cholera hotspots or after epidemics could help us better understand the true burden of this disease across populations, time, and space," says Leung.