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Study finds 80% of cholera infections spread among household members in Dhaka

  • Published at 11:25 am June 26th, 2018

The researchers sequenced the genomes of all the samples to find out how the cholera strains from each person were related, and compared them with strains from other parts of the globe

Nearly 80% of cholera infections were contracted within five days from a household member, a new genomic study finds

Transmission of cholera has been tracked at the household level across Dhaka – a city with a “hyper-endemic” level of the disease – for the first time. 

Researchers from the International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b) and the Wellcome Sanger Institute, along with other collaborators, found that nearly 80% of the cholera transmission in Dhaka occurred between people who shared a household.

The results of the large-scale study published on Monday in Nature Genetics could be used by public health officials to improve cholera control strategies. Preventing the chain of transmission within households in high-burden areas could have a huge impact on reducing the number of cholera cases worldwide.

Dhaka experiences two seasonal outbreaks of cholera each year, and is considered hyper-endemic for the disease. 

To understand how cholera outbreaks sweep through the population, and highlight the best control strategies, the researchers tracked cholera strains at a local level – from people within households who shared a cooking pot and ate together.

Between 2002 and 2005, samples were taken from cholera patients admitted to the Dhaka hospital of icddr,b. Over a surveillance period of three weeks, follow-up samples were taken from other members in the same household of each cholera patient. In total, 303 Vibrio Cholerae samples were collected from 224 individuals across 103 households.

The researchers sequenced the genomes of all the samples to find out how the cholera strains from each person were related, and compared them with strains from other parts of the globe. They found that nearly 80% of the secondary infections were linked to the first case in that household (within the first five days from that person falling ill). This meant that once cholera entered the household it was spreading between household members rather than repeatedly infecting from outside, within this critical time period. This revealed that household control measures are vitally important in stopping the spread of cholera. 

"Using genomics, we found that cholera is easily transmitted within the household. Preventing this spread within the household could enormously reduce cholera outbreaks, and highlights the need for prioritizing local control strategies. This could have a huge impact not only on individual households, but the entire region,” said Daryl Domman, first author of the Wellcome Sanger Institute.

Reducing people’s exposure to Vibrio Cholera at the household level would help to break the chain of transmission of the disease. Local interventions, including better sanitation and hygiene, water chlorination, and vaccinating household members could help reduce the spread of cholera.

Professor Nick Thomson, co-lead author of the Wellcome Sanger Institute and London School of Hygiene and Tropical Medicine said, “Whereas our previous studies have tracked cholera at the global level, here we look at households in a region at high risk of seasonal cholera outbreaks. Our fine-scale genomic data can help identify which control strategies could have the most impact, and we provide genetic tools to measure the effectiveness of household and local interventions in reducing outbreaks." 

Dr Firdausi Qadri, co-lead author of icddr,b said vaccination, together with WASH interventions (improved water, sanitation and hygiene) are critical for the prevention and control of the spread of cholera.

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