80pc cholera infections in Dhaka spread within household

• 25% diarrhea patients at icddr,b Dhaka had cholera (April-June '18)

• 80% infections occur through household members

• 3,000,000-5,000,000 suffer from cholera each year globally 

• 1,20,000 of them die from the disease

Around 80 percent of cholera infections in Dhaka contract through members who share a household, cooking pot and eat together, according to a new study published in US-based science journal Nature Genetics on Monday.

“Once cholera entered the household, it was spreading between household members, rather than repeatedly coming in from outside, within this critical time period [in first five days],” said the study conducted by icddr,b, Wellcome Sanger Institute, UK, and other collaborators.

The findings suggest that household control measures, including better sanitation and hygiene, water chlorination and vaccinating household members could help reduce cholera spread, researchers said.

The findings are important as Dhaka, a megacity in Bangladesh, experiences two seasonal outbreaks of cholera each year – one in April-May and the other in August-September.  It is considered hyper-endemic for the disease, icddr,b said.

There is no prevalent data of cholera in Dhaka. However, on an average 700 diarrhoea patients who took admission at the icddr,b's Dhaka hospital between April and mid-June. Of them, around 25 percent had cholera infection, an icddr,b spokesman told The Daily Star. 

Globally, around 1.4 billion people are at risk in endemic countries, with an estimated 3 to 5 million new cases each year. The disease causes up to 120,000 deaths per year globally, it added.

To understand the outbreaks and highlight control strategies, researchers tracked cholera strains at local level -- from people within households.

Researchers collected samples from cholera patients admitted to Dhaka hospital of icddr,b between 2002 and 2005. Over a period of three weeks, follow-up samples were taken from other members of the same household as patients. Some 303 Vibrio cholerae samples were collected from 224 individuals across 103 households.

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

They found nearly 80 percent of secondary infections being linked to the first case in that household.

“We found that cholera is easily transmitted within the household. Preventing this spread could enormously reduce cholera outbreaks,” said Dr Daryl Domman, first author from the Wellcome Sanger Institute.

Reducing people's exposure to Vibrio cholera at household levels would help break the chain of the disease's transmission, Domman said. 

Dr Firdausi Qadri, co-lead author from icddr,b said, “Vaccination together with WASH interventions -- improved water, sanitation and hygiene -- are critical in prevention and control of the spread of cholera.”