Researchers found that nearly 80% of all cholera transmissions in Dhaka, Bangladesh, occurred between people who shared a household. With the rise in cholera cases around the world, these findings could potentially impact infection control strategies.
“Dhaka is a megacity that is hyperendemic for cholera and experiences two regular seasonal outbreaks of cholera each year,” Daryl Domman, PhD, a postdoctoral fellow in the infection genomics program at the Wellcome Trust Sanger Institute, and colleagues wrote. “Despite this, a detailed understanding of the diversity of Vibrio cholerae strains circulating in this setting, and their relationships to annual outbreaks, has not yet been obtained.”
Domman and colleagues assessed samples collected from the household contacts of index patients treated at the International Center for Diarrheal Disease Research between 2002 and 2005. These household contacts were defined as those who shared a cooking pot with the infected individual up to 3 days before admission to the center. Samples were collected during a 3-week follow-up period.
Over 100 households were represented by samples from 224 people. The researchers were able to isolate V. cholerae in 45 samples. Using whole-genome sequencing, Domman and colleagues examined and compared 303 strains to assess how they had evolved.
Between 2002 and 2005, the researchers observed six sublineages of the seventh pandemic V. cholerae El Tor (7PET) strain. These strains ran concurrently in Dhaka throughout the study, and included two different serotype O1 Ogawa sublineages (B5 and B6), two O1 Inaba sublineages (B1 and B2) and two O139 serogroup sublineages (B3 and B4).
Of the 79 households from which more than one member was admitted to the center, 23% were attributable to different sublineages, meaning that nearly 80% of infections were related to the first case reported in the household. A significant number of the infections caused by different strains were related to the 7PET lineage. The researchers observed two households in which both 7PET and non-7PET V. cholerae were reported.
Domman and colleagues noted that 42% (n = 94) of household contacts did not develop clinical symptoms during this time, although stool cultures were positive for V. cholerae. According to the researchers, 127 contacts had both diarrhea and a positive culture.
“Preventing the spread [of cholera] within the household could enormously reduce cholera outbreaks and highlights the need for prioritizing local control strategies,” Domman said in a press release. “This could have a huge impact not only on the individual households, but also on the entire region.” – by Katherine Bortz
Disclosures: The authors report no relevant financial disclosures.