Stool culture may underperform in detecting new surges of cholera
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Key takeaways:
- Stool culture “performed worse than would be expected” in diagnosing cholera during a waning outbreak in Haiti.
- Other methods may be useful in this context to identify new surges of the gastrointestinal illness.
Stool culture “performed worse than would be expected” in diagnosing cholera during a period of waning cases in Haiti compared with PCR testing, according to the results of a small study.
“This finding is important because, as cholera cases wane over the course of a big outbreak, rigorous laboratory-based surveillance must correspondingly increase to identify ongoing transmission, detect outbreaks early, and allow public health officials to be on alert for new surges,” wrote Louise C. Ivers, MD, MPH, director of the Harvard Global Health Institute and executive director of the Center for Global Health at Massachusetts General Hospital, and colleagues.
Image: Adobe Stock.
Historically, stool culture has been considered the “gold standard” for diagnosing cholera, with PCR also recognized as a reliable method, albeit more difficult when investigating outbreaks because it is more expensive and requires skilled staff, according to Ivers and colleagues.
Treating people with cholera does not require lab confirmation, even with multiple patients, because the methods of treating diarrhea and dehydration will not change regardless of diagnosis, according to Ivers.
“Cholera happens in places where infrastructure is broken down or infrastructure is weak, including in Haiti, and places like Yemen and Malawi, and other countries where structures are not there to prevent diarrheal disease,” Ivers told Healio.
“So, at the same time as the disease is happening in places that are often impoverished or in conflict, those are the exact same places where a laboratory infrastructure is not the most robust — and that includes Haiti,” Ivers said.
For almost a decade, Haiti battled a large and deadly cholera outbreak that began after a devastating 2010 earthquake and infected 820,000 people, killing nearly 9,800, according to WHO.
Haiti was declared free of cholera in early 2022 after 3 years without a case but has experienced a resurgence of the disease since last fall, with more than 13,600 suspected cases and 283 deaths reported between October and December alone.
For their study, Ivers and colleagues examined whether cholera had been cleared from Haiti or was still circulating at lower, harder-to detect-rates. They enrolled 60 participants — 28 male and 32 female — aged 7 months to 80 years with acute watery diarrhea who met the clinical definition of cholera between September 2018 and March 2019.
Among 43 patients with complete clinical information, 51.16% had moderate dehydration and 23.26% had severe dehydration.
Although stool culture was used, Ivers said the researchers added PCR testing to more rigorously look for cholera cases that may have been missed during the period of low case rates in Haiti. They stored stool samples on filter paper for transportation to Boston within 14 days of collection — unless that was not possible, in which case the samples were frozen — and tested them using PCR.
They were surprised to find that stool culture was less reliable for identifying cholera — it was 33.3% sensitive and 97.4% specific for detecting the presence of cholera when PCR was considered the gold standard.
Ivers cautioned that the results were from one small study and do not represent “a major blow-up of things that we know about cholera,” but suggest that adding novel techniques to cholera surveillance could be useful.
“I think that what we’re really learning is that when we want to find cholera and understand where cholera is happening, which diarrheal disease is cholera versus other types of pathogens, we’re going to need to embrace molecular tools like PCR and understand when to use them from a research perspective, when to use them from a screening perspective and when to use them from a surveillance perspective,” she said.
References:
- Guillaume Y, et al. Open Forum Infect Dis 2023;doi:10.1093/ofid/ofad301.
- WHO. Cholera – Haiti. https://www.who.int/emergencies/disease-outbreak-news/item/2022-DON427. Published Dec. 13, 2022. Accessed June 13, 2023.
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