Did You Ever Want to Know What Bugs Were Actually in Diarrhoea?

Maybe not, but the CLAHRC WM Director is fascinated by stool and its contents. He shares this scatological interest with the 51-odd authors of the Global Multicenter Enteric Study who collected stool specimens from 9,439 children with diarrhoea, and no less than 13,129 control children.[1] Then they used quantitative PCR (polymerase chain reaction) to analyse the samples. Children in low- and middle-income countries (LMICs) often harbour asymptomatic enteropathogens. However, there was evidence that the level of pathogen-derived nucleic acid could distinguish between infection and asymptomatic shedding.

The authors found:

  1. Types of organism that were highly prevalent with strong quantity-dependent associations with symptoms – these include rota-virus, adenovirus 40/41, Shigella spp, Cryptosporidium spp, and some types of E. coli.
  2. Organisms like Salmonella spp, norovirus, V.  cholerae, and E. histolytica that showed strong quantitative associations with diarrhoea, but which had low prevalence.
  3. Organisms, such as various Campylobacter spp and other types of E. coli that were highly prevalent, but only moderately associated with diarrhoea – they are frequently found in the stool of asymptomatic people.
  4. Organisms that were only associated with diarrhoea in specific contexts, such as Aeromonas spp and enteroaggregative E. coli.
  5. Organisms that showed no association with diarrhoea, such as T. trichiura and A. duodenale.

A microbiological cause for diarrhoea could be found in 90% of cases when quantitative PCR was used, while a cause was found in only half of cases of diarrhoea using traditional methods. This is because some organisms, such as Shigella spp, are difficult to grow in culture. It had previously been thought that bloody diarrhoea is the hallmark of Shigella infection, but this study shows that many cases are associated with watery diarrhoea, rather than dysentery, at least in children. Future development of rapid quantitative assays should help identify cases that need antibiotics, and gene sequencing should also provide evidence on antibiotic resistance. Most important, we need improved sanitation to get rid of this lethal disease.

— Richard Lilford, CLAHRC WM Director


  1. Liu J, Platts-Millsa JA, Juma J, et al. Use of quantitative molecular diagnostic methods to identify causes of diarrhoea in children: a reanalysis of the GEMS case-control study. Lancet. 2016; 388: 1291-301.

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