The study published in the Lancet, which involved the analysis of stool samples from more than 10,000 children in countries across Africa and south Asia, also found that nearly 78% of cases were caused by just six bugs – an insight scientists say could help to tackle the problem.
“It really comes down to just a handful of pathogens that are most important,” said Eric Houpt of the University of Virginia who co-authored the study. “So it is not a hopelessly long list of infections that we can’t do anything about.”
Diarrhoea is the second most common cause of death among children under five after pneumonia, and it has also been linked to stunted growth. It is believed to be caused by infections that spread by contaminated food and waterbetween people, but it has been difficult to pinpoint the cause of each case.
“Diarrhoea in children under five years old remains an enormous public health problem with half a million deaths each year or more, mostly in Africa and south Asia,” said Houpt.
He says the research will galvanise scientists to develop new ways to tackle the pathogens responsible for diarrhoea. “My feeling is that vaccine developments and proper use of antibiotics can lead to a large decrease in childhood diarrhoea over the next 10 to 20 years if we target these six pathogens, while hopefully economic development trickles along,” he said.
Writing in the Lancet, an international team of researchers describe how they re-analysed stool samples collected as part of an earlier multi-year project called the Global Enteric Multicenter Study, which looked at cases of moderate to severe diarrhoea in children under five in seven countries across Africa and south Asia.
The initial results, published three years ago, suggested that 51.5% of cases were down to pathogens, with the findings based on a suite of analytical methods including culturing bacteria. But researchers decided to re-analyse the samples in the light of the recent development of highly sensitive genetic analysis techniques.
The new study analysed samples from 10,608 children, half of whom had diarrhoea and half were unaffected “controls”, in an attempt to unpick the proportion of cases caused by bacteria, viruses and other pathogens, focusing on 32 known to be linked to diarrhoea.
“These [new techniques] get down to lower amounts. We can tell not only what is there for the 32 but how much is there – so they give a quantitative result as well,” said Houpt.
The results reveal that the influence of pathogens has been underestimated, with 89.3% of childhood diarrhoea cases caused by pathogens. Just six, including rotavirus and Cryptosporidium parasites, were responsible for almost 78% of cases.
What’s more, almost 40% of diarrhoeal cases showed evidence of two or more pathogens, suggesting that multiple infections are at play, while even among the apparently healthy controls many children were found to have low levels of infection.
Of the six key pathogens identified, only one – rotavirus – currently has a vaccine available, although vaccines for two of the other pathogens, bacteria known as Shigella and ETEC (a type of E.Coli), are in the pipeline.
Professor Val Curtis, director of the environmental health group at the London School of Hygiene & Tropical Medicine, welcomed the findings, saying the research has demystified the causes of the condition. “It is exciting because we are no longer in the dark ages about diarrhoea,” she said. “We are moving into a new era where we can actually use molecular methods to detect with much more sensitivity the pathogens in stools.”
“Diarrhoeal disease is not sexy. It sounds unpleasant. It has never been the area that people have really, really wanted to put their effort into,” she said. “’We need to talk about shit’ is my campaign slogan.”
By Nicola Davis