What we still don't know about the UK's E. coli outbreak

At least 37 people have been hospitalised in an E. coli outbreak - with cases expected to rise

At least 37 people have been admitted to hospital in an E. coli outbreak. (PA)
An E. coli outbreak has been linked to food. (PA)

At least 37 people have been hospitalised in an E. coli outbreak, the UK Health Security Agency (UKHSA) has said.

E. coli are a diverse group of bacteria which are normally harmless and live in the intestines of humans and animals. However, some strains produce toxins that can make people very ill, such as Shiga toxin-producing E. coli (STEC) - which all the new cases involve.

People infected with STEC can suffer diarrhoea, and about 50% of cases have bloody diarrhoea. Other symptoms include stomach cramps and fever.

Bacteriologist Prof Nicola Holden said the outbreak “is a concern because it is a serious, notifiable pathogen that can cause severe and sometime fatal disease”.

Here is what we know - and don’t know - about the outbreak.

As well as the 37 hospitalisations, we know there were 113 confirmed STEC cases between 25 May and 4 June.

Of these, 81 were in England, 18 in Wales, 13 in Scotland and one in Northern Ireland, with that person believing they fell ill in England.

The UKHSA said genome sequencing of samples indicated most of these cases are part of a single outbreak.

We know that owing to the “wide geographic spread of cases”, the UKHSA has linked the outbreak to a nationally distributed food item or multiple food items.

Typically, there are about STEC 1,500 cases every year and the number in this outbreak is expected to rise from the current 113.

We also know the age profile of people who have been affected. While this ranges between two and 79, the majority are young adults.

The UKHSA will now be working closely with the food standards agencies of the devolved agencies to identify the source, according to Prof Holden. She also warns that accurately estimating the source is "normally an estimate". That is because food products have often been consumed or destroyed and are no longer present with the contaminating pathogens.

We don't know the exact food item that caused the outbreak. The UKHSA said it is working with public health agencies in Scotland, Northern Ireland and Wales, as well as the Food Standards Agency (FSA) and Food Standards Scotland, to determine the cause.

The agency has also said there is no evidence linking the outbreak to open farms, drinking water or swimming in contaminated sea, lakes or rivers.

And, while the UKHSA has provided a country-by-country breakdown of cases, we don't know which regions have been worst affected.

We also don't know how bad the outbreak will be. Prof Holden said: "There is a dependency on the type of source: the epidemiological curves look different for a perishable product compared to something long-lasting, which may be more prolonged."