What is Shigella? Infections caused by sexual transmission rise

Woman with stomach cramps, to represent Shigella STI. (Getty Images)
Shigella detection is not included in general STI screening kits. (Getty Images)

Ever heard of Shigella? This lesser-known STI has been on the rise in recent years, and coupled with an increase in antibiotic-resistant cases in the UK, it's one to watch out for.

"Many people may know Shigella by its more common historical name: dysentery. Over the past four years, we’ve seen a 24% increase in diagnoses of Shigella," says Dr Bhavini Shah, GP from LloydsPharmacy Online Doctor.

"What is also concerning is the rapid rise in antibiotic-resistant strains of Shigella. There has been a 53% increase in antibiotic resistant Shigella from January to November 2023, with 97 cases being reported, compared to just 9 cases for the whole of 2022."

Antibiotic resistance, also known as antimicrobial resistance (AMR), means the bacteria have developed the ability to resist the action of antibiotics that would otherwise kill them or prevent them from growing. It's the bacteria causing the infection that are resistant to the drugs, not us ourselves. AMR is currently posing a big worldwide health threat, from STIs and UTIs to everyday injuries and infections.

And with Shigella being highly infectious, here's everything you need to know.

Illustration of Enterobacteriaceae bacteria. Individual bacterium are shown as pink rod shapes with multiple hair-like flagella used for motility. The Enterobacteriaceae family contains over a hundred species including Shigella, Klebsiella, Salmonella and Escherichia coli and can be found in animal guts, water and soil. Some Enterobacteriaceae members are animal and plant parasites.
Shigella is a type of infectious bacteria. (Getty Images)

"Shigella is a highly infectious bacteria which commonly causes diarrhoea and vomiting, as well as abdominal pain and fever," says Dr Shah.

So it can be classed as an STI? Dr Lawrence Cunningham, contributing medical expert at UK Care Guide and a retired GP, says, "While Shigella is typically known as a bacterial infection that causes dysentery, primarily spread through contaminated food or water, it can indeed be transmitted sexually."

Expanding on this, Dr Shah explains, "Shigella is caused by bacteria found in faeces. Only a tiny amount needs to get into your mouth to pass it on – for example, from your fingers. It’s often caused by contaminated food but it can also be passed on sexually.

"Sex that may involve contact with faeces is a risk. This includes anal sex, fisting, handling a condom or sex toy used for anal sex, oral sex after anal sex, touching someone’s backside or rimming.

"Someone with Shigella can be infectious for up to a month."

While anyone can get it, both males and females, Dr Cunningham adds, "Personally, I have noticed an increase in the number of cases where patients contracted Shigella through sexual contact, particularly within communities of men who have sex with men."

The exact numbers of Shigella diagnoses may be much lower than those of more common STIs like chlamydia or gonorrhoea, but the "increase in year-on-year cases is very worrying," flags Dr Shah.

The month with the highest number of reported Shigella diagnoses prior to the COVID-19 pandemic was 392 in September 2019, which increased to 485 in September 2023 – representing a 24% increase, according to the UK Health Security Agency (UKHSA).

As explained, many people may know Shigella, or Shigella sonnei, by its more common historical name of dysentery. "The disease is often associated with developing countries or ancient times when sanitation was poor," says Dr Shah.

"In the past, dysentery was most commonly caught by people drinking untreated water that had been contaminated with sewage. While this is no longer the case in the UK, it is still a common source of the disease in countries with poor access to sanitary drinking water. Shigella can also be common among young children."

On the differences in treatment, Dr Cunningham adds, "The NHS say that dysentery often resolves on its own and generally refers to milder forms of the disease, which various issues and not just Shigella can cause.

"Shigella-induced dysentery can be quite severe and, in some cases, requires medical intervention. From what I've observed, untreated Shigella can lead to significant dehydration and may even, in its severest form, become life-threatening. Hence, while some bacterial infections might resolve without treatment, Shigella should be taken seriously, and medical advice should be sought if symptoms persist or worsen."

man at doctors clinic
Early intervention is key in treating Shigella. (Getty Images)

"If you’re experiencing symptoms you should contact your GP or local sexual health clinic. You should explain to them that you may have picked up a gut infection from sex, possibly Shigella. The doctor needs to know this so you get the right tests and treatment," Dr Shah emphasises.

So what tests might be given? "When a patient presents symptoms suggestive of Shigella, such as severe diarrhoea, fever and stomach cramps, the first step is to confirm the diagnosis through specific tests," says Dr Cunningham.

"Typically, this involves stool cultures, which, importantly, are not included in the general STI screening kits that test for conditions like chlamydia, gonorrhoea, HIV and syphilis. Therefore, if there's a suspicion of Shigella, especially in patients with relevant sexual history, it's important to conduct these separate specific tests."

"For most people, the illness gets better on its own after three to seven days. But some people can have a severe illness. If your symptoms are severe or persistent, a GP may prescribe a short course of antibiotics," says Dr Shah.

Dr Cunningham agrees. "Treatment usually involves hydration and, in some cases, antibiotics, depending on the severity and susceptibility of the bacterial strain. In my experience, early intervention can significantly ease symptoms and curb transmission."

As well as visiting your doctor, Dr Shah recommends you also:

  • Abstain from sex until seven days after symptoms end

  • Avoid sharing bedding, towels, or clothing

  • Avoid preparing food for others or sharing cooking utensils

  • Wash your hands often with soap and warm water

"Shigella is also highly contagious so you should try to work from home or take sick leave until at least 48 hours after symptoms cease. This is especially important if your job involves handling food and drink or you work in healthcare as you will need to be given the all clear by a public health official," says Dr Shah.

Shigella can be avoided in the first place with good sexual hygiene. "This involves washing your hands after sex, sanitising sex toys, and using a dental dam if you’re engaging in anal rimming. It is also important to avoid any sort of oral sex after having anal sex," he adds.

"In everyday life, you can easily avoid catching Shigella by washing your hands thoroughly with warm water and soap before you eat and after you use the toilet."

If you have any other symptoms or are worried about your sexual health, visit your local clinic or order a home testing kit. There is no shame in STIs, but it is important to stay on top of your sexual health.

Watch: What is antibiotic resistance?