An increase in cases of dysentery caused by shigella infection has been identified among men who have sex with men around the UK, according to preliminary findings from a Health Protection Agency (HPA) investigation published last week.

Following two outbreaks of shigella infection among MSM in Greater Manchester and London last year, affecting around 20 men, the HPA put in place ‘enhanced surveillance’ in September 2011 to try and ascertain the extent of the problem across the UK.

Shigella dysentery is often acquired by drinking contaminated water or by eating food washed with contaminated water. In the UK most cases of shigella are associated with foreign travel.

The enhanced surveillance, which ran from September to December 2011, picked up 145 cases of shigella infection, of which 31 were UK acquired. Of these 31 cases, they were predominantly male and just under half reported MSM activity within the previous week. The investigation showed that these men attended regular health checkups and all reported having a casual male partner in the preceding week.

These findings suggest that the UK acquired cases in men who have sex with men may be transmitted through sex or through secondary contact. Although the enhanced surveillance gives an indication of the numbers affected, it does not pick up all of the cases and the HPA believes the current UK outbreak of shigella is considerably larger than this.

As a result of these preliminary findings, the HPA is stressing the need for men who have sex with men to consult their doctor if they have diarrhoea, especially if it is bloody, and for health professionals to be on the alert for possible cases in men who have sex with men.

Dr Isabel Oliver, head of the outbreak control team said: “It’s very unusual to see outbreaks of this illness that are not linked to foreign travel which is why we undertook extra surveillance to try to understand who the disease is affecting and why.

“Our investigation has revealed a strong association between UK acquired shigella and onward transmission in men who have sex with men.

“We also know that the cases are not part of one large outbreak, but are small clusters happening across the country, therefore it is important to be aware of simple precautions to stop the spread of the infection.

“We continue to advise people in these groups to go to their doctor if they have diarrhoea, to see whether they’re infected with shigella. If they do have this illness, avoiding having sex until they’ve made a full recovery will reduce the risk of onward transmission.

“Washing hands thoroughly before preparing and eating food, after going to the toilet and, if having sex, before and afterwards, may also lower the risk of people with this illness spreading it to others. Ingesting even a small number of shigella germs can lead to infection.

“As part of the investigation we also worked with the Terence Higgins Trust and the British Association for Sexual Health and HIV to raise awareness of shigella and its symptoms to men who have sex with men and health professionals.

“Investigations into other risk factors for onward transmission and the possibility of using screening tests to diagnose infection in asymptomatic contacts of cases with shigella dysentery continue.”

The main symptom of shigella is bloody diarrhoea – which should always be investigated by a doctor. People who are diagnosed with this illness can be treated with antibiotics, and most people in this country will make a full recovery and experience no complications.