Cases of a gastro superbug are rising in Victoria, prompting a warning from the state's public health chief.

Outgoing Victorian chief health officer Brett Sutton on Wednesday issued an alert for clinicians and the public over increasing antibiotic-resistant shigella bacteria infections, also known as shigellosis.

Shigellosis is a bowel infection and can lead to acute diarrhoea, fever, nausea, vomiting and abdominal cramps.

It is highly contagious and can be transmitted through sexual contact.

"Symptoms usually develop one to three days following exposure but can occur as early as 12 hours to as late as one week afterwards in some cases," Prof Sutton's alert warned.

"Cases remain infectious while the shigella bacteria continue to be shed in faeces. This can last for up to four weeks after symptoms resolve."

Many of the antibiotic-resistant Victorian cases have been identified among men who have had recent sexual contact with other men, while others involved returned travellers.

Health officials are contacting those diagnosed with the shigellosis superbug and their contacts with advice about monitoring for symptoms, testing and exclusion requirements.

"Antibiotic-resistant infections are a serious public health problem because infections are harder to treat," the alert read.

Prof Sutton urged people with gastrointestinal symptoms to practice safer sex, maintain good hygiene and avoid preparing food or caring for others.

Victorian clinicians were told to include stool culture when testing patients for shigellosis, only prescribe antibiotics for cases of severe infection, and notify the health department of any shigellosis case within five days of diagnosis.