People who ate at Madam Woo on St Asaph St, Christchurch, on January 15 or 17 may have been exposed to hepatitis A.

Time is running out for diners who may have been exposed to hepatitis A at Christchurch's Madam Woo to get vaccinated.

Health authorities are searching for about 40 walk-in guests who ate at the St Asaph St restaurant on Wednesday January 15, and Friday January 17.

Did you eat food from Madam Woo on either day? Contact newstips@stuff.co.nz

A chef with hepatitis A prepared food at the restaurant on both days, but not January 16.

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Canterbury medical officer of health Dr Ramon Pink said there was a limited timeframe – two weeks – where vaccinations could prevent someone with no previous immunity from developing the disease.

People who dined on January 15 have until Wednesday, January 29 to get vaccinated, and those who dined on January 17 have until this Friday, January 31.

People are considered immune if they have already been vaccinated or have had hepatitis A. Those diners who are not immune are being offered an urgent hepatitis A vaccination.

The local community and public health team had managed to contact most diners through Madam Woo's information, but estimated there were about 40 others.

People who ate food from the restaurant – either dine-in or takeaway (including through a food delivery service) – should call the public health team as soon as possible on 03 364 1777 and ask to speak to a health protection officer.

SUPPLIED People who ate food from the restaurant – either dine-in or takeaway – should call the public health team as soon as possible. (File photo)

In a statement on behalf of Madam Woo, a spokeswoman said the 40 people who had yet to be contacted were walk-in guests so they did not have bookings.

"We are distressed to have been made aware of this potential exposure," she said.

The unwell employee arrived at the restaurant unwell and was sent home on sick leave, the spokeswoman said.

Authorities informed Madam Woo of the health risk on Friday – four days before advice was publicly released.

January 15 and 17 were the employee's rostered days on, she said. "It is important to stress that these are the only possible days of risk, there is no ongoing risk to anyone who dines at Madam Woo."

The restaurant was open as usual on Tuesday.

STUFF Madam Woo was informed of the public health risk by the community and public health team on January 24, four days before advice was publicly released.

WHAT IS HEPATITIS A

Hepatitis A, which is rare in New Zealand, is an infectious disease that stops the liver from working properly. It is transferred through contact with contaminated food and water or close contact with an infected person.

People can be exposed if they eat food prepared by someone with hepatitis A who did not wash their hands after going to the toilet. Symptoms include fever, nausea, abdominal pain, dark urine, pale-coloured faeces and jaundice.

A hepatitis A vaccine is not included as part of the regular vaccine schedule in New Zealand, but is recommended for travel to high risk countries. One dose of the vaccine offers protection for at least a year, while a second booster dose (given six to 12 months after the first dose) gives longer term protection.