Wedding guests and eight serving staff at the exclusive Northern Club in Auckland fell sick in a suspected norovirus outbreak.
One of the workers was so ill he went to Auckland City Hospital.
His was the only case to have been confirmed as norovirus, said medical officer of health Dr Richard Hoskins.
The wedding was held at the club in Princes St, central Auckland, on Saturday, March 29. People began to fall ill two days later.
Dr Hoskins said the club had alerted the Auckland Regional Public Health Service.
He said the service's investigation was still in progress, and he did not know last night how many of the 100 guests had become ill.
Contact details had been obtained for 77 guests, of whom 44 had been interviewed.
Dr Hoskins understood two pregnant guests were seen at hospital with the illness, although there were no particular risks to pregnancy from norovirus.
"It's not one of those things with high fever that can set off early labour."
Norovirus was usually caused by eating contaminated food or by direct person-to-person contact, he said.
Club's president Tenby Powell said that although the health service's investigation had not yet identified the source of the outbreak, "we are very confident it's got nothing to do with the Northern Club's food handling processes".
The eight affected employees were serving staff - "they serve plates" - and none of the food preparation staff had been affected.
The virus could have been introduced to the premises by anyone who came to the club on the day of the wedding, he said.
The pattern among those who caught the illness - staff and guests - was that people began falling ill on the Monday after the wedding, and the majority became sick on the Tuesday.
"We are very confident none of our staff arrived at work with norovirus that day [the day of the wedding].
"The Northern Club is certified by Auckland Council; it conducts random visits and audits.
"We have, for year after year, been issued with a certificate of compliance. We are sure of our food safety and handling processes.
"The Northern Club has been going since 1869 and, to my knowledge, there hasn't been any outbreak of this sort. It's very distressing for all concerned."
*A virus that can cause vomiting, diarrhoea, headache and fever.
*Incubation period 10-50 hours.
*Symptoms usually last 12 to 72 hours.
*Can be transmitted through contaminated food or water, viral particles spread through the air when a person vomits, or from surfaces such as taps where the virus can survive for some time.
*Treatment - drink extra fluid, and consult a doctor if symptroms are severe.
*Preventing spread - careful clean-up after sick person, and good hand hygiene.