The Ministry of Health says it is yet to find the source of a salmonella gastroenteritis outbreak.
There have been 36 reported cases of the stomach bug from Auckland to Dunedin since 13 October, including 16 in Christchurch.
Others were in Dunedin (9), Nelson (5), Greymouth (1), Rotorua (1), Whakatane (1), Waikato (1) and Auckland (2).
The ministry's chief adviser of population health, Greg Simmons, says five people have been hospitalised with the bug, which causes fever, headache, abdominal pain, diarrhea and vomiting.
Very young people, the elderly and the immune compromised may become severely dehydrated if they become ill.
Dr Simmons says ESR and the Food Safety Authority are trying to find the source of the infection.
There were a total of 15 cases in 2007 and 28 cases in 2006.