New Zealand's official swine flu toll rose to 20 on Friday following the death of a woman who battled the virus for more than three months.
The 43-year-old from Waimate had an underlying health condition and spent about 13 weeks in hospitals in Timaru, Christchurch and Auckland. She died on Wednesday night.
The Health Ministry says the woman's family does not want any other details released.
However, deputy director of public health Fran McGrath says there is a pattern of a very severe pneumonia occurring in a small number of people with swine flu.
Dr McGrath says those with existing health conditions such as respiratory illness, pregnancy and obesity are particularly vulnerable to the virus.
She says people with the flu should call their GP if they have underlying health concerns or their condition starts to deteriorate.
Meanwhile, in the United States, health officials say swine flu has killed an estimated 3900 people in the last six months, more than 500 of them children.
The US Center for Disease Control and Prevention says estimates show the flu has infected about 22 million Americans and put 98,000 in hospital.