Geographical variation in the prevalence of asthma symptoms in New Zealand

Aims. To examine geographical variations in the prevalence of asthma symptoms in a random population sample of New Zealand adults aged 20-44 years. Methods. A one page asthma symptom questionnaire was sent to 31 470 people aged 20-44 years. The questionnaire asked about respiratory symptoms, asthma attacks and asthma treatment. Those who had not responded after two reminder postcards were followed with a telephone call where possible. Results. A response rate of 82% (25 664) was achieved. The 12 month period prevalence of asthma (defined as woken by shortness of breath, or an attack of asthma in the past year, or current asthma medication) was 15.2% overall, but was higher in females (17.0%) than in males (13.2%); the prevalence was 22.1% in Maori, 20.6% in Pacific Islanders and 14.3% in non Polynesians. In North Island electorates, the highest age and ethnicity standardised prevalences were found in some of the electorates in the Auckland and Wellington urban regions although prevalence was also high in some rural electorates including Raglan (18.0%), Horowhenua (18.4%) and Wairarapa (18.4%); the lowest prevalences were found in other rural electorates including King Country (5.5%), Matamata (10.1%) and Rotorua (10.3%). In South Island electorates, the highest prevalences were found in some electorates in the Christchurch and Dunedin urban areas, and the lowest prevalences were again found in rural electorates including Clutha (11.3%), Rangiora (9.5%) and Wallace (9.4%). Conclusions. This study confirms the previously reported high frequency of asthma symptoms in New Zealand adults, with higher symptom prevalence in Maori and in women. It shows significant urban/rural differences, as well as marked differences in prevalence between various rural areas. The reasons for these patterns are unclear and require further study.