Risk of giardiasis in Aucklanders: a case-control study.

BACKGROUND: Giardia is one of the leading protozoal causes of human gastrointestinal illnesses. It is prevalent in both developed and developing countries. Currently, giardiasis is the most commonly notified waterborne disease in New Zealand. The aim of the study was to identify potentially modifiable risk factors for Giardia infection in the adult population in Auckland. METHODS: This case-control study involved 183 Giardia-positive cases and 336 randomly selected controls, aged between 15 and 64 years. Exposure information was collected retrospectively over the telephone for the 21 days preceding the date of onset of symptoms. Both univariate and multiple logistic regression analyses were carried out. RESULTS: The majority of cases were in the 25-44-year age group and in the New Zealand European ethnic group. Housewives and nursing mothers were at significant risk of the disease (odds ratio (OR)=2.06; 95% CI=1.4-3.74), as were the occupational groups exposed to human wastes (OR=4.04, 95% CI=1.85-8.85). Consumption of drinking water from New Zealand supplies other than metropolitan mains supplies (OR=2.11, 95% CI=1.36-3.27) or from sources outside New Zealand (OR=7.97, 95% CI=4.20-15.12) represented a significantly higher risk, as did traveling (OR=7.57, 95% CI=4.03-14.23) and swimming in pools or fresh water at least once a week (OR=2.04, 95% CI= 1.33-3.12). CONCLUSIONS: The study identified potentially modifiable risk factors for Giardia infection. These findings should be investigated further in different groups and settings to ensure better protection of the public health.

Giardia infection in Auckland and New Zealand: trends and international comparison.

AIMS: To describe the epidemiological pattern of Giardia infection in the Auckland region and compare it with national and international patterns of Giardia infection. METHODS: Anonymised giardiasis notification data from the Auckland District Health Board for the period July 1996 to June 2000 were analysed by person, place and time. Infection rates and relative risks were calculated and compared with national and international information. RESULTS: Auckland had a significantly higher rate of Giardia infection than New Zealand as a whole. Infection rates, which peaked during February-May, were significantly higher in Pakeha/Europeans and Asian/others, compared with Maori/Pacificans. Adjusted notification rates were higher for residents of North Shore and Auckland cities than for other areas of Auckland. The crude regional and national notification rates were almost six times the rate of laboratory identification of positive isolates in the UK and four times US reported rates. CONCLUSIONS: The higher rates of giardiasis observed in Auckland and New Zealand, in comparison with other developed countries, may be related to environmental or social factors. Missing ethnicity information precludes clear interpretation of variations in notification rate by ethnic group and suggests a need for improvement in data collection. There are opportunities to investigate the influence of risk factors on seasonal changes in notification rates both locally and nationally.