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Giardiasis is one of the most important non-viral causes of human diarrhoea. Yet, little is known about the epidemiology of giardiasis in the context of developed countries such as Australia and there is a limited information about local sources of exposure to inform prevention strategies in New South Wales. This study aimed to (1) describe the epidemiology of giardiasis and (2) identify potential modifiable risk factors associated with giardiasis that are unique to south-western Sydney, Australia. A 1:2 matched case-control study of 190 confirmed giardiasis cases notified to the South-Western Local Health District Public Health Unit from January to December 2016 was employed to investigate the risk factors for giardiasis. Two groups of controls were selected to increase response rate; Pertussis cases and neighbourhood (NBH) controls. A matched analysis was carried out for both control groups separately. Variables with a significant odds ratio (OR) in the univariate analysis were placed into a multivariable regression for each matched group, respectively. In the regression model with the NBH controls, age and sex were controlled as potential confounders. Identified risk factors included being under 5 years of age (aOR = 7.08; 95% confidence intervals (CI) 1.02–49.36), having a household member diagnosed with a gastrointestinal illness (aOR = 15.89; 95% CI 1.53–164.60) and having contact with farm animals, domestic animals or wildlife (aOR = 3.03; 95% CI 1.08–8.54). Cases that travelled overseas were at increased risk of infection (aOR = 19.89; 95% CI 2.00–197.37) when compared with Pertussis cases. This study provides an update on the epidemiology and associated risk factors of a neglected tropical disease, which can inform enhanced surveillance and prevention strategies in the developed metropolitan areas.

Objective: In developed countries prolonged symptoms due to, or following, Giardia intestinalis infection can have a significant impact on the quality of life. In this research, we investigate the presence of a socioeconomic status (SES) gradient in the reporting of giardiasis in South West Sydney Local Health District (SWSLHD), New South Wales (NSW), Australia, across geographic scales. Methods: We used a large database, spatial-cluster analysis and a linear model. Results: Firstly, we found one spatial cluster of giardiasis in one of the most advantaged neighbourhoods of SWSLHD. Secondly, rates of giardiasis notifications were significantly and consistently lower in SWSLHD compared to an unnamed advantaged Local Health District and NSW over multiple years. Finally, we found an overall significant positive dose-response relationship between counts of giardiasis and area-level SES. Conclusions: Lower reporting in disadvantaged areas may represent true differences in incidence across SES groups or may result from differential use of health services and reporting. Implications for public health: If the disparities result from differential use of health services, research should be directed toward identifying barriers and facilitators of use. If disparities result from a true difference in incidence, then the behavioural mediators between SES and giardiasis should be identified and addressed.

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