T9-07 Source Attribution for Human Cases of Shiga Toxin-producing Escherichia coli in New Zealand

Wednesday, July 31, 2013: 10:30 AM
213BC (Charlotte Convention Center)
Patricia Jaros, Massey University, Palmerston North, New Zealand
Donald Campbell, Ministry for Primary Industries, Wellington, New Zealand
Adrian Cookson, AgResearch Ltd., Palmerston North, New Zealand
Steve Hathaway, Ministry for Primary Industries, Wellington, New Zealand
Deborah Prattley, Massey University, Palmerston North, New Zealand
Nigel French, Massey University, Palmerston North, New Zealand
Introduction: Shiga toxin-producing Escherichia coli (STEC) O157:H7 and related non-O157 STEC strains are pathogens of public health concern worldwide and can cause life-threatening diseases.  Cattle are considered the principal hosts of STEC and have been shown to be a source of infection for both foodborne and environmental outbreaks in humans overseas.  Since 1993, when New Zealand’s first case of STEC in humans was reported, infections have appeared as sporadic cases and small clusters throughout the country, suggesting highly dispersed animal and/or environmental exposures as the source.  No cases associated with regulated foods have been confirmed.

Purpose: The aim of this study was to investigate risk factors associated with STEC infections in humans in New Zealand and provide epidemiological information on the source and exposure pathways.

Methods: During a national prospective case-control study from July 2011 – July 2012, any confirmed case of STEC infection reported to Public Health Units, together with a random selection of controls representative of the national demography, were interviewed for risk factor evaluation using a standardized questionnaire.  Questionnaire data were analyzed using multivariable logistic regression with multiple imputations to adjust for the small proportion of missing data in some variables.

Results: Data from 113 eligible cases and 506 controls were evaluated.  Animal and environmental risk factors for STEC infections that were statistically significant (P < 0.05) were: cattle livestock being present on meshblock (OR 1.89, 1.04 - 3.42 95% CI) (meshblock is smallest geographical unit statistical data are collected for), having contact with animal manure (OR 2.09, 1.12 - 3.90 95% CI), having contact with recreational waters (OR 2.95, 1.30 - 6.70 95% CI).  However, food-associated risk factors were not identified as sources of STEC infection.

Significance: These findings are somewhat contrary to source attribution information from other countries, strongly indicating that environmental and animal contacts constitute much more important exposure pathways for human cases of STEC in New Zealand than food pathways.