A prospective case-control and molecular epidemiological study of human cases of Shiga toxin-producing Escherichia coli in New Zealand.

BACKGROUND: Shiga toxin-producing Escherichia coli (STEC) O157:H7 and related non-O157 STEC strains are enteric pathogens of public health concern worldwide, causing life-threatening diseases. Cattle are considered the principal hosts and have been shown to be a source of infection for both foodborne and environmental outbreaks in humans. The aims of this study were to investigate risk factors associated with sporadic STEC infections in humans in New Zealand and to provide epidemiological information about the source and exposure pathways. METHODS: During a national prospective case-control study from July 2011 to July 2012, any confirmed case of STEC infection notified to regional public health units, together with a random selection of controls intended to be representative of the national demography, were interviewed for risk factor evaluation. Isolates from each case were genotyped using pulsed-field gel electrophoresis (PFGE) and Shiga toxin-encoding bacteriophage insertion (SBI) typing. RESULTS: Questionnaire data from 113 eligible cases and 506 controls were analysed using multivariate logistic regression. Statistically significant animal and environmental risk factors for human STEC infections were identified, notably 'Cattle livestock present in meshblock' (the smallest geographical unit) (odds ratio 1.89, 95% CI 1.04-3.42), 'Contact with animal manure' (OR 2.09, 95% CI 1.12-3.90), and 'Contact with recreational waters' (OR 2.95, 95% CI 1.30-6.70). No food-associated risk factors were identified as sources of STEC infection. E. coli O157:H7 caused 100/113 (88.5%) of clinical STEC infections in this study, and 97/100 isolates were available for molecular analysis. PFGE profiles of isolates revealed three distinctive clusters of genotypes, and these were strongly correlated with SBI type. The variable 'Island of residence' (North or South Island of New Zealand) was significantly associated with PFGE genotype (p = 0.012). CONCLUSIONS: Our findings implicate environmental and animal contact, but not food, as significant exposure pathways for sporadic STEC infections in humans in New Zealand. Risk factors associated with beef and dairy cattle suggest that ruminants are the most important sources of STEC infection. Notably, outbreaks of STEC infections are rare in New Zealand and this further suggests that food is not a significant exposure pathway.

Infections with multiple Cryptosporidium species and new genetic variants in young dairy calves on a farm located within a drinking water catchment area in New Zealand.

Several Cryptosporidium species are known to infect cattle. However, the occurrence of mixed infections with more than one species and the impact of this phenomenon on animal and human health are poorly understood. Therefore, to detect the presence of mixed Cryptosporidium infections, 15 immunofluorescence-positive specimens obtained from 6-week-old calves' faeces (n=60) on one dairy farm were subjected to PCR-sequencing at multiple loci. DNA sequences of three Cryptosporidium species: C. parvum (15/15), C. bovis (3/15) and C. andersoni (1/15), and two new genetic variants were identified. There was evidence of mixed infections in five specimens. C. parvum, C. bovis and C. andersoni sequences were detected together in one specimen, C. parvum and C. bovis in two specimens, and C. parvum and C. parvum-like variants in the remaining two specimens. Sequencing of gp60 amplicons identified the IIaA19G4R1 (8/15) and IIaA18G3R1 (4/15) C. parvum subgenotypes. This study provides evidence of endemic mixed infections with the three main Cryptosporidium species of cattle and new genetic variants, in calves at the transition age of six weeks. The results add to the body of evidence describing Cryptosporidium isolates as genetically heterogeneous populations, and highlight the need for iterative genotyping to explore their genetic makeup.