Influence of School Year on Seasonality of Norovirus Outbreaks in Developed Countries.

Factors affecting the seasonal distribution of norovirus outbreaks are not well understood. This study examined whether grade school settings at the start of the school year may be a factor. We searched Ovid Medline from January 2002 to June 2014 for studies that provided all reported norovirus outbreaks in a developed country by month for a minimum of three years. Historical school years were obtained from verifiable sources. The start of the norovirus seasonal outbreak peak and peak outbreak month were determined for each study and compared to the start month of school. Northern hemisphere and southern hemisphere countries had a different norovirus seasonality and different school year structures (traditional compared to year round). In the two studies that provided outbreaks by age, outbreaks among children started several months before outbreaks in the adult population. The median number of months between school start and start of the seasonal outbreak peak was two months (interquartile range [IQR] = 2.0-3.0), while the median number of months between school start and peak outbreak month was four months (IQR = 3.0-4.0). These findings suggest the possibility the school setting at the start of the school year may be a factor in the seasonality of norovirus.

Primary and secondary cases in Escherichia coli O157 outbreaks: a statistical analysis.

BACKGROUND: Within outbreaks of Escherichia coli O157 (E. coli O157), at least 10-15% of cases are thought to have been acquired by secondary transmission. However, there has been little systematic quantification or characterisation of secondary outbreak cases worldwide. The aim of this study was to characterise secondary outbreak cases, estimate the overall proportion of outbreak cases that were the result of secondary transmission and to analyse the relationships between primary and secondary outbreak cases by mode of transmission, country and median age. METHODS: Published data was obtained from 90 confirmed Escherichia coli O157 outbreaks in Great Britain, Ireland, Scandinavia, Canada, the United States and Japan, and the outbreaks were described in terms of modes of primary and secondary transmission, country, case numbers and median case age. Outbreaks were tested for statistically significant differences in the number of ill, confirmed, primary and secondary cases (analysis of variance and Kruskal-Wallis) and in the rate of secondary cases between these variables (Generalised Linear Models). RESULTS: The outbreaks had a median of 13.5 confirmed cases, and mean proportion of 0.195 secondary cases. There were statistically significant differences in the numbers of ill, confirmed, primary and secondary cases between modes of primary transmission (p < 0.021), and in primary and secondary cases between median age categories (p < 0.039) and modes of secondary transmission (p < 0.001).Secondary case rates differed statistically significantly between modes of secondary and primary transmission and median age categories (all p < 0.001), but not between countries (p = 0.23). Statistically significantly higher rates of secondary transmission were found in outbreaks with a median age <6 years and those with secondary transmission via person to person spread in nurseries. No statistically significant interactions were found between country, mode of transmission and age category. CONCLUSION: Our analyses indicated that ~20% of E. coli O157 outbreak cases were the result of secondary spread, and that this spread is significantly influenced by age and modes of primary and secondary transmission, but not country. In particular, the results provide further data emphasising the importance of simple but effective preventive strategies, such as handwashing, that can reduce the risk of secondary spread, particularly amongst young children in nurseries.

Completeness of reporting in abstracts from clinical trials of pre-harvest interventions against foodborne pathogens.

Abstracts are the most commonly read part of a journal article, and play an important role as summaries of the articles, and search and screening tools. However, research on abstracts in human biomedicine has shown that abstracts often do not report key methodological features and results. Little research has been done to examine reporting of such features in abstracts from papers detailing pre-harvest food safety trials. Thus, the objective of this study was to assess the quality of reporting of key factors in abstracts detailing trials of pre-harvest food safety interventions. A systematic search algorithm was used to identify all in vivo trials of pre-harvest interventions against foodborne pathogens in PubMed and CAB Direct published from 1999 to October 2009. References were screened for relevance, and 150 were randomly chosen for inclusion in the study. A checklist based on the CONSORT abstract extension and the REFLECT Statement was used to assess the reporting of methodological features and results. All screening and assessment was performed by two independent reviewers with disagreements resolved by consensus. The systematic search returned 3554 unique citations; 356 were found to be relevant and 150 were randomly selected for inclusion. The abstracts were from 51 different journals, and 13 out of 150 were structured. Of the 124 abstracts that reported whether the trial design was deliberate disease challenge or natural exposure, 113 were deliberate challenge and 11 natural exposure. 103 abstracts detailed studies involving poultry, 20 cattle and 15 swine. Most abstracts reported the production stage of the animals (135/150), a hypothesis or objective (123/150), and results for all treatment groups (136/150). However, few abstracts reported on how animals were grouped in housing (25/150), the location of the study (5/150), the primary outcome (2/126), level of treatment allocation (15/150), sample size (63/150) or whether study units were lost to follow up (4/150). Forty-eight (48/150) abstracts reported the name, mode of administration, dose and duration of the intervention(s), while 102 (102/150) reported at least one of these elements. Nine (9/150) abstracts specified that allocation of study units to treatments was randomized, and none of the abstracts reported whether blinding was used (0/150). These results reveal gaps in reporting of methodological features and results. Thus, improving reporting quality in abstracts should be a crucial goal to be pursued by authors, reviewers and journal editors.

Analysis of trends in the full publication of papers from conference abstracts involving pre-harvest or abattoir-level interventions against foodborne pathogens.

Study results are often presented as abstracts at scientific conferences before publication as full articles in peer-reviewed journals. Given the current emphasis on evidence-based decision-making, it is vital that the peer-reviewed literature represents as broad and un-biased a selection of studies as possible. While the proportion of abstracts published as full papers in the peer-reviewed literature has been extensively studied in human healthcare, no such studies have been published in the field of food safety. The goal of this study was to estimate the proportion published and average time to publication for conference abstracts involving studies of pre-harvest or abattoir interventions to reduce foodborne pathogens. Abstracts were obtained by hand-searching available proceedings between 1995 and 2004 from 10 conferences. Included abstracts were limited to those detailing non-observational, controlled in vivo trials where outcome(s) were measured in livestock, carcasses or eggs. Data on abstract type (500 words), species, intervention, study type, sample size, number housed together and outcomes were recorded. Four databases (Agricola, CAB, Web of Science, Scholar's Portal) were searched for published papers corresponding to the conference abstracts using author and intervention/pathogen terms. Time to publication and overall median time to publication were estimated. Chi-squared, logistic regression and survival analyses were used to test for significant differences in proportion published and time to publication between variable levels. Of the 149 abstracts identified, 68 (45.6%) were published in peer-reviewed journals within 4 years. The median time to publication was 13.5 months (range: 0, 72). Abstracts shorter than 1 page were significantly more likely to be published (OR=2.2, 95% CI=1.0, 4.8), and abstracts involving pork or pigs were significantly less likely to be published that those involving poultry (OR=0.4: 0.2, 0.8). Abstracts reporting at least one positive outcome were more likely to be published (OR=2.608: 1.097, 6.196) and were published faster (HR=2.3: 1.1, 4.7). Time to publication decreased with the number of positive outcomes reported (HR=1.1: 1.0, 1.3). Sample size could only be determined for 46% of abstracts, with a median sample size of 9 (range 1-378), and housing was sufficiently described to determine sample size in 35% of pre-slaughter studies. The potential effects of this bias on systematic reviews and uses of interventions could be significant, and thus improvements may be warranted in the proportion of conference abstracts resulting in papers in the peer-reviewed literature.

Comparison of outcomes and other variables between conference abstracts and subsequent peer-reviewed papers involving pre-harvest or abattoir-level interventions against foodborne pathogens.

Accuracy in the reporting of studies in conference abstracts is important because the majority of studies in such abstracts are never further detailed in peer-reviewed publications, and data from such abstracts may be used in systematic reviews. Previous research on interventional studies in human biomedicine indicates that there is no guarantee of consistency between a conference abstract and paper in the reporting of results and other key variables. However, no research has been done to determine if this lack of reporting consistency in abstracts and papers extends to interventional studies in pre-harvest/harvest-level food safety. The goal of this study was to compare outcome results and other key variables between conference abstracts and subsequent peer-reviewed publications describing studies of pre-harvest and abattoir-level interventions against foodborne pathogens, and to determine whether the agreement in the results or key variables was associated with the time to full publication. A systematic search identified 59 conference abstracts with matching peer-reviewed papers (matches), and data on variables including outcome measures and results, pathogens, species, interventions, overall efficacy of intervention, sample size and housing were extracted from both the conference abstracts and the papers. The matching of variables between abstracts and papers was described, and logistic regression used to test for associations between variable matching and time to publication. Sample size was only provided for both abstract and paper in 24 matches; the same sample size was reported in 20 of these matches. Most other variables were reported in the majority of abstracts/papers, and with the exception of outcomes and intervention effect, the reporting of variables was relatively consistent. There was no significant difference in the numbers of authors, with the first author the same in 78.3% of matches. Of 231 outcome measures reported in both abstracts and papers, nearly one third (77% or 32.2%) had different results, with 32 changing direction of effect. More than a quarter of matches involved at least one significant change in outcome result. The overall conclusion on the efficacy of the intervention changed in 10.7% of matches. There was a significant association between increased time to publication and differences in the number of authors, and having fewer outcome measures in the abstract reported in the paper. These results suggest that data from conference abstracts should be considered with caution.