Papers by Caitlin Johnson
PloS one, 2011
Background We designed a seroprevalence study using multiple testing assays and population source... more Background We designed a seroprevalence study using multiple testing assays and population sources to estimate the community seroprevalence of pH1N1/09 and risk factors for infection before the outbreak was recognized and throughout the pandemic to the end ...
Clinical Infectious Diseases
Background Vaccine effectiveness (VE) studies provide essential evidence on waning vaccine-derive... more Background Vaccine effectiveness (VE) studies provide essential evidence on waning vaccine-derived immunity, a major threat to pertussis control. We evaluated how study design affects estimates by comparing two case-control studies conducted in Ontario, Canada. Methods We compared results from a test-negative design (TND) with a frequency-matched design (FMD) case-control study using pertussis cases from 2005-15. In the first study, we identified test-negative controls from the public health laboratory that diagnosed cases and in the second, randomly selected controls from patients attending the same physicians that reported cases, frequency-matched on age and year. We compared characteristics of cases and controls using standardized differences. Results In both designs, VE estimates for the early years post-immunization were consistent with clinical trials (TND 84%, FMD 89% at 1-3 years post-vaccination), but diverged as time since last vaccination increased (TND 41% and FMD 74% by...
The Journal of Special Education, 2011
This study examined the influences of problem behaviors on kindergarten reading outcomes and inve... more This study examined the influences of problem behaviors on kindergarten reading outcomes and investigated the extent to which explicit, code-based reading instruction moderated those relations among 206 children identified as being at risk of reading difficulty. Children from the classrooms of 57 kindergarten teachers in 12 schools were randomly assigned to an early reading intervention program or school-determined comparison intervention. In both conditions, children received 30 minutes of small-group supplementary reading instruction for 21 weeks. Findings from multilevel modeling revealed many associations between problem behaviors and reading outcomes for children in both conditions. Interaction analyses indicated that explicit, code-based reading intervention moderated the negative impact of externalizing problem behavior on end-of-kindergarten measures of alphabet knowledge, phonemic blending, and word reading. This type of intensive systematic reading instruction also moderat...
Journal of Cardiac Failure, 2013
Earlier work has demonstrated significant sex and age disparities in ischemic heart disease. Howe... more Earlier work has demonstrated significant sex and age disparities in ischemic heart disease. However, it remains unclear if an age or sex gap exists for heart failure (HF) patients. Using data from the 2007-2008 Healthcare Cost and Utilization Project, we constructed hierarchic regression models to examine sex differences and age-sex interactions in HF hospitalizations and in-hospital mortality. Among 430,665 HF discharges, 51% were women and 0.3%, 27%, and 73% were aged <25, 25-64, and >64 years respectively. There were significant sex differences among HF risk factors, with a higher prevalence of coronary disease among men. Men had higher hospitalization rates for HF and in-hospital mortality across virtually all ages. The relationship between age and HF mortality appeared U-shaped; mortality rates for ages <25, 25-64, and…
BMC Public Health, 2012
Background: Increases in the number of salmonellosis cases due to Salmonella Enteritidis (SE) in ... more Background: Increases in the number of salmonellosis cases due to Salmonella Enteritidis (SE) in 2010 and 2011 prompted a public health investigation in Ontario, Canada. In this report, we describe the current epidemiology of travel-related (TR) SE, compare demographics, symptoms and phage types (PTs) of TR and domestically-acquired (DA) cases, and estimate the odds of acquiring SE by region of the world visited. Methods: All incident cases of culture confirmed SE in Ontario obtained from isolates and specimens submitted to public health laboratories were included in this study. Demographic and illness characteristics of TR and DA cases were compared. A national travel survey was used to provide estimates for the number of travellers to various destinations to approximate rates of SE in travellers. Multivariate logistic regression was used to estimate the odds of acquiring SE when travelling to various world regions. Results: Overall, 51.9% of SE cases were TR during the study period. This ranged from 35.7% TR cases in the summer travel period to 65.1% TR cases in the winter travel period. Compared to DA cases, TR cases were older and were less likely to seek hospital care. For Ontario travellers, the adjusted odds of acquiring SE was the highest for the Caribbean (OR 37.29, 95% CI 17.87-77.82) when compared to Europe. Certain PTs were more commonly associated with travel (e.g., 1, 4, 5b, 7a, Atypical) than with domestic infection. Of the TR cases, 88.9% were associated with travel to the Caribbean and Mexico region, of whom 90.1% reported staying on a resort. Within this region, there were distinct associations between PTs and countries. Conclusions: There is a large burden of TR illness from SE in Ontario. Accurate classification of cases by travel history is important to better understand the source of infections. The findings emphasize the need to make travellers, especially to the Caribbean, and health professionals who provide advice to travellers, aware of this risk. The findings may be generalized to other jurisdictions with travel behaviours in their residents similar to Ontario residents.
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Papers by Caitlin Johnson