Illness and Diseases

Because of limitations in study design and because they represented unexpected findings, we interpreted the results of this outbreak investigation as a paradoxical signal of possible concern—thought‐provoking but inconclusive and warranting further evaluation. Canadian investigators thus embarked on a series of confirmatory studies using more rigorous methods and laboratory‐confirmed outcomes through the summer of 2009, […]

There are, however, several limitations to this study warranting cautious interpretation of the results. First, the study relied upon a nonspecific clinical outcome (ILI) for defining pH1N1‐related illness. There are many causes of ILI, as evidenced by other contributing viruses identified through passive surveillance during the study period. We attempted to validate the ILI case […]

In additional sensitivity analyses based on logistic regression and restricted to the period of peak ILI activity (27 April–11 May 2009), the overall OR for 2008–2009 TIV effect adjusted for age, chronic conditions, Aboriginal status, and household density was higher (3.55; 95% CI, 1.70–7.34). When we used control subjects defined as fully asymptomatic persons rather […]