Quasi-experimental study designs, often described as nonrandomized, pre-post intervention studies, are common in the medical informatics literature. Yet little has been written about the benefits and limitations of the quasi-experimental approach as applied to informatics studies. This paper outlines a relative hierarchy and nomenclature of quasi-experimental study designs that is applicable to medical informatics intervention studies. In addition, the authors performed a systematic review of two medical informatics journals, the Journal of the American Medical Informatics Association (JAMIA) and the International Journal of Medical Informatics (IJMI), to determine the number of quasi-experimental studies published and how the studies are classified on the above-mentioned relative hierarchy. They hope that future medical informatics studies will implement higher level quasi-experimental study designs that yield more convincing evidence for causal links between medical informatics interventions and outcomes.

Although a growing number of studies have found a relationship between delayed appropriate antibiotic therapy and mortality, few have attempted to quantify the temporal association between delayed appropriate antibiotic therapy and mortality. This study was designed to measure the elapsed time associated with an increased risk of 30-day mortality among patients with Pseudomonas aeruginosa bacteremia. The retrospective cohort study was conducted among immunocompetent, adult patients with P. aeruginosa bacteremia onset at least 2 days after hospital admission between 1 January 2001 and 30 September 2006. Classification and regression tree analysis (CART) was used to identify the delay in appropriate antibiotic therapy that was associated with an increased risk of 30-day mortality. During the study period, 100 patients met the inclusion criteria. The CART-derived breakpoint between early and delayed treatment was 52 h. The delayed treatment group experienced a >2-fold significant increase in 30-day mortality compared to the early treatment group (44 and 19%, respectively, P ‫؍‬ 0.008). Delayed appropriate therapy of >52 h (odds ratio [OR] ‫؍‬ 4.1; 95% confidence interval [CI] 1.2 to 13.9, P ‫؍‬ 0.03) was independently associated with 30-day mortality in the multivariate analysis. Antibiotic resistance >3 classes (adjusted OR [AOR] ‫؍‬ 4.6; 95% CI ‫؍‬ 1.9 to 11.2, P ‫؍‬ 0.001) and chronic obstructive pulmonary disease (AOR ‫؍‬ 5.4; 95% CI ‫؍‬ 1.5 to 19.7, P ‫؍‬ 0.01) were independently associated with delayed appropriate therapy of >52 h. The data strongly suggest that delaying appropriate therapy for approximately 2 days significantly increases the risk of 30-day mortality in patients with P. aeruginosa bloodstream infections.

Significantly higher rates of gram-negative infection were observed during the summer months, compared with other seasons. For some pathogens, higher temperatures were associated with higher infection rates, independent of seasonality. These findings have important implications for infection prevention, such as enhanced surveillance during the warmer months, and for choice of empirical antimicrobial therapy among hospitalized adults. Future, quasi-experimental investigations of gram-negative infection prevention initiatives should control for seasonal variation.