Using natural strata when examining unmeasured biases in an observational study of neurological side effects of antibiotics.

This article focuses on evaluating the neurological side effects of fluoroquinolone antibiotics in sinusitis patients using a novel observational study design with multiple control groups and a method called natural strata. The study compares 436,891 fluoroquinolone-treated patients to those treated with azithromycin or amoxicillin, employing a new integer programming algorithm to optimally balance many covariates across three treatment groups and two control groups simultaneously. Results indicate a statistically significant association between fluoroquinolones and central or peripheral nervous system complications after the FDA warning, but also reveal strong evidence of unmeasured bias in treatment assignment, as fluoroquinolones are linked to outcomes unlikely to be causally related, such as transfusions and chronic skin ulcers. The authors conclude that while fluoroquinolones may cause neurological side effects, the observed associations could be explained by bias, underscoring the need for cautious interpretation and further research. The study highlights advantages of natural strata in balancing covariates, testing for bias, and maintaining data confidentiality in large observational datasets.