Association between oral contraceptives and serious infections: A population-based cohort study

Aims: Oral contraceptives (OC)s are commonly used worldwide. In a recent study, we showed that the use of OCs is associated with an increased risk for neutropenia. We aimed to investigate the clinical implications of this finding by examining the infection rates of 4 serious infections before, during and after OCs.

Methods: A retrospective cohort study using the electronic medical records of a large health organization. We selected 2 retrospective cohorts of women aged 16-40 between years 2005 and 2019. The first cohort examined infection rates during 2 years before OC use and 2 consecutive years of adherent OC use. The second cohort included women who consumed OCs adherently for 2 years and then discontinued their use for 2 consecutive years. Women's infection rates were compared by χ² test, results were stratified by OC type and age.

Results: Overall, 21 595 and 20 728 women were included in Cohorts 1 and 2 respectively. We found a statistically significant higher relative risk for infection while using OCs; the overall risk ratios (95% confidence intervals) for infection in Cohorts 1 and 2 were 1.35 (1.32-1.38) and 1.27 (1.24-1.31), respectively. The overall infection risk remained statistically significant when stratified by age.

Conclusions: This study demonstrates a high statistically and clinically significant risk for all infections followed during OC consumption, which is likely to have major clinical and economic implications. These findings may have implications to millions of women worldwide and should lead to more research on the safety of the pill.