Common Infections in Patients Prescribed Systemic Glucocorticoids in Primary Care: A Population-Based Cohort Study

BACKGROUND: Little is known about the relative risk of common bacterial, viral, fungal, and parasitic infections in the general population of individuals exposed to systemic glucocorticoids, or about the impact of glucocorticoid exposure duration and predisposing factors on this risk. METHODS AND FINDINGS: The hazard ratios of various common infections were assessed in 275,072 adults prescribed glucocorticoids orally for ≥15 d (women: 57.8%, median age: 63 [interquartile range 48–73] y) in comparison to those not prescribed glucocorticoids. For each infection, incidence rate ratios were calculated for five durations of exposure (ranging from 15–30 d to >12 mo), and risk factors were assessed. Data were extracted from The Health Improvement Network (THIN) primary care database. When compared to those with the same underlying disease but not exposed to glucocorticoids, the adjusted hazard ratios for infections with significantly higher risk in the glucocorticoid-exposed population ranged from 2.01 (95% CI 1.83–2.19; p < 0.001) for cutaneous cellulitis to 5.84 (95% CI 5.61–6.08; p < 0.001) for lower respiratory tract infection (LRTI). There was no difference in the risk of scabies, dermatophytosis and varicella. The relative increase in risk was stable over the durations of exposure, except for LRTI and local candidiasis, for which it was much higher during the first weeks of exposure. The risks of infection increased with age and were higher in those with diabetes, in those prescribed higher glucocorticoid doses, and in those with lower plasma albumin level. Most associations were also dependent on the underlying disease. A sensitivity analysis conducted on all individuals except those with asthma or chronic obstructive pulmonary disease produced similar results. Another sensitivity analysis assessing the impact of potential unmeasured confounders such as disease severity or concomitant prescription of chemotherapy suggested that it was unlikely that adjusting for these potential confounders would have radically changed the findings. Limitations of our study include the use of electronic medical records, which could have resulted in some degree of misclassification of the infectious outcomes; a possible reporting bias, as general practitioners could be more prone to record an infection in those exposed to glucocorticoids; and a low number of events for some outcomes such as scabies or varicella, which may have led to limited statistical power. CONCLUSIONS: The relative risk of LRTI and local candidiasis is very high during the first weeks of glucocorticoid exposure. Further studies are needed to assess whether low albumin level is a risk factor for infection by itself (e.g., by being associated with a higher free glucocorticoid fraction) or whether it reflects other underlying causes of general debilitation.