Hospitalisations with infectious disease diagnoses in somatic healthcare between 1998 and 2019: A nationwide, register-based study in Swedish adults.

Background: Several studies indicate increasing hospitalisation rates for specific infectious diseases (IDs). Studies describing the entire ID spectrum are scarcer. Our aim was to describe hospital use with ID diagnoses in Swedish adults from 1998 to 2019. Methods: All four-position codes in ICD-10 were reclassified as ID or non-ID diagnoses. Using data from the National Patient Register, age-standardised hospitalisation rates and average length-of-stay (LOS) was determined for hospitalisations with ID vs non-ID diagnoses in the primary position at discharge. The 22-year study period was divided into five periods that were compared using standardised rate ratios (SRR). Findings: Annual hospitalisations with ID diagnoses increased from 115 thousand in 1998-2002 to 182 thousand in 2015-2019, for a rate increase from 17·4 to 23.0 per 1000 person-years, and a SRR (95%CI) of 1.32 (1.32-1.33). Concurrently, the hospitalisation rate with non-ID diagnoses decreased from 147 to 110, for a SRR of 0.75 (0.75-0.75). Average LOS decreased less for IDs than for non-IDs. Consequently, the proportion of hospital nights for which an ID was considered causing the hospitalisation increased from 11% to 21%. Persons aged 80+ years had the highest ID hospitalisation rate. Interpretation: The increased hospital use with ID diagnoses suggests an increasing incidence of severe IDs as well as a changing case-mix of hospitalised patients. Given the anticipated demographic change, this trend is likely to persist. Healthcare systems will need to address IDs in a comprehensive and standardised way. Funding: Governmental Funding of Research within the Clinical Sciences (ALF).