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Lærke Storgaard Duerlund,1 Shakil Shakar,2 Henrik Nielsen,1 Jacob Bodilsen1 1Department of Infectious Diseases, Aalborg University Hospital, Aalborg, Denmark; 2The Department of Medicine, Regionshospitalet Nordjylland Hjørring, Hjørring, DenmarkCorrespondence: Jacob BodilsenDepartment of Infectious Diseases, Aalborg University Hospital, Mølleparkvej, 4, Aalborg, 9000, Denmark, Tel +45 97660566, Email Jacob.bodilsen@rn.dkPurpose: To examine the positive predictive value (PPV) of International Classification version 10 (ICD-10) diagnosis codes for long coronavirus disease 2019 (long-COVID) in a Danish Health registry.Patients and Methods: This was a medical record review of all patients with a diagnosis code of long-COVID (DB948A) at all hospitals in the North Denmark Region from February 27, 2020 through June 30, 2021. Confirmed long-COVID was categorized as fulfillment of all three criteria: (1) a positive polymerase chain reaction (PCR) test for SARS-CoV-2 on a respiratory sample or a positive serum antibody test, (2) symptoms suggestive of long-COVID with no other diagnosis considered more likely, and (3) symptom duration > 6 weeks.Results: A total of 306 patients were assigned a hospital diagnosis code for long-COVID corresponding to 1.4% of all SARS-CoV-2 positive individuals during the study period (n=21,727). Next, 40 patients were excluded due to incomplete diagnostic evaluation at time of record review leaving 266 patients for analysis. The patients had a median age of 51 years (interquartile range 43– 60) and 175/266 (66%) were females. Long-COVID was confirmed in 249/266 yielding an overall PPV of 94% (95%CI: 90– 96) and did not differ substantially according to most age groups, sex, previous hospitalization for COVID-19, or by using 12 weeks of symptom duration as cut-off. The PPV was low for children and adolescents (n=5), the very elderly (n=9), and those included by secondary long-COVID diagnoses (n=10).Conclusion: The overall PPV of diagnosis codes for long-COVID in the North Denmark Region was high and was likely suitable for future registry-based studies of long-COVID. Caution is advised at the extremes of age and secondary diagnosis codes.Keywords: post-COVID, coronavirus disease 2019, diagnosis codes, validation, epidemiology

Jacob Bodilsen,1 Lykke Larsen,2 Christian Thomas Brandt,3,4 Lothar Wiese,4 Birgitte Rønde Hansen,5 Christian Østergaard Andersen,6 Hans Rudolf Lüttichau,7 Jannik Helweg-Larsen,8 Merete Storgaard,9 Henrik Nielsen1,10 1Department of Infectious Diseases, Aalborg University Hospital, Aalborg, 9000, Denmark; 2Department of Infectious Diseases, Odense University Hospital, Odense, 5000, Denmark; 3Department of Infectious Diseases, Nordsjællands Hospital, Hillerød, 3400, Denmark; 4Department of Infectious Diseases, Sjælland University Hospital, Roskilde, 4000, Denmark; 5Department of Infectious Diseases, Hvidovre University Hospital, Copenhagen, 2650, Denmark; 6Department of Clinical Microbiology, Hvidovre University Hospital, Copenhagen, 2650, Denmark; 7Department of Infectious Diseases, Herlev Gentofte Hospital, Copenhagen, 2730, Denmark; 8Department of Infectious Diseases, Rigshospitalet, Copenhagen, 2100, Denmark; 9Department of Infectious Diseases, Aarhus University Hospital, Aarhus, 8200, Denmark; 10Department of Clinical Medicine, Aalborg University, Aalborg, 9000, DenmarkCorrespondence: Jacob BodilsenDepartment of Infectious Diseases, Aalborg University Hospital, Mølleparkvej 4, Aalborg, DK9000, DenmarkTel +45 97660566Email Jacob.bodilsen@rn.dkAbstract: Central nervous system (CNS) infections are rare diseases that are associated with considerable morbidity and mortality. Increased knowledge based on contemporary data is a prerequisite for improved management and prevention of these serious conditions. Yet, population-based databases of patients hospitalized with CNS infections remain scarce. The Danish Study Group of Infections of the Brain (DASGIB) has prospectively registered information on all adults ≥ 18 years of age admitted with CNS infections at departments of infectious diseases in Denmark since 2015. The main variables collected are baseline demographics, blood and cerebrospinal fluid tests, imaging results, and outcome using the Glasgow Outcome Scale score. To investigate important aspects for each type of CNS infections, additional variables are included specifically for bacterial meningitis, viral meningitis, encephalitis, brain abscess, neurosyphilis, and Lyme neuroborreliosis. From 2015 to 2020, a total of 3579 cases of CNS infections have been recorded in the DASGIB database. Using the unique civil registration number assigned to all Danish residents, the database can be unambiguously linked with nationwide healthcare registries at the individual level. This enables researchers to conduct detailed population-based and longitudinal observational studies of risk and prognosis of CNS infections and to compare them with matched population cohorts. The database is well-suited for epidemiological research and the DASGIB network forms a solid infrastructure for future national and international collaborations.Keywords: CNS infections, epidemiology, database, cohort studies, bacterial meningitis, viral meningitis, encephalitis, brain abscess, cerebral abscess, neurosyphilis, syphilis, Lyme neuroborreliosis, borreliosis

Jacob Bodilsen,1 Michael Dalager-Pedersen,1 Nicolai Kjærgaard,1 Diederik van de Beek,2 Matthijs C Brouwer,2 Henrik Nielsen,1 and the DASGIB study group 1Department of Infectious Diseases, Aalborg University Hospital, Aalborg, Denmark; 2Department of Neurology, Amsterdam Neuroscience, Academic Medical Centre, Amsterdam, The Netherlands Purpose: To evaluate the positive predictive value (PPV) of ICD-10 diagnosis codes for brain abscess in the Danish National Patient Registry (DNPR). Patients and methods: We examined medical records of all patients with a first-time diagnosis code of brain abscess in the DNPR from 2007 to 2016. Patients were categorized with either confirmed or disproved brain abscess using a priori defined criteria. We computed the PPV as the proportion of confirmed diagnoses. Results: We identified 709 patients, of whom the medical records could not be retrieved for 15 patients, leaving 694 for further analyses. Of these, 444 had a confirmed brain abscess and 250 had another proven diagnosis, including 47 cases of intracranial empyema. The overall PPV was 64% (95% CI: 60–68) ranging from 24% to 96% among the different codes evaluated. By including only patients with either 1) both a diagnosis and surgical procedure code for brain abscess or 2) patients admitted to hospital with certain primary diagnosis codes (DG060[C,E,F] or DG079B) without newly diagnosed central nervous system (CNS) cancer, spondylodiscitis/intraspinal abscess, or procedure codes for evacuation of intracranial empyema, the PPV increased to 84% (95% CI 80–87) and 89% (395/444) of all confirmed cases were identified. Conclusion: The overall PPV of diagnosis codes for brain abscess in the DNPR was moderate. However, by exclusion of newly diagnosed CNS tumors, spondylodiscitis/intraspinal abscess, and intracranial empyemas, the PPV was high and therefore suitable for future registry-based studies of brain abscess. Keywords: cerebral abscess, register, PPV, intracranial abscess, epidemiology

To examine the incidence and mortality of brain abscesses. We accessed nationwide population-based medical registries to obtain data for patients with first-time brain abscesses in Denmark from 1982 through 2016. Annual age- and sex-standardized incidence rates with 95% confidence intervals were calculated and compared by direct standardization. We used Cox regression to compute mortality rate ratios adjusted for age and year groups, sex and Charlson comorbidity index score. We identified 1384 patients (37% female). The overall standardized incidence rate of brain abscess was 0.76 per 100 000 person-years (95% confidence interval 0.70–0.81). The incidence rates gradually increased from 0.60 during 1982–88 to 0.90 per 100 000 person-years during 2010–16, yielding an incidence rate ratio of 1.50 (95% confidence interval 1.26–1.79). This increase in incidence was most pronounced in the proportions of brain abscess patients >40 years of age and those with immuno-compromise. The 1-year mortality declined from 29% during 1982–88 to 20% during 2010–16, yielding an adjusted mortality rate ratio of 0.44 (95% confidence interval 0.31–0.63). Risk factors for death were advanced age, Charlson comorbidity index >0, immuno-compromised status and congenital heart disease. The incidence of brain abscess in Denmark is low but increasing, especially in the elderly, along with an increasing proportion of brain abscess patients with immuno-compromise. The prognosis has improved during the last decades, but mortality remains high. Risk factors for death in our study were advanced age, presence of comorbidity, immuno-compromised status and congenital heart disease. [ABSTRACT FROM AUTHOR]

Abstract Objectives To monitor epidemiological trends of infectious meningitis (bacterial and viral) and encephalitis in Denmark. Methods Nationwide prospective observational study of all cases of proven community-acquired infectious meningitis and encephalitis in adults treated in all infectious diseases departments in Denmark from 1 January 2015 to 30 June 2016. We included data on symptoms, aetiology, treatment and outcome assessed by the Glasgow Outcome Scale (GOS) 30 days after discharge. GOS 1–4 was categorized as unfavourable outcome. Results During 18 months of observation, we identified 252 cases of viral meningitis (3.6/100 000/year), 214 cases of bacterial meningitis (3.1/100 000/year) and 96 cases of infectious encephalitis (1.4/100 000/year). In bacterial meningitis, Streptococcus pneumoniae was the most frequent infectious agent (n = 101) followed by Staphylococcus aureus (n = 24) and β-haemolytic streptococci (n = 14). Meningococcal meningitis was rare (n = 11). In encephalitis, herpes simplex virus type 1 was most common (n = 37) followed by varicella zoster virus (n = 20), whereas varicella zoster virus (n = 61) was most common in viral meningitis followed by enterovirus (n = 50) and herpes simplex virus type 2 (n = 46). Case fatality and unfavourable outcome occurred in 31/214 (15%) and 96/214 (45%) with bacterial meningitis and in 5/96 (5%) and 55/89 (62%) with encephalitis. For viral meningitis, unfavourable outcome occurred in 41/252 (17%). Conclusions The epidemiology and clinical presentation of the examined central nervous system infections differed considerably and bacterial meningitis was more frequent than previously estimated. Overall prognosis remains poor for bacterial meningitis and encephalitis. Prospective nationwide clinical databases of central nervous system infections may be superior to epidemiological monitoring based on notifications or laboratory systems. [ABSTRACT FROM AUTHOR]