This analysis is the first comparison of different data sources that collect data on hospitalisations for COVID-19 in Norway, and as far as we are aware the first to compare results from three different data sources. Few similar analyses from other countries have been published. In an analysis of two different data sources on hospitalisations for COVID-19 in Belgium, 71 per cent of hospitalisations were registered in a system that was based on voluntary reporting of individual-level data, compared with a mandatory reporting system based on collection of aggregated data (2). In our study, there were nearly one hundred more new admissions for COVID-19 in NPR-MSIS than in NIPaR at the start of the study period, and more hospitalised patients per day in March. This could be due to some patients admitted to hospital before the pandemic registry came into operation not being registered retrospectively, or patients without a national identity number or a D-number (a temporary identity number for foreign residents) not being able to be registered. Since November 2020 it has been possible to link NIPaR to MSIS in the Beredt C19 registry, which enables further analysis of differences between these two data sources in terms of patients registered.
The trend in the number of hospitalised patients per day in the three sources confirms that the figures reported to the Directorate of Health have given a good picture of the situation in Norway during the COVID-19 pandemic. Day-to-day variation between the data sources in the number of hospitalised patients can be due to differences in data collection practices and in the ways in which patient trajectories are collated. The reporting to the Directorate of Health was crucial at the start of the COVID-19 pandemic when the other two data sources were unavailable, and it also reveals a gap in preparedness that also came to light in connection with the influenza pandemic in 2009, both in Norway (7, 11) and internationally (12, 13). The reporting to the Directorate of Health required a manual daily count, at a time when the health authorities were facing a substantial workload. The concurrent results give grounds for assessing whether NIPaR and NPR-MSIS can replace the hospitals' reporting to the Directorate of Health. It is desirable to have automated systems in place that use existing data instead of manual solutions, but both of these approaches are required for the time being.
The daily data retrievals from the hospitals' electronic systems (NPR) that have been established during the pandemic are a major step in the direction of updated registry information from the Norwegian specialist health service. A continuation of this practice also after the pandemic will be important to improve the national monitoring of future known and unknown serious health threats. NPR-MSIS provides a quick and complete registration of admissions and discharges of patients infected by SARS-CoV-2, because the linkage is largely based on established reporting procedures. On the other hand, it is difficult to determine whether the patient is being treated for COVID-19 or for some other disease or injury. Registration in NIPaR requires is done manually, and thereby has similar disadvantages to those of registration by the Directorate of Health. The advantage is that NIPaR collects far more clinical information, which makes this source well suited for analysing the condition of COVID-19 patients and the therapeutic procedures that are initiated.
As national registries, NIPaR and NPR-MSIS can be used for ongoing research and surveillance of COVID-19. If the information in NIPaR and NPR-MSIS is also to be used in the context of emergency preparedness, it is essential that these data sources provide updated, real-time information on the workload in hospitals that can quickly be fed back to decision-makers. In an emergency preparedness situation, information gathering needs to be robust and feasible without burdening the health services, especially the clinicians. Information ought to be collected from persons without a national ID number or D-number as well as from any recently established hospitals and intensive care units.
This study is retrospective, and the information from NIPaR and NPR-MSIS has been adjusted retrospectively. This may explain why more hospitalised patients were generally registered in NIPaR and NPR-MSIS than in the figures from the Directorate of Health. The results are therefore not transferable to an emergency preparedness situation where daily updated information is required. An analysis based on a daily data retrieval from NIPaR and NPR-MSIS must be undertaken over a period to be able to assess whether these data sources are suitable as replacements for the hospitals' reporting to the Directorate of Health.
The number of patients on ventilatory support was higher in NPR-MSIS than in NIPaR, and the number of patients on invasive ventilatory support was higher in NPR-MSIS than in the figures from the Directorate of Health. In NPR-MSIS, the end time of ventilatory support was based on the time of discharge from the ward, due to incomplete or missing data for end time of ventilatory support. Most likely, this has led to an overestimation of the number of patients on ventilatory support at any given time. NIPaR is therefore better suited to measure the time on ventilatory support. Another possibility is to increase the quality of the coding of start and end times for implemented interventions and procedures in NPR.