Discussion
In this study, which is based on surveillance data from Beredt C19, we have shown that 0.69 % of residents in Norwegian nursing homes were infected in the first year of the pandemic during their stay in a nursing home, and that 1.3 % of all deaths among nursing home residents were related to COVID-19.
High age has previously been shown to be the strongest predictor of death after contracting COVID-19 (5). Norwegian nursing home residents have a high rate of multimorbidity and require a high level of care (6). However, we also find that high age increases the risk of death in this population. The fact that most of the deaths were observed before or during the peak infection levels may indicate that infection rates were higher than reflected in the testing. This further indicates that the external infection rate is the main factor behind the number of deaths in nursing homes, which is consistent with previous research (7). This is also corroborated by the observation that the incidence rate for SARS-CoV-2 infections appears to follow the incidence rate in society as a whole.
In 2020, approximately one-half of all COVID-19-related deaths in Norway occurred in nursing homes (8). This must be seen in light of the nursing home population's high background mortality and the fact that approximately one-half of all deaths normally occur in nursing homes (9). Guidelines from the Norwegian Directorate of Health stipulated that nursing home residents with COVID-19 should not be transferred to hospitals (10). Accordingly, we found that few residents were transferred to hospitals. However, many temporary residents had recently been discharged from hospital, which may indicate that the nursing homes constitute a key link in the patient chain for COVID-19 and thus for health preparedness, since patients may need a prolonged stay at a different treatment level after the acute phase. In other words, full nursing homes may impede hospital discharges.
The strength of our analyses lies in the quality and scope of the Beredt C19 emergency preparedness register. There are some weaknesses, however. The data set 'Health and Care' in the Norwegian Registry for Primary Health Care has not previously been used in this manner, and no validation studies are therefore available to indicate whether our register definition is correct or not. A register definition will rarely cover the general definition of a concept precisely. By including all units engaged in health-oriented business activities or municipal administration, in addition to temporary stays, we are likely to have included more persons than what many would consider to be 'nursing home residents'. Moreover, many residents who were granted temporary residence actually stayed in the nursing home for the entire year, as the original stay was extended. Therefore, it is not necessarily the case that long-term residents have poorer health than temporary residents. Long-term residents also have a longer follow-up time in the cohort and thus a higher cumulative risk of experiencing one of the outcomes. In addition, the interpretation needs to take into account that testing regimes did not detect all infections. Nor have we had access to clinical data for the residents.
Norwegian nursing home residents have borne a large proportion of the mortality burden from COVID-19 during the pandemic, but due to the high background mortality, COVID-19-related deaths accounted for a relatively minor proportion of these. In this brief report, we have shown how the 'Health and Care' data set in the Norwegian Registry for Primary Health Care can be combined with other data sources to monitor the Norwegian nursing home population. The nursing home population constitutes a group that also has a high disease burden under normal circumstances, but in spite of this fact, little surveillance and research are undertaken in relation to this group. Future register-based research on nursing home residents should be based on and further develop this register definition.