The epidemiology of multidrug-resistant organisms in persons diagnosed with cancer in Norway, 2008-2018: expanding surveillance using existing laboratory and register data.

Surveillance has revealed an increase of multidrug-resistant organisms (MDROs), even in low-prevalent settings such as Norway. MDROs pose a particular threat to at-risk populations, including persons with cancer. It is necessary to include such populations in future infection surveillance. By combining existing data sources, we aimed to describe the epidemiology of MDROs in persons diagnosed with cancer in Norway from 2008 to 2018. A cohort was established using data from the Cancer Registry of Norway, which was then linked to notifications of methicillin-resistant Staphylococcus aureus (MRSA), vancomycin- and/or linezolid-resistant enterococci (V/LRE), and carbapenemase-producing Gram-negative bacilli (CP-GNB) from the Norwegian Surveillance System for Communicable Diseases, and laboratory data on third-generation cephalosporin-resistant Enterobacterales (3GCR-E) from Oslo University Hospital (OUH). We described the incidence of MDROs and resistance proportion in Enterobacterales from 6 months prior to the person's first cancer diagnosis and up to 3 years after. The cohort included 322,005 persons, of which 0.3% (878) were diagnosed with notifiable MDROs. Peak incidence rates per 100,000 person-years were 60.9 for MRSA, 97.2 for V/LRE, and 6.8 for CP-GNB. The proportion of 3GCR-E in Enterobacterales in blood or urine cultures at OUH was 6% (746/12,534). Despite overall low MDRO incidence, there was an unfavourable trend in the incidence and resistance proportion of Gram-negative bacteria. To address this, there is a need for effective infection control and surveillance. Our study demonstrated the feasibility of expanding the surveillance of MDROs and at-risk populations through the linkage of existing laboratory and register data.

The population structure of vancomycin-resistant and -susceptible Enterococcus faecium in a low-prevalence antimicrobial resistance setting is highly influenced by circulating global hospital-associated clones.

Between 2010 and 2015 the incidence of vancomycin-resistant Enterococcus faecium (VREfm) in Norway increased dramatically. Hence, we selected (1) a random subset of vancomycin-resistant enterococci (VRE) from the Norwegian Surveillance System for Communicable Diseases (2010-15; n=239) and (2) Norwegian vancomycin-susceptible E. faecium (VSEfm) bacteraemia isolates from the national surveillance system for antimicrobial resistance in microbes (2008 and 2014; n=261) for further analysis. Whole-genome sequences were collected for population structure, van gene cluster, mobile genetic element and virulome analysis, as well as antimicrobial susceptibility testing. Comparative genomic and phylogeographical analyses were performed with complete genomes of global E. faecium strains from the National Center for Biotechnology Information (NCBI) (1946-2022; n=272). All Norwegian VREfm and most of the VSEfm clustered with global hospital-associated sequence types (STs) in the phylogenetic subclade A1. The vanB2 subtype carried by chromosomal Tn1549 integrative conjugative elements was the dominant van type. The major Norwegian VREfm cluster types (CTs) were in accordance with concurrent European CTs. The dominant vanB-type VREfm CTs, ST192-CT3/26 and ST117-CT24, were mostly linked to a single hospital in Norway where the clones spread after independent chromosomal acquisition of Tn1549. The less prevalent vanA VRE were associated with more diverse CTs and vanA carrying Inc18 or RepA_N plasmids with toxin-antitoxin systems. Only 5 % of the Norwegian VRE were Enterococcus faecalis, all of which contained vanB. The Norwegian VREfm and VSEfm isolates harboured CT-specific virulence factor (VF) profiles supporting biofilm formation and colonization. The dominant VREfm CTs in general hosted more virulence determinants than VSEfm. The phylogenetic clade B VSEfm isolates (n=21), recently classified as Enterococcus lactis, harboured fewer VFs than E. faecium in general, and particularly subclade A1 isolates. In conclusion, the population structure of Norwegian E. faecium isolates mirrors the globally prevalent clones and particularly concurrent European VREfm/VSEfm CTs. Novel chromosomal acquisition of vanB2 on Tn1549 from the gut microbiota, however, formed a single major hospital VREfm outbreak. Dominant VREfm CTs contained more VFs than VSEfm.

Revisiting the personal protective equipment components of transmission-based precautions for the prevention of COVID-19 and other respiratory virus infections in healthcare.

The COVID-19 pandemic highlighted some potential limitations of transmission-based precautions. The distinction between transmission through large droplets vs aerosols, which have been fundamental concepts guiding infection control measures, has been questioned, leading to considerable variation in expert recommendations on transmission-based precautions for COVID-19. Furthermore, the application of elements of contact precautions, such as the use of gloves and gowns, is based on low-quality and inconclusive evidence and may have unintended consequences, such as increased incidence of healthcare-associated infections and spread of multidrug-resistant organisms. These observations indicate a need for high-quality studies to address the knowledge gaps and a need to revisit the theoretical background regarding various modes of transmission and the definitions of terms related to transmission. Further, we should examine the implications these definitions have on the following components of transmission-based precautions: (i) respiratory protection, (ii) use of gloves and gowns for the prevention of respiratory virus infections, (iii) aerosol-generating procedures and (iv) universal masking in healthcare settings as a control measure especially during seasonal epidemics. Such a review would ensure that transmission-based precautions are consistent and rationally based on available evidence, which would facilitate decision-making, guidance development and training, as well as their application in practice.

Intraregional hospital outbreak of OXA-244-producing Escherichia coli ST38 in Norway, 2020.

Infections with OXA-244-carbapenemase-producing Escherichia coli with sequence type (ST)38 have recently increased in Europe. Due to its low-level activity against carbapenems, OXA-244 can be difficult to detect. Previous assessments have not revealed a clear source and route of transmission for OXA-244-producing E. coli, but there are indications of non-healthcare related sources and community spread. Here we report a hospital-associated outbreak of OXA-244-producing E. coli ST38 involving three hospitals in Western Norway in 2020. The outbreak occurred over a 5-month period and included 12 cases identified through clinical (n = 6) and screening (n = 6) samples. The transmission chain was unclear; cases were identified in several wards and there was no clear overlap of patient stay. However, all patients had been admitted to the same tertiary hospital in the region, where screening revealed an outbreak in one ward (one clinical case and five screening cases). Outbreak control measures were instigated including contact tracing, isolation, and screening; no further cases were identified in 2021. This outbreak adds another dimension to the spread of OXA-244-producing E. coli ST38, illustrating this clone's ability to establish itself in the healthcare setting. Awareness of challenges concerning OXA-244-producing E. coli diagnostic is important to prevent further spread.

Nationwide, population-based observational study of the molecular epidemiology and temporal trend of carbapenemase-producing Enterobacterales in Norway, 2015 to 2021.

IntroductionNational and regional carbapenemase-producing Enterobacterales (CPE) surveillance is essential to understand the burden of antimicrobial resistance, elucidate outbreaks, and develop infection-control or antimicrobial-treatment recommendations.AimThis study aimed to describe CPE and their epidemiology in Norway from 2015 to 2021.MethodsA nationwide, population-based observational study of all verified clinical and carriage CPE isolates submitted to the national reference laboratory was conducted. Isolates were characterised by antimicrobial susceptibility testing, whole genome sequencing (WGS) and basic metadata. Annual CPE incidences were also estimated.ResultsA total of 389 CPE isolates were identified from 332 patients of 63 years median age (range: 0-98). These corresponded to 341 cases, 184 (54%) being male. Between 2015 and 2021, the annual incidence of CPE cases increased from 0.6 to 1.1 per 100,000 person-years. For CPE-isolates with available data on colonisation/infection, 58% (226/389) were associated with colonisation and 38% (149/389) with clinical infections. WGS revealed a predominance of OXA-48-like (51%; 198/389) and NDM (34%; 134/389) carbapenemases in a diversified population of Escherichia coli and Klebsiella pneumoniae, including high-risk clones also detected globally. Most CPE isolates were travel-related (63%; 245/389). Although local outbreaks and healthcare-associated transmission occurred, no interregional spread was detected. Nevertheless, 18% (70/389) of isolates not directly related to import points towards potentially unidentified transmission routes. A decline in travel-associated cases was observed during the COVID-19 pandemic.ConclusionsThe close-to-doubling of CPE case incidence between 2015 and 2021 was associated with foreign travel and genomic diversity. To limit further transmission and outbreaks, continued screening and monitoring is essential.

Clinical outcomes of antimicrobial resistance in cancer patients: a systematic review of multivariable models.

BACKGROUND: Infections are major causes of disease in cancer patients and pose a major obstacle to the success of cancer care. The global rise of antimicrobial resistance threatens to make these obstacles even greater and hinder continuing progress in cancer care. To prevent and handle such infections, better models of clinical outcomes building on current knowledge are needed. This internally funded systematic review (PROSPERO registration: CRD42021282769) aimed to review multivariable models of resistant infections/colonisations and corresponding mortality, what risk factors have been investigated, and with what methodological approaches. METHODS: We employed two broad searches of antimicrobial resistance in cancer patients, using terms associated with antimicrobial resistance, in MEDLINE and Embase through Ovid, in addition to Cinahl through EBSCOhost and Web of Science Core Collection. Primary, observational studies in English from January 2015 to November 2021 on human cancer patients that explicitly modelled infection/colonisation or mortality associated with antimicrobial resistance in a multivariable model were included. We extracted data on the study populations and their malignancies, risk factors, microbial aetiology, and methods for variable selection, and assessed the risk of bias using the NHLBI Study Quality Assessment Tools. RESULTS: Two searches yielded a total of 27,151 unique records, of which 144 studies were included after screening and reading. Of the outcomes studied, mortality was the most common (68/144, 47%). Forty-five per cent (65/144) of the studies focused on haemato-oncological patients, and 27% (39/144) studied several bacteria or fungi. Studies included a median of 200 patients and 46 events. One-hundred-and-three (72%) studies used a p-value-based variable selection. Studies included a median of seven variables in the final (and largest) model, which yielded a median of 7 events per variable. An in-depth example of vancomycin-resistant enterococci was reported. CONCLUSIONS: We found the current research to be heterogeneous in the approaches to studying this topic. Methodological choices resulting in very diverse models made it difficult or even impossible to draw statistical inferences and summarise what risk factors were of clinical relevance. The development and adherence to more standardised protocols that build on existing literature are urgent.

A new method for near real-time, nationwide surveillance of nosocomial COVID-19 in Norway: providing data at all levels of the healthcare system, March 2020 to March 2022.

BackgroundGreat efforts have been made to minimise spread and prevent outbreaks of COVID-19 in hospitals. However, there is uncertainty in identifying nosocomial vs community-acquired infections. To minimise risks and evaluate measures, timely data on infection risk in healthcare institutions are required.AimsTo design an automated nationwide surveillance system for nosocomial COVID-19 using existing data to analyse the impact of community infection rates on nosocomial infections, to explore how changes in case definitions influence incidence and to identify patients and wards at highest risk and effects of SARS-CoV-2 variants.MethodsWe used data from the Norwegian real-time emergency preparedness register (Beredt C19), which includes all patients nationwide admitted to Norwegian hospitals between March 2020 and March 2022 with a positive SARS-CoV-2 PCR test during their hospital stay or within 7 days post-discharge. COVID-19 cases were assigned to categories depending on the time between admission and testing.ResultsInfection rates for definite/probable nosocomial COVID-19 increased from 0.081% in year 1 to 0.50% in year 2 in hospital admissions 7 days or longer. Varying the definitions resulted in large changes in registered nosocomial infections. Infection rates were similar across different ward types. By 2022, 58% of patients with a definite/probable nosocomial infection had received three vaccine doses.ConclusionAutomated national surveillance for nosocomial COVID-19 is possible based on existing data sources. Beredt C19 provided detailed information with only 5% missing data on hospitals/wards. Epidemiological definitions are possible to standardise, enabling easier comparison between regions and countries.

A new automated national register-based surveillance system for outbreaks in long-term care facilities in Norway detected three times more severe acute respiratory coronavirus virus 2 (SARS-CoV-2) clusters than traditional methods.

OBJECTIVE: To develop and test a new automated surveillance system that can detect, define and characterize infection clusters, including coronavirus disease 2019 (COVID-19), in long-term care facilities (LTCFs) in Norway by combining existing national register data. BACKGROUND: The numerous outbreaks in LTCFs during the COVID-19 pandemic highlighted the need for accurate and timely outbreak surveillance. As traditional methods were inadequate, we used severe acute respiratory coronavirus virus 2 (SARS-CoV-2) as a model to test automated surveillance. METHODS: We conducted a nationwide study using data from the Norwegian preparedness register (Beredt C19) and defined the study population as an open cohort from January 2020 to December 2021. We analyzed clusters (≥3 individuals with positive SARS-CoV-2 test ≤14 days) by 4-month periods including cluster size, duration and composition, and residents' mortality associated with clusters. RESULTS: The study population included 173,907 individuals; 78% employees and 22% residents. Clusters were detected in 427 (43%) of 993 LTCFs. The median cluster size was 4-8 individuals (maximum, 50) by 4-month periods, with a median duration of 9-17 days. Employees represented 60%-82% of cases in clusters and were index cases in 60%-90%. In the last 4-month period of 2020, we detected 107 clusters (915 cases) versus 428 clusters (2,998 cases) in the last period of 2021. The 14-day all-cause mortality rate was higher in resident cases from the clusters. Varying the cluster definitions changed the number of clusters. CONCLUSION: Automated national surveillance for SARS-CoV-2 clusters in LTCFs is possible based on existing data sources and provides near real-time detailed information on size, duration, and composition of clusters. Thus, this system can assist in early outbreak detection and improve surveillance.

Transmission of severe acute respiratory coronavirus virus 2 (SARS-CoV-2) between hospital workers and members of their household: Nationwide, registry-based, cohort study from Norway.

BACKGROUND: Understanding and limiting infection in healthcare workers (HCWs) and subsequent transmission to their families is always important and has been underscored during the COVID-19 pandemic. Except in specific and local settings, little is known about the extent of such transmissions at the national level. OBJECTIVE: To describe SARS-CoV-2 infection in HCWs and to estimate the risk of HCWs transmitting COVID-19 to their household members, including calculating the secondary attack rate to household members and estimating the risk for hospital workers to contract COVID-19 at home. METHODS: Using individual-level data on all HCWs employed in Norwegian hospitals and their household members, we identified (1) the number of HCWs who tested positive for SARS-CoV-2 between August 2020 and September 2021 and the proportion of those who were index cases in their own household and (2) the number of HCWs who were secondary cases in their own households. RESULTS: During this period, ∼3,005 (2,6%) hospital workers acquired COVID-19. Almost half of all hospital workers with confirmed COVID-19 were likely index cases in their own households. When the index case in a family was an HCW, the secondary attack rate was 24.8%. At least 17.8% of all confirmed COVID-19 cases among hospital workers were acquired in the household. CONCLUSIONS: Our results suggest not only that many HCWs are infected with SARS-CoV-2 in their households but also that infected HCWs constitute a serious infection risk to members of the HCW's household.

Effect of Wearing Glasses on Risk of Infection With SARS-CoV-2 in the Community: A Randomized Clinical Trial.

Importance: Observational studies have reported an association between the use of eye protection and reduced risk of infection with SARS-CoV-2 and other respiratory viruses, but, as with most infection control measures, no randomized clinical trials have been conducted. Objectives: To evaluate the effectiveness of wearing glasses in public as protection against being infected with SARS-CoV-2 and other respiratory viruses. Design, Setting, and Participants: A randomized clinical trial was conducted in Norway from February 2 to April 24, 2022; all adult members of the public who did not regularly wear glasses, had no symptoms of COVID-19, and did not have COVID-19 in the last 6 weeks were eligible. Intervention: Wearing glasses (eg, sunglasses) when close to others in public spaces for 2 weeks. Main Outcomes and Measures: The primary outcome was a positive COVID-19 test result reported to the Norwegian Surveillance System for Communicable Diseases. Secondary outcomes included a positive COVID-19 test result and respiratory infection based on self-report. All analyses adhered to the intention-to-treat principle. Results: A total of 3717 adults (2439 women [65.6%]; mean [SD] age, 46.9 [15.1] years) were randomized. All were identified and followed up in the registries, and 3231 (86.9%) responded to the end of study questionnaire. The proportions with a reported positive COVID-19 test result in the national registry were 3.7% (68 of 1852) in the intervention group and 3.5% (65 of 1865) in the control group (absolute risk difference, 0.2%; 95% CI, -1.0% to 1.4%; relative risk, 1.10; 95% CI, 0.75-1.50). The proportions with a positive COVID-19 test result based on self-report were 9.6% (177 of 1852) in the intervention group and 11.5% (214 of 1865) in the control group (absolute risk difference, -1.9%; 95% CI, -3.9% to 0.1%; relative risk, 0.83; 95% CI, 0.69-1.00). The risk of respiratory infections based on self-reported symptoms was lower in the intervention group (30.8% [571 of 1852]) than in the control group (34.1% [636 of 1865]; absolute risk difference, -3.3%; 95% CI, -6.3% to -0.3%; relative risk, 0.90; 95% CI, 0.82-0.99). Conclusions and Relevance: In this randomized clinical trial, wearing glasses in the community was not protective regarding the primary outcome of a reported positive COVID-19 test. However, results were limited by a small sample size and other issues. Glasses may be worth considering as one component in infection control, pending further studies. Trial Registration: ClinicalTrials.gov Identifier: NCT05217797.

A step forward in antibiotic use and resistance monitoring: a quarterly surveillance system pilot in 11 European Union/European Economic Area countries, September 2017 to May 2020.

BackgroundSurveillance of antimicrobial resistance (AMR) and antimicrobial use (AMU) in Europe is currently annual.AimTo study the feasibility and scalability of a quarterly AMR/AMU surveillance system in the European Union/European Economic Area (EU/EEA).MethodsWe conducted a longitudinal study within the scope of the EU-JAMRAI project. Seventeen partners from 11 EU/EEA countries prospectively collected 41 AMU and AMR indicators quarterly from September 2017 to May 2020 for the hospital sector (HS) and primary care (PC). Descriptive statistics and coefficients of variation (CV) analysis were performed.ResultsData from 8 million hospital stays and 45 million inhabitants per quarter were collected at national (n = 4), regional (n = 6) and local (n = 7) levels. Of all partners, five were able to provide data within 3 months after each preceding quarter, and eight within 3-6 months. A high variability in AMU was found between partners. Colistin was the antibiotic that showed the highest CV in HS (1.40; p < 0.0001). Extended-spectrum beta-lactamase-producing Escherichia coli presented the highest incidence in HS (0.568 ± 0.045 cases/1,000 bed-days per quarter), whereas ciprofloxacin-resistant E. coli showed the highest incidence in PC (0.448 ± 0.027 cases/1,000 inhabitants per quarter). Barriers and needs for implementation were identified.ConclusionThis pilot study could be a first step towards the development of a quarterly surveillance system for AMU and AMR in both HS and PC in the EU/EEA. However, committed institutional support, dedicated human resources, coordination of data sources, homogeneous indicators and modern integrated IT systems are needed first to implement a sustainable quarterly surveillance system.

High vaccine effectiveness against coronavirus disease 2019 (COVID-19) and severe disease among residents and staff of long-term care facilities in Norway, November 2020-June 2021.

Coronavirus disease 2019 (COVID-19) causes high morbidity and mortality in long-term care facilities (LTCFs). COVID-19 vaccine effectiveness against infection was 81.5% and 81.4% among fully vaccinated residents and staff in LTCFs. The vaccine effectiveness against COVID-19-associated death was 93.1% among residents, and no hospitalizations occurred among fully vaccinated staff.

Register-based surveillance of COVID-19 in nursing homes. / Registerbasert overvåkning av covid-19 i sykehjem.

BACKGROUND: This study describes results from the surveillance of COVID-19 infections in nursing homes in the first year of the COVID-19 pandemic. MATERIAL AND METHOD: All data in the study are from Beredt C19, an emergency preparedness register that collects data from a wide range of sources. We used the data set 'Health and Care' in the Norwegian Registry for Primary Health Care to define a nursing home population and linked this to other sources in the emergency preparedness register to estimate incidence rates, hospitalisations and deaths related to COVID-19 among nursing home residents in 2020. A log-binomial regression model was used to analyse the risk of death related to COVID-19. RESULTS: Of the 83 114 persons who were included in the study, 35 758 (43 %) were older than 80 years. We found that 570 persons (0.69 %) tested positive for SARS-CoV-2 in 2020. A total of 19 041 residents died during the study period, whereof 248 (1.3 %) deaths were related to COVID-19. The relative risk of dying from COVID-19 rose with age and was highest for long-term nursing home residents. INTERPRETATION: Nursing home residents have a high background mortality, so despite the high lethality of SARS-CoV-2 infection and the high proportion of the COVID-19-related deaths that have occurred in nursing homes, COVID-19-related deaths accounted for a relatively minor proportion of all deaths among nursing home residents.

Pseudomonas aeruginosa countrywide outbreak in hospitals linked to pre-moistened non-sterile washcloths, Norway, October 2021 to April 2022.

In November 2021, a clonal outbreak of Pseudomonas aeruginosa of novel sequence type ST3875 was detected in three patients who died of bloodstream infections in one hospital. By 25 April 2022, the outbreak included 339 cases from 38 hospitals across Norway. Initial hospital reports indicate Pseudomonas infection as the main contributing cause in seven deaths. In March 2022, the outbreak strain was identified in non-sterile pre-moistened disposable washcloths, used to clean patients, from three lots from the same international manufacturer.

Risk factors, immune response and whole-genome sequencing of SARS-CoV-2 in a cruise ship outbreak in Norway.

OBJECTIVE: To improve understanding of SARS-CoV-2-transmission and prevention measures on cruise ships, we investigated a Norwegian cruise ship outbreak from July to August 2020 using a multidisciplinary approach after a rapid outbreak response launched by local and national health authorities. METHODS: We conducted a cross-sectional study among crew members using epidemiologic data and results from SARS-CoV-2 polymerase chain reaction (PCR) of nasopharynx-oropharynx samples, antibody analyses of blood samples, and whole-genome sequencing. RESULTS: We included 114 multinational crew members (71% participation), median age 36 years, and 69% male. The attack rate was 33%; 32 of 37 outbreak cases were seropositive 5-10 days after PCR. One PCR-negative participant was seropositive, suggesting a previous infection. Network-analysis showed clusters based on common exposures, including embarkation date, nationality, sharing a cabin with an infected cabin-mate (adjusted odds ratio [AOR] 3.27; 95% confidence interval [CI] 0.97-11.07, p = 0.057), and specific workplaces (mechanical operations: 9.17 [1.82-45.78], catering: 6.11 [1.83-20.38]). Breaches in testing, quarantine, and isolation practices before/during expeditions were reported. Whole-genome sequencing revealed lineage B.1.36, previously identified in Asia. Despite extensive sequencing, the continued transmission of B.1.36 in Norway was not detected. CONCLUSIONS: Our findings confirm the high risk of SARS-CoV-2-transmission on cruise ships related to workplace and cabin type and show that continued community transmission after the outbreak could be stopped by implementing immediate infection control measures at the final destination.

Increasing risk of breakthrough COVID-19 in outbreaks with high attack rates in European long-term care facilities, July to October 2021.

We collected data from 10 EU/EEA countries on 240 COVID-19 outbreaks occurring from July-October 2021 in long-term care facilities with high vaccination coverage. Among 17,268 residents, 3,832 (22.2%) COVID-19 cases were reported. Median attack rate was 18.9% (country range: 2.8-52.4%), 17.4% of cases were hospitalised, 10.2% died. In fully vaccinated residents, adjusted relative risk for COVID-19 increased with outbreak attack rate. Findings highlight the importance of early outbreak detection and rapid containment through effective infection prevention and control measures.

Transmission of SARS-CoV-2 into and within immigrant households: nationwide registry study from Norway.

BACKGROUND: Minority groups and immigrants have been hit disproportionally hard by COVID-19 in many developed countries, including Norway. METHODS: Using individual-level registry data of all Norwegian residents, we compared infections across all multiperson households. A household with at least one member born abroad was defined as an immigrant household. In households where at least one person tested positive for SARS-CoV-2 from 1 August 2020 to 1 May 2021, we calculated secondary attack rates (SARs) as the per cent of other household members testing positive within 14 days. Logistic regression was used to adjust for sex, age, household composition and geography. RESULTS: Among all multiperson households in Norway (n=1 422 411), at least one member had been infected in 3.7% of the 343 017 immigrant households and 1.4% in the 1 079 394 households with only Norwegian-born members. SARs were higher in immigrant (32%) than Norwegian-born households (20%). SARs differed considerably by region, and were particularly high in households from West Asia, Eastern Europe, Africa and East Asia, also after adjustment for sex and age of the secondary case, household composition and geography. CONCLUSION: SARS-CoV-2 is more frequently introduced into multiperson immigrant households than into households with only Norwegian-born members, and transmission within the household occurs more frequently in immigrant households. The results are likely related to living conditions, family composition or differences in social interaction, emphasising the need to prevent introduction of SARS-CoV-2 into these vulnerable households.

Birthing parents had a lower risk of testing positive for SARS-CoV-2 in the peripartum period in Norway, 15th of February 2020 to 15th of May 2021.

Hospital infection control measures against COVID-19 may come into conflict with patients' need for support. In Norway, some hospitals have restricted access for partners of women giving birth. We investigated the incidence rate of SARS-CoV-2 among birthing parents compared to similarly aged women and men in the general population; and the additional risk posed by allowing partners in. Birthing parents often shared infection status and had a slightly lower incidence rate than the general population in the peripartum period. They should not be considered a high-risk group for SARS-CoV-2 infections.

Secondary attack rates of COVID-19 in Norwegian families: a nation-wide register-based study.

To characterize the family index case for detected SARS-CoV-2 and describe testing and secondary attack rates in the family, we used individual-level administrative data of all families and all PCR tests for SARS-CoV-2 in Norway in 2020. All families with at least one parent and one child below the age of 20 who lived at the same address (N = 662,582), where at least one member, i.e. the index case, tested positive for SARS-CoV-2 in 2020, were included. Secondary attack rates (SAR7) were defined as the share of non-index family members with a positive PCR test within 7 days after the date when the index case tested positive. SARs were calculated separately for parent- and child-index cases, and for parent- and child-secondary cases. We identified 7548 families with an index case, comprising 26,991 individuals (12,184 parents, 14,808 children). The index was a parent in 66% of the cases. Among index children, 42% were in the age group 17-20 and only 8% in the age group 0-6. When the index was a parent, SAR7 was 24% (95% CI 24-25), whilst SAR7 was 14% (95% CI 13-15) when the index was a child. However, SAR7 was 24% (95% CI 20-28) when the index was a child aged 0-6 years and declined with increasing age of the index child. SAR7 from index parent to other parent was 35% (95% CI 33-36), and from index child to other children 12% (95% CI 11-13). SAR7 from index child aged 0-6 to parents was 27% (95% CI 22-33). The percent of non-index family members tested within 7 days after the index case, increased from about 20% in April to 80% in December, however, SAR7 stabilized at about 20% from May. We conclude that parents and older children are most often index cases for SARS-CoV-2 in families in Norway, while parents and young children more often transmit the virus within the family. This study suggests that whilst the absolute infection numbers are low for young children because of their low introduction rate, when infected, young children and parents transmit the virus to the same extent within the family.