Referrals for diagnosis of selected notifiable diseases during Covid-19 epidemic
By comparing selected test-based indicators for the period March-September 2020, with the "normal" laboratory function before the covid-19 epidemic, we will in this project assess how the covid-19 epidemic may have affected the capacity of Norwegian medical microbiological laboratories.
- Based on information from 11 diagnostic laboratories, referrals for testing of selected notifiable diseases decreased in March 2020 with the lowest testing in April 2020 compared to the period before the COVID-19 epidemic. Reduction was lowest for gonorrhoea and highest for food-and waterborne infections (campylobacteriosis, cryptosporidiosis and salmonellosis).
- The proportion of tested positive remained stable during COVID-19 epidemic for Clostrioides difficile and Borrelia while it decreased for Neisseria gonorrhoeae, Salmonella spp. and Bordetella pertussis. These trends are in line with laboratory-confirmed cases reported to MSIS and can reflect a different impact of covid-19 control measures on the epidemiology of different diseases.
- Despite reduction in testing referrals, the proportion tested positive increased for Campylobacter, Cryptosporidium spp., Staphylococcus aureus (MRSA) and Rotavirus. This scenario does not align with national trends of laboratory-confirmed cases reported to MSIS and may therefore signal affected health-seeking behaviours, availability of healthcare and/or limited laboratory resources, which could lead to referral for testing of suspect cases with more pronounced, serious symptoms. This would lead to reduced sensitivity of surveillance of some diseases.
- The reduction in testing referrals for selected pathogens was most pronounced among people under the age of 20 years and less affected with increasing age. Testing referrals for most pathogens have increased during the COVID-19 epidemic among people 60 years and older.
- The decrease in testing referrals from primary and secondary health care providers could be due to a decrease in disease risk due to effective control measures implemented for COVID-19 or due to a change in health seeking behaviours or changes in laboratory procedures due to COVID-19 response.
In March 2020, a large Covid-19 epidemic developed in Norway and strict control measures to limit the spread of infection were implemented. Measures, including social distancing, improved hand hygiene, business closures and restrictions on travel abroad, were maintained to varying degrees between March and September 2020. The long-lasting covid-19 epidemic and response activities could lead to reduced attention given to other public health issues, including surveillance of other infectious diseases. Since April 2020, the Norwegian Institute of Public Health (FHI) has published periodic reports to monitor the effect of the covid-19 epidemic on the Norwegian Surveillance System for Communicable Diseases (MSIS) function (www.fhi.no/publ/2020/covid-19-msis/). These reports have shown a significant 50-60% reduction in reports of other communicable diseases to MSIS between March and September 2020, compared to the corresponding period of 2019.
The purpose of our project was to compare the number of referrals for diagnostic testing of selected notifiable pathogens and the proportion tested positive during the covid-19 epidemic (March-September 2020) with a normal laboratory function before covid-19 started (October 2019-February 2020).
To investigate the observed reduction of notifiable disease reporting, FHI requested 22 medical microbiological laboratories in Norway to send information on referrals for diagnostic testing of 11 pathogens that represent the most frequently diagnosed infectious diseases in Norway. The request included data on the number of referrals and the number tested positive from the primary and specialist healthcare by pathogen, month of sample collection and age group. The received data were added up, cleaned and analyzed to compare testing referrals during the covid-19 epidemic (March-September 2020) with the reference period (October 2019-February 2020). In this report, we included data on 9 pathogens for which data were sufficiently complete to analyze monthly trends.
Of the 22 contacted laboratories, 11 submitted data. Completeness of the data varied by laboratory and pathogen. 11/11 laboratories provided information on the number of referrals by referral source, 10/11 submitted the number of positive tests, 8/11 submitted information on month of sampling and 8/11 submitted age groups. Completeness of variables differed by pathogen.
The number of referrals for testing of all pathogens was reduced from the primary and secondary health care in March and April 2020 compared with the preceding period. The lowest number of referrals was registered in April. The number of referrals from primary health care (GP offices and outpatient clinics) was reduced after March 2020 for all pathogens, least for Borrelia spp. (-16%) and most for Cryptosporidium spp. (-44%), Salmonella spp. (-41%) and Campylobacter spp. (40%). The highest reduction in hospital referrals was seen for Campylobacter spp. (-44%) and Salmonella spp. (-46%).
Monthly trends show a stable number of testing referrals during the covid-19 epidemic for the diagnosis of Borrelia spp. and Neisseria gonorrhoeae. Testing trends for four pathogens (Campylobacter spp., Cryptosporidium spp., Staphylococcus aureus (MRSA) and Rotavirus) show conflicting trends with a sharp reduction in the number of testing referrals during the covid-19 epidemic and at the same time an increasing proportion tested positive. For the diagnosis of Bordetella pertussis, Clostridioides difficile and Salmonella spp. a declining trend in the number of testing referrals and the proportion tested positive can be seen.
The number of testing referrals was most reduced in the age group under 20 years and less affected with increasing age. An opposite trend was seen only for referrals for the diagnosis of Cryptosporidium spp. and Neisseria gonorrhoeae in the primary healthcare. Referrals for testing of Bordetella pertussis, Borrelia spp. and Staphylococcus aureus (MRSA) in specialist healthcare appear to be equally affected in all age groups.
Reference laboratory activity followed the trends of diagnostic laboratories referrals for Salmonella spp. and Neisseria gonorrhoeae with a decrease in submissions in March-April 2020. Campylobacter spp. submissions increased during June-September 2020.
Low response (11/22) does not give a complete picture of the Norwegian diagnostic laboratories. However, these data provide an important context for the reduced MSIS reporting during the covid-19 epidemic. The number of testing referrals was most reduced in the early phase of the covid-19 response (in March-April), which was possibly related to competing needs for laboratory reagents, personnel and reporting requirements during the crisis. Stable testing maintained during the covid-19 epidemic allows interpretation of Lyme borreliosis and gonorrhea risk based on confirmed cases notified to MSIS. Also, the observation of declining trends in both test referrals and the proportion of tested positive could indicate a reduced risk of pertussis, C. difficile and salmonellosis infections due to effective control measures that led to a reduced number of suspected cases who consulted physicians and were referred for testing. However, the most problematic scenario is when testing referrals are sharply reduced and the proportion of tested positive is increasing. This may indicate reduced surveillance sensitivity which may affect the interpretation of disease risk or the identification of an outbreak.
The COVID-19 epidemic has affected laboratory function for infectious disease surveillance. After a large reduction in testing referrals for selected infectious diseases in March-April 2020, the referrals were partly restored, which may indicate that at least some of the problems were resolved. However, our investigation has documented some discrepancies, including changes in laboratory procedures reported by laboratories, as well as abnormal trends for selected pathogens and age groups, which cannot be explained with certainty by changes in infection risk. Our data has several limitations and cannot fully explain the reason for the reduction in MSIS reporting. However, we recommend the routine use of test-based indicators to place MSIS reporting in the context of test activity, based on the new quality assured MSIS laboratory database.