Norwegian researchers have found a decline in other notifiable infectious diseases during the Coronavirus pandemic.

They compared the number of cases reported to the Norwegian Surveillance System for Communicable Diseases (MSIS) during February to April 2020 with the median of cases in corresponding weeks during three previous years.

An observed decline in infections other than COVID-19 may indicate a reduced risk of communicable diseases because of advice and social distancing. However, it is also possible the surveillance system was affected by increased resource use due to COVID-19, according to the study published in the Journal of the Norwegian Medical Association.

“We cannot disentangle to what extent the reduction of reporting of particular notifiable diseases is the result of competing priorities and increased pressure on public health personnel and laboratories, or a real reduction in the spread and prevalence of communicable diseases. The number of negative specimens could give us some answers, but unfortunately, we do not have access to this data at national level,” said researchers.

Impact of COVID-19 on other diseases
MSIS is based on the reporting of 72 mandatory notifiable diseases by clinical microbiological laboratories and diagnosing physicians including campylobacteriosis, cryptosporidiosis, E. coli gastroenteritis, hepatitis A, listeriosis, salmonellosis, shigellosis, and Yersiniosis.

The study’s aim was to investigate a potential time association between measures against COVID-19 from February to April 2020 and incidence of other infectious diseases reported to MSIS. During the intensified COVID-19 response and increase in cases, there was a reduction in notifications of other infectious diseases to MSIS.

Compared to the median of cases during corresponding weeks in three previous years, physicians and labs reported 47 percent fewer cases (159 versus 301) in week 12; 50 percent fewer (131 vs. 261) in week 13; and 69 percent fewer (77 vs. 252) in week 14.

During February to April in 2020, there were 2,250 cases of infectious diseases registered, with 764 being foodborne and waterborne, which corresponded with previous years: 2,632 in 2019; 2,250 in 2018; and 2,283 in 2017. In weeks 6 to 11, there were more cases reported in 2020 than during corresponding weeks in 2017 to 2019.

Possible explanations for declines
Although total cases in the period was similar to previous years, researchers saw a noticeable difference in the number reported before and after mid-March. For week 14 in early April, food and waterborne diseases fell 71 percent to 24, down from 83.

Closure of restaurants and increased hand hygiene advice could have reduced the risk of food contamination, in catering services and home cooking, which may have resulted in lower risk of foodborne infections, according to the report. Travel restrictions, with fewer travelers and decreased trade in live animals and food, reduced the likelihood of infectious disease spread across borders.

Researchers said it is likely that most people working in communicable disease surveillance, locally and nationally, had to re-prioritize ongoing activities during February to April to deal with the COVID-19 pandemic. Clinical microbiological labs were under great pressure on human resources and materials use and social distancing and fear of infection may have led many to avoid seeking health care, especially if symptoms were perceived as mild.