Researchers looking at the impact of the COVID-19 pandemic have revealed major differences between how countries monitor infections.
The study emphasized the substantial differences in transmission routes, surveillance, notification and detection methods, as well as testing and sampling practices of selected diseases across six countries.
Despite these variations, recorded case numbers for most of the five infections studied decreased during the pandemic from March 2020 to December 2021, except for listeriosis, suggesting that health-seeking behavior and healthcare access played a role in the decline of diseases with milder symptoms.
Decline in travel-related and domestic infections
Scientists described the impact of the pandemic using the number of confirmed domestically acquired and travel-related cases of campylobacteriosis, salmonellosis, hepatitis A, shigellosis, and listeriosis notified to the European Centre for Disease Prevention and Control (ECDC) between 2016 and 2021 by the Czech Republic, Denmark, Greece, the Netherlands, Norway and Sweden.
They compared the monthly median number of cases from a pre-pandemic period of January 2016 to February 2020 to those during the pandemic. Findings were published in the European Journal of Public Health.
The proportion of travel-associated cases decreased for most diseases in all countries, particularly for campylobacteriosis and salmonellosis, likely due to travel restrictions. Declines were also observed in domestically acquired cases.
In Norway, the proportion of travel-associated campylobacteriosis and salmonellosis decreased from 47 percent in 2016 to 2019 to 11 percent in 2020, and from 63 percent to 40 percent, respectively.
Pathogen and country-specific data
Campylobacteriosis caused the most infections, followed by salmonellosis, and shigellosis. Czech Republic had the highest number of cases for campylobacteriosis and salmonellosis. This was followed by Sweden. The pandemic likely influenced reporting rates because of reduced travel and fewer restaurant visits.
The lowest number of cases were reported for listeriosis, for which Sweden and the Netherlands accounted for the majority of infections.
In most countries, the notification rates for campylobacteriosis, salmonellosis, hepatitis A, and shigellosis decreased in 2020 compared to the previous years.
Listeriosis showed no common trend over the study period, likely because of the severity of the disease and the need for patients to receive medical care. Also, infections were mainly domestically acquired via food that is mostly eaten at home and so less affected by travel and hospitality restrictions.
In Denmark, the notification rate of hepatitis A was higher in 2020 compared to the year before because of an outbreak where the source was not identified. Also, listeriosis notification rates in Greece and Norway were higher in 2020 than in 2019.
There was an increase in the proportion of hospitalizations for campylobacteriosis, salmonellosis, and shigellosis in a few countries.
“Despite differences in epidemiology, healthcare and surveillance systems, immunity levels, and differences in stringency of COVID-19 measures within the countries, the notification rates of typically common food and waterborne diseases were reduced in most countries. Reasons for these declines are likely multifactorial and difficult to disentangle,” said researchers.
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