According to an analysis of pathogens during the coronavirus pandemic, Listeria and E. coli infections returned to expected levels quicker than Salmonella cases.

Researchers looked at the impact of the COVID-19 outbreak response on gastrointestinal infection trends using surveillance data from six national UK Health Security Agency (UKHSA) coordinated systems.

Following decreases during the first lockdown in March to May 2020, bacterial and parasitic pathogens related to foodborne or environmental transmission routes recovered rapidly between June and September 2020, while those associated with travel or person-to-person transmission remained lower than expected for 2021. High out-of-season norovirus activity was observed with the easing of lockdown measures between June and October 2021.

Viral pathogens are more likely to be transmitted from person to person, while bacterial pathogens are more commonly transmitted via foodborne routes. Viruses are frequently associated with closed settings such as schools, hospitals, or food premises, while bacterial pathogens are often acquired from food products consumed at home. 

Pathogen variety
Measures to reduce coronavirus transmission included improved hand hygiene, reduced social contact, increased environmental cleaning, and the closure of premises.

The findings follow a previous study that found reduced gastrointestinal infections during the initial six months of the COVID-19 outbreak response in England. Hypotheses to explain the decline included changes in health-seeking behavior, limited testing, changes in healthcare provision, and true decreases in incidence.

In the latest study, published in the journal Epidemiology and Infection, for lab and outbreak datasets, the pandemic period was defined as Dec. 30, 2019, to April 30, 2022, with historical data covering Dec. 29, 2014, to Dec. 29, 2019. For syndromic surveillance indicators, the historical period covered Dec. 31, 2018, to Dec. 29, 2019. Data were split into COVID-19 pandemic phases for comparison, determined by the stringency of control measures. 

Listeria and Shiga toxin-producing E. coli (STEC) activity returned to expected levels from May 2020 with the easing of lockdown measures, while Campylobacter returned to normal in November 2020. Reports remained comparable to or higher than historical figures for the rest of the pandemic.

Reports of lab-confirmed Cryptosporidium, Giardia, Shigella, and Salmonella remained substantially lower than historical figures across the pandemic period. Levels for all bacterial and parasitic pathogens, except for Giardia, returned to within or above expected figures in early 2022. 

Multiple factors behind levels
National Health Service (NHS) 111 calls for diarrhea and vomiting decreased before the first lockdown, went to a low number across the pandemic period, and increased with the easing of measures in mid-2021. Searches for the terms “Sickness bug,” “Gastroenteritis,” and “Food poisoning” showed low activity across the pandemic period until the easing of restrictions in mid-2021, according to syndromic surveillance and Google Trends data.

Across the pandemic period, the activity of enteric pathogens correlated with stages in the response. Periods of higher pathogen activity corresponded to the relaxation of initial measures, and lower levels matched the reimplementation of further control measures with subsequent COVID-19 waves.

It is possible that people with more severe and prolonged infections, such as STEC, were more likely to access care or that bloody diarrhea specimens were prioritized for testing. Scientists said Salmonella remained lower than historical figures for 2020/2021, likely impacted by travel restrictions.

Many control measures during COVID-19 were similar to those implemented in response to a gastrointestinal infection outbreak. The closure of food premises and restrictions on mass gatherings and catered events probably reduced the risks associated with foodborne illness. Two peaks were observed in summer 2020, corresponding to restaurants reopening to dine-in customers and England’s “Eat Out to Help Out” initiative.

“We show that following the end of the first lockdown in 2020, the activity of foodborne pathogens such as STEC and Campylobacter quickly returned to historic levels, while pathogens more associated with person-to-person transmission or foreign travel, and therefore more influenced by hand hygiene, social distancing measures, and travel regulations, recovered at a slower rate,” said researchers.

“These findings suggest that although rapid changes to healthcare provision altered health-seeking behavior and non-COVID-19 testing capacity likely resulted in initial decreases observed across surveillance systems, there were true pathogen-specific reductions in incidence due to implemented measures.”