CDC data shows norovirus is returning to pre-pandemic levels

September 22 2022

2 minutes to read

The authors and Cray did not make any relevant financial disclosures.

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CDC researchers reported Thursday that the norovirus outbreak has rebounded to pre-pandemic levels as COVID-19 mitigation measures ease across the country.

Data from NoroSTAT — a network of 12 states that reported norovirus outbreaks to the CDC — showed there were nearly three times as many outbreaks from August 2021 through July 2022 compared to the same time period in 2020-2021.


Participating countries reported 992 outbreaks of norovirus in 2021-2022 – close to 1,056 cases reported in 2019-2020 – after only 343 cases were reported during the 2020-2021 surveillance year.

Of the outbreaks in 2021-2022, 82% were due to person-to-person spread, with the majority – 59% – occurring in long-term care facilities. Among laboratory-confirmed outbreaks – overall about 17% of outbreaks per year – 43% were Sydney Dynasty GII.4that has dominated the outbreak in the United States since it emerged in the 2015-2016 surveillance year, the researchers said.

They said that non-pharmaceutical interventions implemented at the start of the COVID-19 pandemic were likely effective in preventing outbreaks of other infectious diseases, including norovirus.

This is echoing Report published last March by Alicia N M Cry, Ph.D., MPHAnd the Now an infectious disease epidemiologist at the University of Illinois College of Applied Health Sciences, and colleagues, who said the more than 80% drop in norovirus outbreaks between April and July 2020 may have been the result of interventions such as social distancing, mask-wearing and increased hand hygiene.

New Cray said MMWR Report “It makes sense and provides further support for this initial hypothesis.”

In addition to increased contact, we know that norovirus can infect people multiple times during their lives. After infection, people are protected from getting sick for a while, but over time this protection weakens and may eventually disappear,” Cray told Helio in an email.

“So, for norovirus, the fact that there have been fewer cases for a while may have made more people more susceptible to norovirus, which could make transmission more likely and future outbreaks more severe and contribute to the number of cases observed in 2021 2022 is the year of observation. “In other words, it’s not just about increased exposure as COVID mitigation measures are regressing, it’s about how that increased exposure interacts with the immunity of the population.”

According to the new report, 12 NoroSTAT states in the pre-COVID-19 years reported similar numbers for 2019-2020 and 2021-2022, ranging from 1,219 outbreaks in the 2015-2016 surveillance year to 1,471 outbreaks in the 2018-2019 surveillance year.

The researchers said the decline in norovirus outbreaks in the United States reflects the decline seen in other countries at the start of the COVID-19 pandemic. However, they noted, outbreak levels in the US began to increase rapidly in January 2022 – just as mitigation measures were eased in most parts of the country.

Norovirus transmission can be prevented by washing hands thoroughly, avoiding preparing food for at least two days after symptoms have passed, and properly cleaning contaminated areas, according to the CDC.