Human norovirus is a major cause of viral gastroenteritis in all age groups. The virus is constantly and rapidly changing, allowing mutations and recombination events to create great diversity of circulating viruses. With the start of the COVID-19 pandemic in 2020, a wide range of public health measures were introduced worldwide to control human-to-human transmission of SARS-CoV-2. In Germany, control measures such as distance rules, contact restrictions, personal protection equipment as well as intensive hand hygiene were introduced. To better understand the effect of the measures to control the COVID-19 pandemic on incidence and the molecular epidemiological dynamics of norovirus outbreaks in Germany, we analyzed national notification data between July 2017 and December 2022 and characterized norovirus sequences circulating between January 2018 and December 2022. Compared to a reference period before the pandemic, the incidence of notified norovirus gastroenteritis decreased by 89.7% to 9.6 per 100,000 during the 2020/2021 norovirus season, corresponding to an incidence rate ratio (IRR) of 0.10. Samples from 539 outbreaks were genotyped in two regions of the viral genome from pre-pandemic (January 2018 to February 2020) and samples from 208 outbreaks during pandemic time period (March 2020 to December 2022). As expected, norovirus outbreaks were mainly found in child care facilities and nursing homes. In total, 36 genotypes were detected in the study period. A high proportion of recombinant strains (86%) was found in patients, the proportion of detected recombinant viruses did not vary between the pre-pandemic and pandemic phase. The proportion of the predominant recombinant strain GII.4 Sydney[P16] was unchanged before pandemic and during pandemic at 37.5%. The diversity of most common genotypes in nursing homes and child care facilities showed a different proportion of genotypes causing outbreaks. In nursing homes as well as in child care facilities GII.4 Sydney[P16] was predominant during the whole study period. Compared to the nursing homes, a greater variety of genotypes at the expense of GII.4 Sydney[P16] was detected in child care facilities. Furthermore, the overall proportion of recombinant strain GII.3[P12] increased during the pandemic, due to outbreaks in child care facilities. The COVID-19 pandemic had a high impact on the occurrence of sporadic cases and norovirus outbreaks in Germany, leading to a near suppression of the typical norovirus winter season following the start of the pandemic. The number of norovirus-associated outbreak samples sent to the Consultant Laboratory dropped by 63% during the pandemic. We could not identify a clear influence on circulating norovirus genotypes. The dominance of GII.4 Sydney recombinant strains was independent from the pandemic. Further studies are needed to follow up on the diversity of less predominant genotypes to see if the pandemic could have acted as a bottleneck to the spread of previously minoritized genotypes like GII.3[P12].

中文翻译：

---

COVID-19 大流行对德国诺如病毒传播的影响

人类诺如病毒是所有年龄段病毒性胃肠炎的主要原因。病毒不断快速变化，突变和重组事件创造了传播病毒的多样性。随着 2020 年 COVID-19 大流行的开始，世界范围内采取了广泛的公共卫生措施来控制 SARS-CoV-2 的人际传播。德国引入了距离规则、接触限制、个人防护设备以及强化手部卫生等控制措施。为了更好地了解控制 COVID-19 大流行的措施对德国诺如病毒爆发的发病率和分子流行病学动态的影响，我们分析了 2017 年 7 月至 2022 年 12 月期间的国家通报数据，并对 2018 年 1 月至 2022 年 12 月期间传播的诺如病毒序列进行了特征分析与大流行前的参考期相比，2020/2021诺如病毒季节期间，通报的诺如病毒胃肠炎发病率下降了89.7%，降至每10万人中9.6例，对应的发病率比（IRR）为0.10。对大流行前（2018 年 1 月至 2020 年 2 月）的 539 起疫情爆发的样本和大流行期间（2020 年 3 月至 2022 年 12 月）的 208 起疫情的样本进行了病毒基因组的两个区域的基因分型。正如预期，诺如病毒疫情主要出现在托儿所和疗养院。研究期间总共检测到 36 种基因型。在患者中发现了高比例的重组病毒株（86％），检测到的重组病毒的比例在大流行前和大流行阶段之间没有变化。优势重组株GII.4 Sydney[P16]的比例在大流行前和大流行期间没有变化，为37.5%。疗养院和儿童保育设施中最常见基因型的多样性表明，导致疫情暴发的基因型比例不同。在疗养院和儿童保育机构中，GII.4 悉尼[P16] 在整个研究期间占主导地位。与疗养院相比，在托儿所中检测到了更多的基因型，但 GII.4 Sydney[P16] 被检测到。此外，由于儿童保育设施中的疫情爆发，重组菌株 GII.3[P12] 的总体比例在大流行期间有所增加。 COVID-19大流行对德国散发病例和诺如病毒爆发产生了很大影响，导致大流行开始后典型的诺如病毒冬季几乎受到抑制。疫情期间，送往顾问实验室的诺如病毒相关疫情样本数量下降了 63%。我们无法确定对流行的诺如病毒基因型的明显影响。 GII.4 Sydney 重组菌株的优势与大流行无关。需要进一步研究来追踪不太占主导地位的基因型的多样性，看看这种流行病是否可能成为先前少数基因型（如 GII.3[P12]）传播的瓶颈。