Department of Clinical Microbiology, Karolinska University Hospital, Stockholm, Sweden.
Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden.
Euro Surveill. 2024 Oct;29(41). doi: 10.2807/1560-7917.ES.2024.29.41.2400021.
BackgroundDespite the unprecedented measures implemented globally in early 2020 to prevent the spread of SARS-CoV-2, Sweden, as many other countries, experienced a severe first wave during the COVID-19 pandemic.AimWe investigated the introduction and spread of SARS-CoV-2 into Sweden.MethodsWe analysed stored respiratory specimens (n = 1,979), sampled 7 February-2 April 2020, by PCR for SARS-CoV-2 and sequenced PCR-positive specimens. Sequences generated from newly detected cases and stored positive specimens February-June 2020 (n = 954) were combined with sequences (Sweden: n = 730; other countries: n = 129,913) retrieved from other sources for Nextstrain clade assignment and phylogenetic analyses.ResultsTwelve previously unrecognised SARS-CoV-2 cases were identified: the earliest was sampled on 3 March, 1 week before recognised community transmission. We showed an early influx of clades 20A and 20B from Italy (201/328, 61% of cases exposed abroad) and clades 19A and 20C from Austria (61/328, 19%). Clade 20C dominated the first wave (20C: 908/1,684, 54%; 20B: 438/1,684, 26%; 20A: 263/1,684, 16%), and 800 of 1,684 (48%) Swedish sequences formed a country-specific 20C cluster defined by a spike mutation (G24368T). At the regional level, the proportion of clade 20C sequences correlated with an earlier weighted mean date of COVID-19 deaths.ConclusionCommunity transmission in Sweden started when mitigation efforts still focused on preventing influx. This created a transmission advantage for clade 20C, likely introduced from ongoing cryptic spread in Austria. Therefore, pandemic preparedness should have a comprehensive approach, including capacity for large-scale diagnostics to allow early detection of travel-related cases and community transmission.
背景
尽管 2020 年初全球采取了前所未有的措施来阻止 SARS-CoV-2 的传播，但瑞典与许多其他国家一样，在 COVID-19 大流行期间经历了严重的第一波疫情。
目的
我们研究了 SARS-CoV-2 进入瑞典的情况。
方法
我们通过 PCR 分析了 2020 年 2 月 7 日至 4 月 2 日采集的 1979 份储存的呼吸道标本，对 SARS-CoV-2 进行了检测，并对 PCR 阳性标本进行了测序。从 2020 年 2 月至 6 月新发现的病例和储存的阳性标本中生成的序列（瑞典：n=954；其他国家：n=129913）与其他来源检索到的序列（瑞典：n=730；其他国家：n=129913）一起进行 Nextstrain 分支分配和系统发育分析。
结果
确定了 12 例先前未识别的 SARS-CoV-2 病例：最早的病例于 3 月 3 日采样，比公认的社区传播早了 1 周。我们发现来自意大利的 20A 和 20B 分支（201/328，暴露于国外的病例的 61%）和来自奥地利的 19A 和 20C 分支（61/328，19%）大量涌入。20C 分支主导了第一波疫情（20C：908/1684，54%；20B：438/1684，26%；20A：263/1684，16%），在 1684 例瑞典序列中，有 800 例形成了一个由刺突突变（G24368T）定义的特定国家的 20C 聚类。在区域层面上，20C 序列的比例与 COVID-19 死亡的加权平均日期更早相关。
结论
当缓解措施仍集中在防止传入时，瑞典的社区传播就开始了。这为 20C 分支创造了传播优势，该分支可能是由奥地利持续的隐匿传播引入的。因此，大流行防范应该采取综合方法，包括进行大规模诊断的能力，以便及早发现与旅行相关的病例和社区传播。
