為什麼A型鏈球菌激增——科學家們有多擔心?
英國 13 名兒童的悲慘死亡以及秋季病例的異常上升讓研究人員保持警惕。
資料來源:海蒂·萊德福德 / 2022 年 12 月 9 日 / 自然 / 財團法人台灣紅絲帶基金會編譯
A型鏈球菌 (strep A) 引起的感染會引發喉嚨痛,並可能導致猩紅熱,或者在極少數情況下導致更嚴重的疾病和死亡。圖片來源:CNRI/Science Photo Library
隨著每年春天白晝的延長和氣溫的升高,英國的兒科醫生知道會發生什麼:A 型鏈球菌感染的增加應該會在夏季逐漸減少。 但今年在淡季爆發的細菌感染超出了預期,自 9 月以來在英格蘭導致數十人患病並導致 13 名 15 歲以下兒童死亡。
「據我所知,我們從未在每年的這個時候看到過這樣的高峰,至少幾十年來沒有」,倫敦帝國理工學院的微生物學家 Shiranee Sriskandan 說。
一種理論認為,在 COVID-19 大流行最嚴重的封鎖期間,沒有暴露於 A 型鏈球菌 (strep A) 意味著幼兒缺乏對細菌的免疫力。 但英國謝菲爾德大學的分子微生物學家克萊爾·特納 (Claire Turner) 說,現在斷言這是否是 A 型鏈球菌激增的原因還為時過早。
「在封鎖之後發生了很多看起來有點奇怪的事情」,她說。「但很難說這是否導致了現在的激增,尤其是考慮到我們在大流行之前就已經出現激增」。
猩紅熱
鏈球菌 A 感染最常表現為輕度喉嚨痛(通常稱為鏈球菌性咽喉炎)或皮膚感染。 偶爾,這會導致一種叫做猩紅熱的病症,這種病症通常會影響年幼的學童,其特徵是喉嚨痛、高燒和粗糙的皮疹。 如果及時發現,鏈球菌 A 感染通常可以用抗生素治療。
在極少數情況下,鏈球菌 A 會導致更嚴重的疾病,稱為侵襲性 A 群鏈球菌感染,尤其是在免疫系統受損的人群中。 這可能導致包括腦膜炎、中毒性休克綜合症和壞死性筋膜炎在內的病症,這是一種皮膚下組織迅速進展的感染,有時被稱為食肉病。
在英格蘭,猩紅熱受到嚴密追踪,醫生必須向衛生當局報告病例。 9 月中旬至 11 月中旬,英格蘭有 4,622 起猩紅熱報告,而過去五年同期的平均水準為 1,294 起。 (大英國協的其他國家分別追踪健康統計數據。)
Sriskandan 說,這些數字並未顯示該國 A 型鏈球菌感染的真實程度。「猩紅熱只是鏈球菌性喉炎的冰山一角」,她說。「這是社區中正在發生的事情的一個非常明顯的標誌」。
全面湧現
阿姆斯特丹大學醫學中心的微生物學家 Nina van Sorge 說,在其他國家也觀察到了類似的淡季 A 型鏈球菌感染激增模式。「這絕對不僅僅是英國的事情」,她說。「荷蘭的病例仍然非常多」。
Sriskandan 說,英格蘭多年來一直在經歷高水平的春季猩紅熱,並且在 2018 年出現了「全面的激增」。 她說,每次激增都會帶來比以前占主導地位的版本更適應菌株的擴展,而在 2016 年左右成為主要版本的菌株恰好特別容易導致嚴重疾病。
2020 年初,英國兒科醫生正準備迎接艱難的鏈球菌 A 季。 然後大流行席捲而來,學校關閉,人們呆在家裡,呼吸道感染和猩紅熱的發病率直線下降。
但 2022 年帶來了更多的社會融合——以及更多的猩紅熱。 而今年夏季的比率並沒有像預期的那樣下降。相反地,英格蘭的猩紅熱病例數繼續攀升,在學校放假期間有短暫的平靜。
封鎖是罪魁禍首嗎?
將激增歸咎於在大流行高峰期間缺乏暴露鏈球菌 A 的理論正在討論中。 這種暴露差距也被歸咎於今年流感、水痘和呼吸道融合病毒 (RSV) 發病率的增加。
特納和她的團隊希望使用實驗室培養的扁桃體細胞的 3D 培養物來評估今年激增的樣本。 他們希望更多地了解今年的菌株在感染喉嚨方面是否與以往不同。
目前,衛生官員正在努力提高公眾和醫生對淡季疫情爆發的認識。 嚴重的 A 型鏈球菌感染可能進展迅速:van Sorge 說,在荷蘭,公共衛生官員敦促醫生立即用抗生素治療疑似病例,而不是等待更多信息。
van Sorge 說,如果當前的激增與大流行病的社會疏遠有關,那麼一旦社區免疫水平得到加強,病例有望在未來幾年恢復正常的季節性模式。「我真誠地希望,在這次激增之後,孩子們會再次暴露接觸到病原,他們會增強免疫力——僅此而已」。
doi: https://doi.org/10.1038/d41586-022-04403-y
Why is strep A surging — and how worried are scientists?
The tragic deaths of 13 children in England and an unusual rise in autumn cases have put researchers on alert.
Heidi Ledford / 09 December 2022 / nature
Group A streptococcal bacteria (strep A) cause infections that trigger a sore throat — and can lead to scarlet fever or, rarely, more serious conditions and death.Credit: CNRI/Science Photo Library
As the days lengthen and temperatures rise each spring, British paediatricians know what to expect: an increase in group A streptococcal infections that should tail off by the summer. But an off-season outbreak of the bacterial infections this year has jumbled expectations, made scores of people ill and killed 13 children under the age of 15 in England since September.
“To my knowledge, we’ve never seen a peak like this at this time of year, at least not for decades,” says microbiologist Shiranee Sriskandan at Imperial College London.
One theory is that lack of exposure to group A Streptococcus (strep A) during lockdowns at the height of the COVID-19 pandemic means that young children lack immunity against the bacteria. But it is too early to say for certain if this is behind the strep A surge, says molecular microbiologist Claire Turner at the University of Sheffield, UK.
“There are a lot of things that seem to be a bit strange happening after the lockdowns,” she says. “But it’s hard to say whether that’s causing the surge right now, especially given that we have had surges prior to the pandemic.”
Scarlet fever
A strep A infection most often presents as a mild sore throat (often called strep throat) or skin infection. Occasionally, this can lead to a condition called scarlet fever, which typically affects young school children and is characterized by a sore throat, high fever and rough skin rash. If caught in time, strep A infections can usually be treated with antibiotics.
In rare instances, strep A can lead to a more serious condition called invasive group A streptococcal infection, particularly in people with compromised immune systems. This can cause conditions including meningitis, toxic shock syndrome and necrotizing fasciitis, a swiftly progressing infection of the tissue under the skin that is sometimes called flesh-eating disease.
In England, scarlet fever is carefully tracked, and physicians are required to report cases to health authorities. Between mid-September and mid-November, there were 4,622 notifications of scarlet fever in England, compared with an average of 1,294 in the same period over the past five years. (The other nations of the United Kingdom track health statistics separately.)
Those numbers don’t show the true extent of strep A infections in the country, says Sriskandan. “Scarlet fever is the tip of the strep-throat iceberg,” she says. “It’s a very visible marker of what’s going on in the community.”
Almighty surge
A similar pattern of off-season strep A infections is being observed in other countries, too, says microbiologist Nina van Sorge at the Amsterdam University Medical Center. “It’s definitely not just a UK thing,” she says. “Cases are still remarkably high in the Netherlands.”
England has been experiencing high levels of springtime scarlet fever for years, and in 2018 there was an “almighty surge”, says Sriskandan. Each surge brings an expansion of strains that are fitter than previously dominant versions, and one that became dominant around 2016 happened to be particularly prone to causing serious illness, she says.
In early 2020, UK paediatricians were bracing themselves for a rough strep A season. Then the pandemic swept in, schools closed, people stayed at home and rates of respiratory infections and scarlet fever plummeted.
But 2022 has brought more social mixing — and more scarlet fever. And this year, rates did not fall in the summer as expected. Instead, the number of cases of scarlet fever in England has continued to climb, with brief lulls when schools were closed for holidays.
Are lockdowns to blame?
The theory that the surge can be blamed on a lack of exposure to strep A during the height of the pandemic is under discussion. This gap in exposure has also been blamed for this year’s increased rates of influenza, chicken pox and respiratory syncytial virus (RSV).
Turner and her team are hoping to evaluate samples from this year’s surge using 3D cultures of tonsil cells grown in the laboratory. They hope to learn more about whether this year’s strains differ from previous ones in how they infect the throat.
For now, health officials are trying to raise awareness among the public and physicians about the off-season outbreaks. Serious strep A infections can progress quickly: in the Netherlands, public-health officials have urged physicians to treat suspected cases with antibiotics immediately, rather than wait for more information, says van Sorge.
If the current surge is related to pandemic social distancing, the hope is that cases will return to their normal seasonal patterns in the coming years, once community levels of immunity are bolstered, says van Sorge. “I would sincerely hope that after this surge, kids will have been exposed again, they will build up immunity — and that’s it.”
doi: https://doi.org/10.1038/d41586-022-04403-y