More than a million people in the US may not have regained sense of smell months after Covid-19 infection, study estimates
The Covid-19 pandemic has brought on an "emerging public health concern" of people losing their sense of smell, according to new research published Thursday.
The research published in JAMA Otolaryngology-Head & Neck Surgery estimated that between 700,000 and 1.6 million people in the US who had Covid-19 have lost or had a change in their sense of smell that has lasted for more than 6 months. This is likely an underestimate, the authors from Washington University School of Medicine in St. Louis said.
The study suggests most people recover their sense of smell eventually, but some may never regain it. The authors consider this a concern because, by comparison, prior to the pandemic, only 13.3 million adults age 40 and older had what scientists call olfactory dysfunction (OD) or chronic olfactory dysfunction (COD).
"These data suggest an emerging public health concern of OD and the urgent need for research that focuses on treating COVID-19 COD," the study said.
A study last year found that 72% of people with Covid-19 recovered their sense of smell after a month, but for some, it is a much slower process.
"The long-term disease burden from this, we're literally going to be dealing with this for decades," according to John Hayes, director of the Sensory Evaluation Center at Penn State's College of Agricultural Sciences. Hayes did not work on this study but has done research in the area.
He thinks the estimated number of people in the study with this problem is conservative and the issue could impact many millions more.
While a long-term loss of a sense of smell may sound trivial compared with other symptoms of long Covid, such as chronic fatigue or heart problems, not being able to smell can be dangerous, he said. A 2014 study found people who have lost their sense of smell were more than twice as likely to experience hazards such as eating spoiled food, as those who did have a sense of smell. A loss of a sense of smell has also been linked to depression in earlier studies.
"It's really consequential to appetite and social relations, like people have lost their sense of smell may not be able to detect if they have body odor, and can impact diet too," Hayes said.
Hayes said his research with Covid-19 patients has shown that they've experienced three different kinds of long-term olfactory disturbances.
Some lose or have a diminished sense of smell. Some have a sense of smell that is off, where instead of flowers, for example, someone would smell stinky feet. Others may have what Hayes calls a kind of "phantom limb syndrome" for a sense of smell, where people smell things that aren't actually there, like a persistent chemical or burning smell.
Dr. Sandeep Robert Datta, a neurobiologist at Harvard Medical School who has been studying why people with Covid-19 lose their sense of smell, said this is an important line of research.
"We've never really had a formal estimate made of how many people have been struggling with this," Datta said. "This is a really unusual event in terms of olfactory dysfunction and an unprecedented consequence of a pandemic that's never really been observed before."
Unless someone breaks their nose in an accident, or had some other kind of head trauma, it's unusual for younger people to lose their sense of smell, particularly from a virus. As people age, some do lose some sense of smell. One study found 60 to 70% of people 80 years and older have some degree of smell dysfunction. Other studies suggests it may impact fewer people, but this loss typically happens slowly over time; an acute loss is unusual.
Scientists are still trying to figure out why people with Covid-19 lose a sense of smell. Datta said the consensus seems to be that there is a disruption in the support cells in the nose. He said it's unlikely that the neurons responsible for detecting odors are being directly attacked by the virus.
"After that, there's still a lot of mystery as to what's going on and in many labs, including my own, we continue to work on this problem," Datta said.
Understanding how Covid-19 has warped someone's sense of smell will be important for scientists to determine how to help them regain it, if it doesn't come back on its own.
Some long Covid clinics have been offering a kind of physical therapy for the nose and retraining people's sense of smell by exposing them to certain odors so they can try and relearn them. Studies show this can work for some people, but not everyone.
"I had a patient call me the other day and ask what could be done and honestly, I don't have any good recommendations yet," Hayes said.
研究估计，在 Covid-19 感染数月后，美国有超过 100 万人可能无法恢复嗅觉
根据周四发表的新研究，Covid-19 大流行已经引发了人们失去嗅觉的“新出现的公共卫生问题”。
发表在 JAMA Otolaryngology-Head & Neck Surgery 上的研究估计，美国有 700,000 至 160 万患有 Covid-19 的人的嗅觉丧失或改变持续了 6 个月以上。圣路易斯华盛顿大学医学院的作者说，这可能被低估了。
该研究表明，大多数人最终会恢复嗅觉，但有些人可能永远不会恢复。作者认为这是一个问题，因为相比之下，在大流行之前，只有 1330 万 40 岁及以上的成年人患有科学家所说的嗅觉功能障碍 (OD) 或慢性嗅觉功能障碍 (COD)。
“这些数据表明 OD 出现了一个新的公共卫生问题，迫切需要专注于治疗 COVID-19 COD 的研究，”该研究说。
去年的一项研究发现，72% 的 Covid-19 患者在一个月后恢复了嗅觉，但对某些人来说，这是一个慢得多的过程。
宾夕法尼亚州立大学农业科学学院感官评估中心主任约翰·海耶斯 (John Hayes) 表示：“由此产生的长期疾病负担，我们实际上将在几十年内处理这个问题。”海耶斯没有从事这项研究，但在该领域进行了研究。
他认为研究中估计有这个问题的人数是保守的，这个问题可能会影响数百万人。
他说，虽然与长期 Covid 的其他症状（例如慢性疲劳或心脏问题）相比，长期失去嗅觉可能听起来微不足道，但无法闻到可能是危险的。 2014 年的一项研究发现，失去嗅觉的人经历诸如食用变质食物等危害的可能性是有嗅觉的人的两倍多。在早期的研究中，嗅觉丧失也与抑郁症有关。
“这对食欲和社会关系真的很重要，就像人们失去了嗅觉可能无法检测到他们是否有体味，并且也会影响饮食，”海耶斯说。
海耶斯说，他对 Covid-19 患者的研究表明，他们经历了三种不同的长期嗅觉障碍。
有些人失去嗅觉或嗅觉减弱。有些人的嗅觉是关闭的，例如，有人会闻到脚臭，而不是花。其他人可能有海耶斯所说的一种嗅觉“幻肢综合症”，人们闻到的东西实际上并不存在，比如持久的化学物质或燃烧的气味。
哈佛医学院的神经生物学家 Sandeep Robert Datta 博士一直在研究 Covid-19 患者为何会失去嗅觉，他说这是一个重要的研究方向。
达塔说：“我们从未真正对有多少人为此苦苦挣扎过进行过正式估计。” “就嗅觉功能障碍而言，这是一个非常不寻常的事件，也是前所未有的大流行病的前所未有的后果，以前从未真正观察到过。”
除非有人在事故中摔断了鼻子，或者有其他类型的头部外伤，否则年轻人失去嗅觉是不寻常的，尤其是因为病毒。随着年龄的增长，有些人确实会失去一些嗅觉。一项研究发现，80 岁及以上的人中有 60% 到 70% 有一定程度的嗅觉障碍。其他研究表明，它可能会影响更少的人，但这种损失通常会随着时间的推移缓慢发生；急性损失是不寻常的。
科学家们仍在试图弄清楚为什么患有 Covid-19 的人会失去嗅觉。达塔说，大家的共识似乎是鼻子中的支持细胞出现了破坏。他说负责检测气味的神经元不太可能直接受到病毒的攻击。
“在那之后，关于发生了什么仍然有很多谜团，在包括我自己在内的许多实验室中，我们继续研究这个问题，”达塔说。
了解 Covid-19 如何扭曲某人的嗅觉对于科学家确定如何帮助他们恢复嗅觉很重要，如果它不能自行恢复。
一些长期的 Covid 诊所一直在为鼻子提供一种物理疗法，并通过让人们接触某些气味来重新训练人们的嗅觉，以便他们可以尝试重新学习它们。研究表明这对某些人有效，但不是所有人。
“前几天我有一个病人打电话给我，问我可以做什么，老实说，我还没有任何好的建议，”海耶斯说。
